aiorttell Ittiueraitg ffitbrarg 
 
 atJfata, Nem fork 
 
Corneir University Library 
 TL 556.L94 
 
 The book of the sky; a resume of person 
 3 1924 004 636 373 
 
Cornell University 
 Library 
 
 The original of tiiis book is in 
 tine Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924004636373 
 
THE BOOK OF THE SKY 
 
SPORTING AMONG THE FRACTO-CUMULI 
 UNDER A CEILING OF CIRRI 
 
THE BOOK OF THE SKY 
 
 A Resume of Personal 
 Experience and Observation 
 
 BY 
 
 M. LUCKIESH 
 
 Direetor of Applied Science, Nela Research Laboratories, 
 National Lamp Works of General EUctrtc Company 
 
 Author op "Colob and Its Application," "Ahtificial Light, 
 
 Its Influence upon Civilization," "Visual Illusions," 
 
 "Ultbaviolet Radiation," etc. 
 
 NEW YOEK 
 
 E. P. BUTTON & COMPANY 
 
 681 Fifth Avenue 
 
COFYEIGHT 1922, BY 
 
 E. P. DUTTON Se COMPANY 
 
 All rights reserved 
 
 A ^iL<\%-](, 
 
 Printed in the ZTntted State$ of A-meriea 
 
DEDICATED 
 TO THE MEMORY OF 
 
 PROFESSOR S. P. LANGLEY 
 
 AND OTHERS WHO LED THE WAT TOWARD 
 
 THE MASTERY OP THE AIR, 
 
 IN APPRECIATION OF THIS WONDERFUL HERITAGE. 
 
FOREWORD 
 
 nriHIS little volume grew out of experiences in flying 
 ■L wTiich have greatly augmented the author's in- 
 terest in the aerial world. The beauties, wonders, awe- 
 some spectacles, inspiring panoramas, and extensive 
 ranges of vision which await the aerial traveler, make 
 of cloudland a veritable fairyland if he will open his 
 consciousness to them. Aircraft have brought this new 
 world of experiences within easy reach of mankind and 
 it is one of the aims of this volume to awaken those who 
 fly, or would fly, to the variety of interest which air- 
 travel affords. 
 
 Furthermore, the sky holds much of interest for the 
 earthly observer who will overcome his indifference to 
 this aspect of Nature. Cloudland is full of variety. It 
 is a wonderland of clouds, weather, winds, sunsets, 
 dawns, twilights, and other interesting phenomena. It 
 will brighten many dull moments and may be depended 
 upon at all times to arouse the imagination and to sup- 
 ply something for the lover of beauty. Those who would 
 he interested technically will find an abundance of in- 
 terest in the phenomena of the atmospheric ocean above. 
 Therefore, broadly, the aim of this volume is to aid the 
 general reader in becoming more interested in cloud- 
 land. 
 
 In aiming to present the discussions in a readable 
 manner, tedious technical data have been reduced to a 
 minimum. Such material has been grouped largely in 
 a few chapters although technical facts have been in- 
 terspersed throughout the chapters with the hope that 
 they would he more palatable to the general reader in 
 this manner of presentation. Clouds are conspicuous 
 
viii FOREWORD 
 
 in some of the chapters because they are of great im- 
 portance in revealing the winds and in foretelling the 
 weather; besides they provide much of the variety and 
 beauty of the sky. The author is unaware of any modern 
 volume which discusses clouds for the general reader. 
 For this reason several chapters have been devoted to 
 clouds in order that the earthly observer and the aerial 
 traveler may learn to know them intimately and may 
 become familiar with their meanings. They become such 
 a dominating part of the sky that as one becomes fully 
 appreciative of this aspect he finds a cloudless day rather 
 uninteresting and if he is an aerial traveler he yearns 
 for that fairyland which clouds make of the aerial world. 
 
 Since the advent of flying with its modern safety, 
 convenience, and extensive possibilities, the aerial world 
 becomes more important and interesting to mankind. 
 It is believed that this little volume, which touches upon 
 so many aspects of the sky and upon what may be seen 
 and felt in cloudland, will interest the general reader 
 whether he is one who flies in reality or would fly on 
 the wings of his imagination or would be content merely 
 to admire the sky and to learn its meanings. 
 
 By intermingling the two viewpoints, namely, that of 
 the earthly observer and that of the aerial traveler, it 
 is believed the wonders of cloudland become more easily 
 visualized, recognized, and understood. By combining 
 with this plan a popular treatment throughout, it is 
 hoped that this little volume will be entertaining and 
 instructive to the general reader as well as to those who 
 have a more specific interest in the sky and in the aerial 
 world. 
 
CONTENTS 
 
 PAGE 
 
 Foreword vii 
 
 CHAPTER 
 
 I. Man Unshackled 1 
 
 n. The Countenance op Nature 12 
 
 III. The Formation of Clouds 25 
 
 IV. The Thunderbtorm 35 
 
 V. Cloud-forms 46 
 
 VI. Beyond an Overcast Sky 59 
 
 VII. Cloud-levels 67 
 
 VIII. MmoLED Moods 76 
 
 IX. Sunset Colors 85 
 
 X. Afterglow 95 
 
 XI. A PoLAB Climb 103 
 
 XII. Cloud Capers 117 
 
 XIII. A Night Flight 131 
 
 XIV. Annihilating Distance 140 
 
 XV. A Philosophy for Flying 152 
 
 XVI. Aerial Antics 162 
 
 XVII. The Supremacy op Aih-tbavel 174 
 
 XVni. Meteorology 185 
 
 XIX. Winds 197 
 
 XX. Weather and the Sky 212 
 
 XXI. The Convot 227 
 
ILLUSTRATIONS 
 
 Spoktinq among thb Pbacto-cttmuli under a Ceiling of 
 Cirri Frontispiece 
 
 Facing Page 
 In the Faibti<and op Clouds 2 
 
 Fate-weather Cumulus Clouds 12 
 
 A Majestic Sculpture of Cloudland — A Cumulo-nimbus 
 Several Miles in Height 26 
 
 One op the Awesome Spectacles op the Aerial World — 
 A Thunderstorm Viewed from the Heights 34 
 
 Billow Clouds Revealing the Huge Waves in the Aerial 
 Ocean 46 
 
 Above a Thick Blanket op Rain-cloud 60 
 
 Wind-driven Cirri above; Rolling Cumuli below 68 
 
 In the Turbulence op the Chests op Huge Cumuli 
 Clouds 76 
 
 A Huge Portion op a State Projecting into the Sea. . . 104 
 
 A Battle of Winds and Clouds 118 
 
 A Rugged Range of Thunderheads 132 
 
 A Panorama op Earth and Sky 140 
 
 The Airplane's Course and Speed are Independent op 
 Swamp, Wood, or Prairie 174 
 
 Streams and Rivers and Seas are Clouds Awaiting Resur- 
 rection. This Endless Devious Cycle Typifies the 
 Meteorological Cycle , 186 
 
 A Frowning Squall-cloud , 204 
 
 xi 
 
THE BOOK OF THE SKY 
 
THE BOOK OF THE SKY 
 
 CHAPTER I 
 
 MAN UNSHACKLED 
 
 "Here the free spirit of mankind, at length 
 Throws its last fetters off; and who shall place 
 A limit to the giant's unchained strength, 
 Or curb his swiftness in the forward race?" 
 
 — Bryant. 
 
 ON all sides Nature presents to searching eyes a 
 continuous warfare in which, no quarter is 
 asked and none is granted. The lowliest plants and 
 animals battle against tremendous odds for their 
 existence and the survivors among wild life are as 
 a whole those best fitted to struggle against their 
 hostile environment. A glimpse of this fundamen- 
 tal aspect of Nature which appears to result, at 
 least when narrowly viewed, in an extreme waste- 
 fulness and a high mortality among the forms of 
 life wholly at the mercy of Nature's whims, allevi- 
 ates in some slight degree the horror of warfare 
 among men who have broken to some slight extent 
 the shackles of utter subserviency to Nature. 
 
2 THE BOOK OF THE SKY 
 
 Man's early history is but a repetition of tlie his- 
 tory of the jungle. He fought his kind as other 
 animals in order to survive, but he early began to 
 triumph little by little over Nature. In order to 
 exist he had merely to be victor in those encoun- 
 ters which were forced upon him. In order to pro- 
 gress he had to become the aggressor and to carry 
 his warfare into many realms which for bare ex- 
 istence could be shunned. 
 
 Material progress may be measured in terms of 
 man's independence of or triumph over Nature. 
 Let the imagination drift back through the vista 
 of centuries into the remote periods of unrecorded 
 history and note the myriads of minor and major 
 victories of mankind which have led gradually 
 toward emanicipation from the bondage of Nature. 
 Natural laws still exist but mankind has learned 
 many of their secrets with the result that he 
 utilizes them against each other to his advantage. 
 In other words, intellect has harnessed many of 
 these laws so that they do man's bidding. 
 
 A fundamental of the growth of inanMnd is 
 progress. It is apparently an obsession but likely 
 it is a fundamental of the scheme of Nature. Daily, 
 hourly, and even momentarily, along the battle- 
 area of progress which covers our earth, scouting 
 parties are out and minor skirmishes are taking 
 place. These pave the way for occasional tri- 
 umphs of tremendous import. The scales are al- 
 ways tilting more and more in man's favor, but 
 these triumphs are not gained without sacrifice. 
 
MAN UNSHACKLED 3 
 
 Countless lives are dedicated to progress; some 
 through momentary risks and many through a 
 lifetime of slavery and often of suffering, ignored 
 or even persecuted by the multitude, but impelled 
 and sustained by that creative spirit which de- 
 mands discoveries from the scientist and applica- 
 tions of these from the inventive genius. 
 
 With ever-increasing momentum science has 
 added triumph after triumph until the present 
 generation complacently accepts epoch-making de- 
 velopments. Many of these developments touch 
 the multitude only indirectly though the multitude 
 is benefited by them. The masses are not suf- 
 ficiently imaginative to be thoroughly inspired by 
 scientific achievements unless they are directly in 
 touch with them. To hear and to recognize the 
 voice of a friend a thousand miles away by the 
 electrical impulses transmitted by telephone wires 
 is perhaps much more thrilling to the average per- 
 son than to receive a wireless message transcribed 
 by a third person. Both are triumphs over Nature 
 but to the masses the former is more vivid. To 
 the scientist the latter is the greater achievement. 
 Scientific protection from deadly microscopic or- 
 ganisms does not impress the average individual 
 as much as an iron grating which confines the 
 hungry lions in the cage before him. But in the 
 last analysis, triumph over Nature moves the mul- 
 titude if the victory is such as to be vividly recog- 
 nized. If it were necessary, numberless achieve- 
 ments could be cited, but consider only the com- 
 
4 THE BOOK OF THE SKY 
 
 monplace act of riding in an antomobile. A family 
 group will ride with much pleasure for hours over 
 highways which present no unusual scenery and 
 at a speed at which fruitful observation is fairly 
 difficult or even impossible. Of course, sunshine 
 and fresh air are enjoyed, but these may be ob- 
 tained to better advantage usually by walking. 
 Sitting comfortably in the automobile, gliding 
 over the highways, a great portion of the enjoy- 
 ment experienced by the average person arises 
 subconsciously from the satisfaction of not walk- 
 ing, or, in other words, of a triumph over Nature. 
 As we invoice the past we note many victories, 
 great and small, but none which has touched man- 
 kind in general more deeply than will the one 
 which now looms before us and is even enveloping 
 us. As early as the eighteenth century flight by 
 balloon had contributed many thrilling episodes 
 and in earlier centuries the evolution of balloon 
 flight is interwoven with the names of many 
 philosophers. Late in the nineteenth century some 
 progress had been made toward the use of motive 
 power which would emancipate the balloon from 
 the tyranny of air-currents. But the mastery of 
 the air is in reality an achievement of the twen- 
 tieth century. The heavier-than-air craft adopted 
 from the automobile the motive power which has 
 been such a large factor in mankind's most recent 
 major triumph. During the early years of this 
 century experiments were in progress which were 
 to prove epoch-making; however, the desired 
 
MAN UNSHACKLED 5 
 
 stimulus was lacMng. In fact, there still re- 
 sounded tlie persecuting ridicule which was 
 heaped upon Langley during his classic work some 
 time earlier. But the intellects of those perse- 
 yering pioneers, directed by imagination which 
 penetrated the unknown, laid the foundation of 
 that knowledge which was destined to become "the 
 wings wherewith we fly." 
 
 Mankind pays for progress in many kinds of 
 sacrifice. The terrible competition of warfare 
 stimulates effort and forces from the brain of 
 man a flood of ideas and developments which 
 under normal conditions would be spread over a 
 half a century. This is no defense or excuse for 
 war, but amid the wreckage of modem war there 
 is much salvage. It is not a total loss. The "World 
 War bequeathed to the present generation a won- 
 derful heritage — the mastery of the air. When 
 it broke in all its fury it was at once recognized 
 that the airplane injected the third dimension into 
 reconnaissance and that it could be used effec- 
 tively as an offensive weapon. Due to this irre- 
 sistible impetus man thought and worked and took 
 chances. Improvement followed improvement in 
 rapid succession and the uncertain, hazardous 
 plaything of dare-devils in 1914 emerged from the 
 crucible at the cessation of hostilities four years 
 later, a staunch, dependable, highly developed ma- 
 chine adapted to many uses for all mankind. 
 
 The airplane now holds open the doorways of a 
 wonderland to mankind. WiU he enter with see- 
 
6 THE BOOK OF THE SKY 
 
 iiig eyes and open consciousness? It has brought 
 the arctic regions of the upper levels within an 
 hour or so of earthly beings. Man may visit the 
 fairyland of the clouds in a half hour after dinner 
 and enjoy the splendor of sunset tints in this mar- 
 velous gallery of vaporous sculptures. It awaits 
 to take him to those heights from which incom- 
 parable panoramas unfold and melt into distant 
 air, a hundred or two hundred miles away. For 
 the individual who aims to enjoy the fullness of 
 living it has brought two great blessings — ^it has 
 shortened distance and it has lengthened time. A 
 tedious journey is shortened by the speed and 
 directness of air-travel and, although the hands of 
 the clock may describe a lesser angle, this time- 
 interval is greatly lengthened for the conscious 
 and knowing aerial traveler by the intensity of ex- 
 perience which is crowded into it. 
 
 Thus we have passed the verge of one of the 
 greatest triumphs over Nature — one of the great- 
 est strides along the highway of progress. Is 
 there a person who is not stirred to thankfulness 
 for the privilege of witnessing this advent of man- 
 kind into the aerial realm? In fact, the mastery of 
 the air is an achievement which perhaps will never 
 be equaled again when considered from the view- 
 point of the vast variety of experiences it may 
 bring to mankind. Flying is already a common- 
 place experience for many thousands of persons. 
 This generation will see the addition of millions to 
 the ranks of those who have invaded this hitherto 
 
MAN UNSHACKLED 7 
 
 sacred realm; who have drunk deep of its thrills; 
 who have seen its magnificent and awesome sights ; 
 and who have played hide-and-seek with the 
 imaginary fairies of clondland. 
 
 There may be some who would question the 
 statement that man now is master of the air, but 
 mastery like many other terms is a relative one. 
 Mastery of the air is complete for those who have 
 ascended in an airplane at hundreds of feet per 
 minute to, through, and above the lower and in- 
 termediate clouds until more than half the earth's 
 atmosphere lay below them; who on a clear day 
 have seen the horizon of the earth two hundred 
 miles away in all directions ; who have become in- 
 timate with the mechanisms of storms ; who have 
 dodged the wrath of these magnificent phenomena 
 by passing over or around them in the peaceful 
 atmosphere and blue-canopied skies of the remain- 
 ing vast panorama ; who have remained in the air 
 continuously an entire day supported by motive 
 power under their control ; who have made trips in 
 a few hours that would have been next to impos- 
 sible in an equal number of years by earth-travel ; 
 who have climbed into the solitude of space to such 
 heights that most of the earth's haze, and conse- 
 quently most of the brightness of the sky, were 
 below them; who have looked into this almost 
 black sky with the piercing sun boring through, 
 untempered by the void of interstellar space ; who 
 have looked down upon an indistinct earth blurred 
 by sunlit haze and distance ; who have experienced 
 
8 THE BOOK OP THE SKY 
 
 tUe arctic cold of these frigid altitudes; who, 
 through the sheer enthusiasm of the conqueror, 
 have dived and spinned and looped downward 
 through those intervening miles between this 
 world of space and our earthen world to emerge 
 from the clouds and haze to a safe landing. These 
 persons cannot but feel that they are lords of the 
 aerial kingdom and reign unchallenged except by 
 the limitations of earthly materials. Of course, 
 the height to which aircraft may ascend wiU al- 
 ways depend upon the presence of a sufficient 
 amount of air, but there are limitations also to 
 other modes of travel. In fact, aU our past con- 
 quests have their limitations. We daily trust our 
 lives to the strength of steel in railway transpor- 
 tation; we ride at high speed in the automobile 
 trusting to tires, axles, and steering gear ; and we 
 sail the seas with many risks overshadowing. But 
 in these more commonplace activities we feel that 
 we are masters. 
 
 Those whose vocations train them to be ob- 
 servant are universally impressed and depressed 
 by the fact that man is not generally a close or at 
 least not a conscious observer. Along the high- 
 ways and byways of life there is much of interest 
 for the imaginative observer who sees when he 
 looks, but unfortunately few persons see the won- 
 ders and beauties on all sides and still fewer are 
 inspired by them. Settings fuU of wonders and 
 beauty, and situations charged with interest are 
 drab and dull to most persons. "We extract from 
 
MAN UNSHACKLED 9 
 
 a painting or from a sunset, or even from life 
 itself, in proportion to what we put into it. These 
 are merely instruments to play upon; to draw 
 from us something which after being embellished 
 and multiplied is returned to us. And throughout 
 all these experiences the possession of knowledge 
 adds interest to the things which are seen and felt. 
 The air is a new realm except to the few scien- 
 tific men. Its laws, its whims, its pitfalls should be 
 known by the aerial traveler. Pleasure and even 
 safety will depend often upon reading the signs 
 judiciously. Many of the facts of the aerial world 
 are invisible to the eyes because the fluids of the 
 atmosphere are transparent. The winds would go 
 their whimsical way unseen except for their effects 
 upon clouds. They are the ringmasters of the 
 clouds and are made visible by the structures, di- 
 rections, and velocities of these visible vaporous 
 bodies. The clouds thus become the signposts 
 along the highways of air-currents, their ever- 
 changing forms telling the hidden secrets of the 
 winds and even foretelling the aerial conditions 
 which are to come to-morrow. The haze, the sun- 
 set-colors, and the many meteorological facts of 
 altitude, season, and locality combine with the 
 changing scenery of cloudland and the variety of 
 the landscape to provide the observer who sees 
 with more than he needs to occupy him fully; with 
 more emotions and sentiments than his psycho- 
 logical being may accommodate; with more in- 
 spirations than his imagination and finer sensibili- 
 
10 THE BOOK OF THE SKY 
 
 ties may utilize during Ms hours in the air. But 
 in order to experience the fullness of this kingdom 
 he must open his eyes and his consciousness. 
 
 Opening the doorway of his intellect to the won- 
 ders of the sky and of air-travel has another far- 
 reaching practical value. Although flying already 
 may be considered quite safe, the possibilities of 
 accidents are more terrible to contemplate than 
 those attending activities which are not as novel. 
 A busy mind has less time for contemplation when 
 drinking from the perpetual spring of delights, 
 thrills, and inspirations. Mental idleness magni- 
 fies danger, and time for contemplation under- 
 mines the nerves. These could be called to account 
 for robbing many of the full enjoyment of flying 
 and even for wrecked careers and fatalities. 
 Many thousands and perhaps millions of the pres- 
 ent generation to whom flying is still a dreamed-of 
 thrill will, in the next score of years, come to view 
 air-travel as a commonplace event. It will be un- 
 fortunate if these thousands enter the domain of 
 three-dimensional traffic with unseeing eyes and 
 with unresponsive imagination. 
 
 It is one of the aims of this little volume to aid 
 in lifting the veil so that flying, after the initial 
 novelty has vanished, does not become merely a 
 period for contemplating the earth's distance and 
 hardness or merely an interval of speeding 
 through a spacious solitude of void. But how in- 
 adequate are words for describing the poetry of 
 flying ! The masterpiece of painting is only ade- 
 
MAN UNSHACKLED 11 
 
 quately done in pigments, the media for that pur- 
 pose. The author is conscious of the limitations 
 confronting him but he hopes that the treatment 
 from two viewpoints, namely, that of the earthly 
 observer and that of the aerial traveler, will con- 
 vince the reader, regardless of his personal in- 
 terest in flying, that the sky is unexcelled as an in- 
 teresting realm or aspect of nature. Its technical, 
 artistic, and psychological interest is as boundless 
 as itself. These chapters drawn from experience 
 are attempts to interweave some of the wonders, 
 the beauties, the thrills, the emotions, the inspira- 
 tions, the technical facts, of the aerial kingdom in 
 such a manner as to interest the general reader 
 and to aid the aerial traveler to enjoy the wonder- 
 ful heritage of the twentieth century. 
 
CHAPTEE n 
 
 THE COUNTENANCE OP NATUEB 
 
 "To him who in the love of Nature holds 
 Communion with her visible forms, she speaks 
 A various language." 
 
 — ^Bryant. 
 
 THE sky is tlie countenance of Nature upon 
 which, its endless variety of moods and emo- 
 tions is displayed. A clear deep blue sky ex- 
 presses the calm and serenity of content and 
 peacefulness, but with the appearance of clouds 
 Nature awakens and henceforth the heavens ex- 
 press various moods and emotions. When clouds 
 are in the sky Nature may be idle, cheerful, happy, 
 capricious) dull, sullen, angry, or terrible. The 
 moods are often momentary, following each other 
 rapidly and without order, yet at other times they 
 modulate slowly from one to the other, and often 
 their sequence may be predicted. Sometimes Na- 
 ture's countenance may be serene and calm for 
 days as though recuperating from excesses of the 
 deep passion of a summer storm, or it may be sul- 
 len for weeks during midwinter. After a violent 
 destructive blast of a summer storm, how often 
 the sudden cabn and clear sky suggest the youth- 
 
 12 
 
THE COUNTENANCE OF NATURE 13 
 
 ful culprit wlio by a serene countenance pretends 
 that he "didn't do it." As EusMn says, the sky 
 is "almost human in its passions, almost spiritual 
 in its tenderness, almost Divine in its infinity." 
 Surely no other aspect of Nature affords such 
 whimsical, beautiful, and interesting variety as 
 the sky and its clouds. 
 
 The earth's cloak varies from season to season, 
 one aspect modxdating slowly and imperceptibly 
 into another, but the clouds, borne on the winds 
 and modified by them into delicate, intricate, 
 rugged, and majestic forms, will reward the con- 
 scious observer hourly and even momentarily for 
 glancing skyward. Add to the beauty of these 
 modellings, the color effects produced by sun, sky, 
 haze, and shadow, and the heavens framed by any 
 window become a succession of superb master- 
 pieces defying the human genius of the masters 
 who would paint them. Rich indeed is he who 
 possesses the ability to see and to sense these 
 heavenly scenes and whose imagination, ;Tiat di- 
 viae heritage bestowed upon every humaa being, 
 has not been stifled by the ways of modern civiliza- 
 tion. The sky with its expressive clouds is the one 
 charming aspect of Nature which f oUows mankind 
 from the open places to the congested cities. Even 
 the cave-dweller in the metropolis is not denied 
 the beauties of cloudland except by himself. He 
 needs only to lift his eyes and open the doorway 
 to his consciousness. 
 A painting, an interior, or one of Nature's nooks 
 
14 THE BOOK OF THE SKY 
 
 may merely reflect the mood of an individual if 
 that mood is definite and powerful but even such 
 objects and limited environments exert their influ- 
 ence upon the mind. Those possessing finer or 
 more responsive sensibilities usually respond to 
 the mood of their surroundings. But in nearly all 
 cases the extensive sky is master. How often does 
 the individual take his mood from the sky at his 
 first morning view from the window. Who may 
 not respond to the cheerfulness of a fair-weather 
 sky with its peacefully drifting clouds, regardless 
 of the intensity of his mood or passion, if he will 
 give Nature a fair chance? Who is not susceptible 
 to the serenity or languor of the clear unbroken 
 blue canopy of a cahn day? And who has not 
 been depressed by the gloom of the leaden sky of 
 a rainy speU? Under great joy or sorrow Nature 
 may be temporarily defeated but usually the sky 
 with its variety of moods is overwhelming by its 
 infinity. It is not approached in this respect ex- 
 cept perhaps by the sea. Even an expanse of 
 water bounded by the horizon owes its psychologi- 
 cal influence largely to the expression of the 
 canopy above it which is more extensive and more 
 generally expressive. 
 
 It is strange how unacquainted most persons 
 are with the heavens. Nature has done much in 
 this part of creation which may interest, please, 
 and instruct mankind; still the sky is almost ig- 
 nored by the multitude. The veneer of modern 
 
THE COUNTENANCE OF NATURE 15 
 
 civilization lias reduced man's sensibility to the 
 calls of Nature. Modern educational systems do 
 little or notMng toward developing or even main- 
 taining the divine gift of imagination to each 
 child who begins a sojourn in this world. They do 
 not teach the art of observation or the philosophy 
 of life or of living. They ignore a fundamental 
 fact that man extracts from his journey accord- 
 ing to his ability to extract. If Nature would send 
 a storm-cloud occasionally across the sky to water 
 the earth the purely utilitarian purpose of the sky 
 would be satisfactorily fulfilled. One must con- 
 clude when in a fanciful mood, that the beauties 
 and passions of the sky are to please and to in- 
 terest man. 
 
 Nature is bountiful; she usually gives heaping 
 measure. For example, the wonderful gift of 
 color-vision which enables man to see a magical 
 drapery over all creation is merely good measure, 
 for a color-blind mankind could exist without in- 
 convenience and be happy. The sky by its posi- 
 tion is surely meant for all, but how many see its 
 marvels, learn its lessons, or give it thought? How 
 many to-night are able to recall that rugged range 
 of vaporous mountains which floated above the 
 southern horizon nearly the whole afternoon? Do 
 those who saw it remember the delicate pastel tints 
 of its rocHike crests emerging from the deep 
 purple depths of the sea of haze? Bayard Taylor 
 would have seen them — 
 
16 THE BOOK OF THE SKY 
 
 "Bathed in the tenderest purple of distance, 
 
 Tinted and shadowed by pencils of air, 
 The battlements hang o'er the slopes and the forests, 
 
 Seats of the gods in limitless ether, 
 Loomiag sublimely aloft and afar." 
 
 Of the millions of persons who on any autumn 
 evening looked toward the sunset (because it lay 
 in the direction in which they looked), how many 
 consciously saw the yari-colored display with its 
 deep shades of color peculiar to the season? 
 
 If they did see the sunset did they feel the mood 
 of the scene? Did the rose-fringed purple-shad- 
 owed clouds floatiag slowly, tranquil in spirit, in- 
 oculate them with the same restfulness so delight- 
 ful after the day's work is done? Did they, — ^but 
 never mind, for there is no end. 
 
 Those millions who daily ignore the wonders of 
 cloudland will be awakened, to some extent at 
 least, to an appreciation of this fairyland when 
 they visit it in the winged craft which can take 
 them on such a sojourn and return them safely in 
 a brief hour at the end of the day's work. The 
 automobile is still a marvelous recreative agency, 
 for by means of it those imprisoned in congested 
 cities may reach the open, clean, and quiet places 
 in a short time. It has brought the freedom of 
 the country almost to the door of the city apart- 
 ment, but compare this blessing with the mar- 
 velous, almost dreamlike possibilities of the air- 
 plane. It will soon be just as easy to visit the 
 fairylands in the sky after dinner on a summer's 
 
THE COUNTENANCE OF NATURE 17 
 
 day as it is now to visit the country by automobile. 
 It is now just as possible. In a brief space of an 
 hour or so in a powerful aircraft one may enjoy 
 relief from the sweltering humidity of midsummer 
 in the polar climate three or four miles above. 
 Freezing temperatures wiU be found in summer 
 nearly always at altitudes under three miles in the 
 temperate zone. 
 
 WiQ the average person with his scanty or 
 smouldering imagination appreciate the wonders 
 of flying? Will he grasp the opportunities af- 
 forded by modern aircraft? Without imagina- 
 tion, the clouds will be accepted with indifference 
 when among them. To those who see only with 
 their eyes, the clouds of the distant sunset will 
 always be indistinct and insignificant, but to the 
 imagination, which reverses the perspective of the 
 senses, these delicately tinted, pulsating objects 
 will be alive, imposing, kindred spirits, however 
 distant. The sky may be appreciated by anyone, 
 but is best described by the poet. The beauty of 
 the paintings of the sl^ by the masters is one of 
 the most forceful proofs of the beauty and ex- 
 pressiveness of the sky. These efforts of the 
 greatest masters are at best only weak, dull, and 
 lightless ghosts of the originals but even they are 
 ieharming, beautiful, and expressive. What, then, 
 of the originals ! 
 
 In the following lines Coleridge notes the 
 pleasure of using clouds as vehicles for the imagi- 
 nation, — 
 
18 THE BOOK OF THE SKY 
 
 "0, it is pleasant with, a heart at ease, 
 Just after sunset, or by moonlight skies. 
 To make the shining clouds be what you please, 
 
 Or let the easily persuaded eyes 
 Own each quaint likeness issuing from the mould 
 Of a friend's fancy." 
 
 In literature are described many of the im- 
 pressions which the sky and its inhabitants have 
 made upon delicate and attuned human sensibili- 
 ties. The sun, moon, stars, clouds, storms, sunrise, 
 sunset, blue sky, halo, corona, and aurora have 
 all been subjects of poets of verse and of prose. 
 The many allusions by poets to the sky and to its 
 inhabitants lead one to conclude that the sky is 
 as important to poets as to painters. Even in 
 poetry and painting, some knowledge of the facts 
 of the clouds is useful, and both have displayed 
 the results of study. Euskin's discussions of 
 clouds in painting would be greatly condensed, 
 more readable, and more instructive if he had 
 taken the pains to become acquainted with the 
 facts available at that time. Doubtless, the poetry 
 and painting of the future will show the effects 
 of more accurate knowledge and closer acquaint- 
 ance with the clouds gained by the intimacies pos- 
 sible through flying. The influence of aviation is 
 even already slightly felt in such circles, but its 
 greatest effect is doubtless still somewhat in the 
 future, although perhaps not far off. 
 
 The forms of clouds, their groupings, their alti- 
 tudes, their velocities, their relations to each other 
 
THE COUNTENANCE OF NATURE 19 
 
 and to th.e topography of the earth's surface, all 
 these phases and others cannot be fully visualized 
 or appreciated without touring through cloud- 
 land. Views from the earth are always deceptive, 
 being complicated by the effects of perspective 
 and the one-sided view. Obviously, the form of a 
 cloud will be easily and fully appreciated after it 
 is viewed from various sides, — ^below, on its own 
 level, and above. The aerial traveler is often sur- 
 prised and even astonished in his early experi- 
 ences in cloudland by some of the false concep- 
 tions he has formed especially regarding cloud- 
 forms. He soon notes that clouds may be divided 
 into general classes and that altitude gives cer- 
 tain characteristics to them. In general, he con- 
 cludes that clouds become thinner, less massive, 
 more tenuous with altitude just as the density of 
 the atmosphere diminishes with height. He may 
 note that in so far as form is concerned, clouds 
 may be divided into three regions according to 
 altitude, namely, low, intermediate, and high. 
 KJnowlng that clouds owe their forms to air-cur- 
 rents — ^winds, eddies, vertical convection, etc. — 
 he may generalize regarding the relations of these 
 with altitude. But it is well at first to go no 
 further with generalizations because of the com- 
 plexity of the aerial kingdom. 
 
 It is convenient and not without logic to con- 
 sider the three cloud regions mentioned above, 
 and some general characteristics will be noted. 
 In other chapters more details are presented. 
 
20 THE BOOK OF THE SKY 
 
 Several general forms exist in these three regions 
 and, of course, the actual individual forms are 
 infinite in variety. It is this ever-changing form 
 that is so fascinating, but despite this variety, the 
 task of classifying cloud-forms is not hopeless. 
 
 The high clouds, the cirrus and its combination 
 forms are usually out of reach of the aerial trav- 
 eler and at the present time some of them have 
 not been reached by the highest flights recorded. 
 These cirrus clouds are sometimes at such alti- 
 tudes that they would float far above the highest 
 mountain in the world. They are in the region 
 of speeding winds which whip them into streamers 
 and a vast variety of wind-driven shapes. They 
 are often characterized by symmetry of ripples, 
 billows, and curls. They float in the frigid, clean 
 atmosphere and always consist of ice crystals. 
 Sometimes they are so vanishingly thin that they 
 are barely called into existence by the powerful 
 untempered sun which illuminates them. In this 
 clean rarefied atmosphere the blue skylight creeps 
 into their delicate shadows. These tenuous 
 clouds, sometimes vanishingly thin and always 
 wind-swept into ever-changing patterns, are per- 
 haps the most fascinating of the general types of 
 clouds. They are subjects for poets and painters. 
 They are the last bright clouds in the sky after the 
 sun sets, and long after the sun has disappeared 
 from earthly view these wispy veils are immersed 
 in the golden glow of the sun which is just setting 
 for them. Such a sky viewed from the deepening 
 
THE COUNTENANCE OF NATURE 21 
 
 shadows' of twilight on earth is one of the impres- 
 sive moments in the kaleidoscope of the heavens, 
 foT it is a "majestical roof fretted with golden 
 fire." 
 
 The beauties of these tipper clouds do not de- 
 pend upon the colors of sunset although they are 
 greatly enriched by them. Their delicate, chang- 
 ing forms awaken fancies and taunt the master 
 who would paint them. Here the fairies find their 
 filmy veUs, delicate lace, the richest embroidery, 
 and combiaations of these, well becoming them. 
 The halos around the sun and moon are the handi- 
 work of these high thin veUs. 
 
 The clouds of the middle region would likely be 
 characterized by the aerial traveler first, as so- 
 ciable, clannish, or flocking. Cloud-flocks are in- 
 deed found at other altitudes but they are more 
 predominant among the forms of the intermediate 
 clouds than in other regions. They are generally 
 thicker or more massive than the tenuous upper 
 clouds and, therefore, display a variety of light 
 and shade uncommon in the thinner clouds of the 
 high region. However, the forms of the indi- 
 vidual components vary from the thin delicate 
 flakes separated by patches of blue to the fleecy 
 globular masses closely packed. These afford the 
 painter, poet and nature lover, relief from the 
 monotony of the blue. In this middle region there 
 are plenty of other types of clouds including the 
 less varied stratus type which gives rise to co- 
 ronse around the sun and moon, but the groups 
 
%% THE BOOK OF THE SKY 
 
 doubtless will more effectively stir the fancies of 
 the observer and interest the student of clouds. 
 
 The "mackerel" and "billowed" skies of this 
 region are perhaps the only types of clouds be- 
 sides the cumulus clouds of summer that hold the 
 attention of the casual observer sufficiently to 
 enable him to describe them from memory. The 
 symmetry of the flakes or globular masses in lines 
 in one or two directions is too striking to go un- 
 observed. Many fanciful interpretations are 
 possible. The clouds in this region are often seen 
 to evaporate or to grow denser momentarily. 
 This adds to the great variety of the cloud-effects 
 and cloud-forms of the middle region. These 
 flocks or billowed oceans of clouds are among the 
 superb sights in air-travel. On rising to the level 
 of one of these billowy seas of clouds, one may 
 note the minute details of air-currents made 
 visible. Here one sees and feels the full glory of 
 the kingdom of cloudland as he enters the ball- 
 room of the fairies. And to think that mankind 
 can now enter this fairyland and return during 
 the recreation hours of the day! The wings of 
 imagination liave given way to the wings of 
 reality. 
 
 The clouds of the low region which are likely 
 to attract the average person are the heaped or 
 cumulus clouds. These appear to rest on flat 
 shadowed bases and to rear themselves in turbu- 
 lent crests. Fancy makes of these, rocky crags, 
 huge promontories, rugged peaks and ranges. 
 
THE COUNTENANCE OF NATURE 23 
 
 They are perhaps the only clouds generally ob- 
 served. Overhead they appear as fleecy masses, 
 grayed by shadow, not very interesting in pattern 
 but serving to break the monotony of the blue. 
 The fair-weather type saU gently along over the 
 tranquil blue sea of space tinging a lazy mood 
 with some signs of life. The more interesting and 
 striking cumulus clouds are those seen nearer the 
 horizon. At this oblique angle much of the beau- 
 tiful detail of their turbulent crests is visible. 
 Their flat bases rest in the blue haze of distance 
 and the thunderhead rears itself upward some- 
 times above the middle region — as high as the 
 highest mountain. Those underneath see a dark- 
 ening, threatening, frowning cloud advancing with 
 its deluge. 
 
 After such a cloud-mountain or cyclonic storm 
 has borne down and has spent its energy, the 
 scenery or properties are left to be cleared away 
 by the winds. This chaos of cloudland affords 
 both the earthly and aerial observer many splen- 
 did views of various types of clouds and their 
 rapid evolution into different forms. The fogs, 
 the delicate phantom-like scuds, the darkening 
 cumulus clouds en echelon, the leaden skies, all 
 contribute interest and variety and indicate Na- 
 ture's moods to follow. The tall mountain peak 
 in the distance is favored with a sunshade of 
 cloud. At other times this becomes a vaporous 
 cap or mantle. Sometimes a white banner ap- 
 pears to wave from the leeward side of the crest. 
 
24 THE BOOK OF THE SKY 
 
 All these kindle the imagination; each one is of 
 interest and worthy of attention and thought, for 
 it has a cause behind its existence. These are the 
 details that color the monochrome of life of the 
 unseeing into a masterpiece of glorious splendor 
 and untiring variety for the observant whose sen- 
 sibilities are attuned to respond to Nature's ad- 
 vances. 
 
 The sky provides all the moods of Nature which 
 the painter strives to portray and more. The 
 painter's efforts are commendable and enjoyable 
 but he can never do justice to the sky and its 
 moods. He has merely earthly pigments, weak 
 imitations of light, which do not have the strength 
 or range necessary to record the heavens. A 
 painter finds it difficult to represent a horizon 
 blending from the mists into twilight or a moun- 
 tain melting into its shroud of cloud. How can 
 he then hope to represent the white crests of 
 clouds illuminated with untempered sunlight sim- 
 ultaneously with the shadows of his mountains or 
 forests in his landscape? In a similar manner the 
 poet's media are weak and lacking in range and 
 expressiveness, still his descriptions are beauti- 
 ful. Notwithstanding the painter's handicap of 
 earthly pigments which at best can only feebly 
 represent clouds, his canvases are interesting, 
 charming, and beautiful. This testifies to the 
 overwhelming superiority of the originals. Then 
 why not observe and enjoy them and learn their 
 meanings ? 
 
CHAPTER III 
 
 THE FOEMATION OF CLOUDS 
 
 "Aerial spirits by great Jove design'd." 
 
 — Hesiod. 
 
 T^HE multitTidinous forms and varied colors of 
 -*- the clouds not only provide landscapes and 
 seascapes with an ever-shifting scenery to please 
 the eye and to hold its interest, but they teach 
 lessons of winds and weather. Some knowledge 
 of the source, structure, heights and meaning of 
 clouds provides another phase of interest for 
 earthly observers, aerial travelers, and various 
 students of the heavens. Clouds are the visual 
 manifestations of air-currents, for they are 
 modeled and driven by these currents. They tell 
 much regarding meteorological conditions, direc- 
 tion of winds, and to-morrow's weather. To the 
 cloud-wise they reveal something of the tempera- 
 ture and humidity of various regions of the at- 
 mosphere. Knowing their source and their rela- 
 tions to other conditions, such as barometric pres- 
 sure, it is possible to foretell the kind of weather 
 which is likely to be near at hand. Every phase 
 of the weather is commented upon by clouds ex- 
 
 25 
 
26 THE BOOK OF THE SKY 
 
 cepting, of course, clear weather. They play visible 
 parts in the entire pageant of storm from the 
 heralds and banner-carriers of the procession to 
 the straggling rear-guard and those who have lost 
 their way. 
 
 Clouds are formed in clear transparent air by 
 the condensation of the invisible water-vapor 
 which generally exists in the lower atmosphere. 
 Water-vapor is gaseous water and is as invisible 
 and transparent as the air itself. A cloud of con- 
 densed water-vapor consists of minute globules 
 of water. These individual droplets may be said 
 to be transparent, nevertheless they scatter light 
 by reflection just as clear polished glass beads 
 and marbles are seen to do. In such glass spheres 
 the reflection of objects may be seen which indi- 
 cates mirror surfaces and therefore the ability to 
 scatter light by reflection. Another illustration 
 is that of sandblasted clear glass such as a lamp 
 bulb. If this surface be viewed under a micro- 
 scope it will be seen to consist of a vast number 
 of smooth surfaces oriented in a haphazard man- 
 ner just as they happened to be chipped by the 
 sandblast. This magnified roughened glass ap- 
 pears similar to ordinary "chipped" glass. If a 
 sheet of clear glass be finely pulverized the 
 powder is as white as snow and still each minute 
 particle is a clear transparent fragment. All pol- 
 ished surfaces reflect light whether they are trans- 
 parent or not and, therefore, these many trans- 
 parent particles of powdered glass or droplets of 
 
THE FORMATION OF CLOUDS 27 
 
 "water-vapor by reflecting light in all directions 
 give the body a translucent and luminous appear- 
 ance. 
 
 Air is able to hold a certain percentage of water- 
 vapor but its capacity depends upon its tempera- 
 ture. For example, warm air is able to retain a 
 greater percentage of water-vapor or moisture 
 than cooler air. The absolute humidity is the 
 mass of water-vapor contained in a unit volume 
 of air. When a certain volume of air contains all 
 the moisture which it is able to retain at that 
 temperature and pressure it is said to be satu- 
 rated. The relative humidity is the ratio of the 
 actual quantity of water-vapor in a certain volume 
 of air to the total quantity which would be pres- 
 ent if the air were saturated, other conditions 
 remaining the same. The dew-point is the condi- 
 tion when complete saturation is reached, tem- 
 perature and pressure remaining unchanged. The 
 "sweating" of water-pipes, the formation of frost, 
 and the deposition of dew show that atmospheric 
 moisture promptly condenses upon any surface 
 whose temperature is below the dew-point. That 
 is, the cooling lowers the capacity of the air for 
 water-vapor so that some of it must condense. In 
 a similar manner, volume condensation takes 
 place throughout a body of moisture-laden air 
 when it is sufficiently cooled. This cooling can 
 take place by expansion of air when the pressure 
 is reduced such as in an ascending current of the 
 atmosphere, by contact with colder surfaces, or 
 
58 THE BOOK OF THE SKY 
 
 by mixture witK colder air-currents. The result 
 of this condensation is fog or clouds of innu- 
 merable droplets of water or ice particles. Nuclei, 
 such as dust, smoke particles, and electrons seem 
 to be necessary for the condensation of water- 
 vapor. 
 
 The form and altitude of clouds depend some- 
 what upon their mode of formation, that is, upon 
 the manner in which cooling takes place. Fog 
 diifers from cloud only in its location. It is 
 formed by relatively low temperatures near or at 
 the surface of the earth. Clouds are generally 
 produced originally by the cooling of the air by 
 convection currents. These currents are upward, 
 hence, clouds are separated from the earth by a 
 considerable altitude. The final forms of clouds 
 are very much modified after their initial forma- 
 tion by the modeling and even disruptive action 
 of air-currents. When the temperature of the air 
 is below freezing the condensed moisture is in the 
 form of ice crystals but some water-vapor is also 
 present. If such air were carried to higher alti- 
 tudes and mixed with colder air, or cooled further 
 by expansion, some of this remaining water-vapor 
 would condense into ice crystals and thus become 
 visible. These are the important factors in cloud 
 formation, but the details which are definitely 
 known would fill many large volumes. It is not 
 the intention here to give more details than neces- 
 sary to enable the reader to appreciate the inter- 
 esting, useful, and pleasing functions of clouds. 
 
THE FORMATION OF CLOUDS 29 
 
 Clouds do not come from a mysterious source 
 and disappear into another unknown. There is 
 logic and reason behind them. Sometimes they 
 are born hundreds of miles distant in any of the 
 variety of shapes from the towering cumulus to 
 the thin fibrous cirrus. They may be carried on 
 by the winds, buffeted by cross-currents, modified 
 by temperature conditions, altered by the topog- 
 raphy of the earth, disrupted by battling winds 
 and upward currents, finally to evaporate or to 
 spill rain or to float onward after delighting those 
 who lift their eyes to the wonders of the sky. 
 
 Clouds often form before the observer's eyes 
 by the condensation of the moisture in the heavily 
 laden air. For example, the cumulus cloud — ^the 
 product of upward currents induced by the warm 
 earth and lower atmosphere — consists of vapor 
 condensed by expansion or by the colder upper 
 air as it is carried upward. The altitude of the 
 crests of these clouds varies somewhat depending 
 upon the velocities of the individual convection 
 currents. The flat darker bases of the cumulus 
 clouds indicate the altitude above which the con- 
 ditions of humidity, pressure, and temperature 
 are satisfactory for the condensation to take place 
 and below which the capacity of the air for hold- 
 ing water- vapor is not wholly filled. This flat base 
 represents the altitude where the dew-point is 
 reached as the temperature and pressure changes. 
 
 Clouds float in the sky because the individual 
 droplets are so minute that the viscosity of the 
 
30 THE BOOK OF THE SKY 
 
 air is very effective in retarding their fall. They 
 actually would gradually settle in still air, and 
 in general there is always this component inter- 
 mingled with the effects of air-currents. It is not 
 surprising that these minute drops of water float, 
 if one considers other examples. Dust will float 
 in the air for some time before reaching the 
 earth's surface by settling. However, a clod of 
 dirt wiU fall immediately. 
 
 In order to recognize clouds and to discuss 
 their details of formation, structure, and mean- 
 ing, names must be given at least to general 
 classes. They vary in altitude and assume an 
 infinite variety of forms so that it is difficult to 
 choose a simple terminology which adequately 
 meets the requirements. Those who have flown 
 among the clouds and have observed their alti- 
 tudes and forms from all sides should have little 
 trouble in recognizing the various types of clouds 
 from the descriptions which follow. In viewing 
 clouds, the distortion due to perspective should 
 be appreciated and accounted for. For example, 
 the flat dark bases of the cumulus clouds as seen 
 from below make a group of these appear en 
 echelon. The confusion due to perspective is 
 much greater from viewpoints on the earth than 
 in the clouds. 
 
 A condensed form of classification of clouds ac- 
 cording to altitude and form appears to be sat- 
 isfactory for the purpose of this book. For con- 
 yenient reference clouds may be divided into four 
 
THE FORMATION OF CLOUDS 31 
 
 primary and nine secondary forms. These are 
 as follows: 
 
 Primary forms 
 
 Cirrus, or curl cloud 
 Stratus, or layer cloud 
 Cumulus, or wool-pack cloud 
 Nimbus, or rain cloud 
 
 Combination forms 
 
 Cirro-stratus 
 Cirro-cumulus 
 Strato-cumulus 
 Cumulo-nimbus 
 
 Alto forms 
 
 Alto-stratus 
 Alto-cumulus 
 
 Fracto forms 
 
 Fracto-stratus 
 
 Fraeto-cumulus 
 
 Fracto-nimbus 
 
 Several combinations of names are omitted as 
 will be seen on closer study. For example, cirro- 
 nimbus is omitted because rain clouds never have 
 the cirrus form ; there is no strato-nimbus because 
 all rain clouds are flat; fracto-cirrus does not 
 appear because cirrus clouds are always fibrous, 
 broken, and detached ; there is no alto-nimbus be- 
 cause rain clouds are never high. 
 
32 THE BOOK OF THE SKY 
 
 According to altitude clouds may be divided 
 conveniently for many purposes and especially 
 for the aerial traveler. In the classification which 
 follows, those preceded by d are seen most fre- 
 quently in dry weather and are generally separate 
 or globular, or made up of flocks of individuals. 
 Those preceded by w are "wet weather" clouds 
 and are widely extended in form often covering 
 the sky. Altitudes are presented more in detail 
 in later paragraphs. 
 
 Upper clouds, average altitude 30,000 feet. 
 
 d. Cirrus 
 w. Cirro-stratus 
 
 Intermediate clouds, between 10,000 and 25,000 feet. 
 
 d. Cirro-cumulus 
 Alto-cumulus 
 w. Alto-stratus 
 
 Lower clouds, under 10,000 feet. 
 
 d. Strato-cumulus 
 
 d. Cumulus 
 w. Nimbus 
 w. Fracto-nimbus 
 w. Stratus 
 w. Fracto-stratus 
 
 The cumulus, fracto-eumulus, and cumulo- 
 nimbus, all of which are caused by diurnal con- 
 vection, vary in altitudes from a few thousand 
 feet to 25,000 feet so that they are sometimes 
 
THE FORMATION OF CLOUDS 33 
 
 lower and sometimes intermediate clouds, The 
 "dry weather" cumulus is usually a lower cloud 
 with its apex at about 6000 feet and its base at 
 about 4500 feet. The cumulo-nimbus or thunder- 
 storm cloud rears its apex to altitudes from 
 10,000 to 25,000 feet, its base being at about 4500 
 feet. 
 
 These are some of the general facts of clouds 
 and may be sufficient for some readers ; however, 
 more details are found in other chapters. 
 
CHAPTER IV 
 
 THE THUNDEESTORM 
 
 "I wield the flail of the lashing hail, 
 
 And whiten the green plains under. 
 And then again I dissolve it with rain, 
 And laugh as I pass in thunder." 
 — Shelley. 
 
 A MIDSUMMER morning opened dazzlingly 
 bright and very still. The bluish-white sky 
 was bright with the haze of the hot, sultry days 
 of the thunderstorm period but not a cloud ap- 
 peared against this background. There was 
 "green calm" below and "blue quietness" above. 
 It promised to be a duU day for flying for those 
 who yearn for the fairyland of the clouds, but two 
 lords of the air ascend for a trip into their aerial 
 kingdom. The earth below is of interest in its 
 variety of dull colors which become duller or 
 grayer as they ascend, leaving more and more of 
 the sunlit haze beneath them, but this expanding 
 landscape does not compare with the beauties and 
 wonders of cloudland. In the distance the horizon 
 is invisible, the earth is gradually blending into 
 the sky as it is blotted out by the increasing depth 
 
 34 
 
THE THUNDERSTORM 35 
 
 of haze which is encountered in oblique vision. No 
 earth horizon is visible owing to the accumula- 
 tion of smoke and dust-haze carried upward by 
 the convection currents induced by the hot earth 
 below. Then at an altitude of about one mile a 
 horizon appears; it is that of the floating haze 
 and this altitude marks the upper limit of the up- 
 ward diurnal convection air-currents in this case. 
 An unbroken haze horizon presents itself on all 
 sides as though a surrounding sea had been lifted 
 vertically one mile. 
 
 In the distance a few cumulus clouds sleepily 
 rear their cauliflower heads out of the haze like 
 nearly submerged icebergs. In the oblique sun- 
 light the colors of the haze are delicate pastel 
 tints of blue, pink, and purple, but the crowns of 
 the distant clouds are brilliantly yellow-white 
 against the deep blue sky. No upper clouds are 
 present, so the azure canopy is unbroken. The 
 aerial travelers turn instinctively toward these 
 clouds which are poking their heads above the 
 smudge of the earth haze which surrounds their 
 bodies, and steer a course toward one which is 
 energetically rearing itself higher and higher. 
 They are thirty miles away but the aircraft an- 
 nihilates distance at one hundred miles per hour. 
 Eapidly the clouds draw near and soon the ter- 
 rific roar of the aircraft reverberates among these 
 vaporous crags. Upward the craft climbs toward 
 the summit of the thunderhead. Eight, nine, and 
 ten thousand feet are successively indicated by 
 
36 THE BOOK OF THE SKY 
 
 the altimeter and at twelve thousand feet the 
 crown is reached. The flyers pass over it and 
 back through it and wander down the sides in a 
 succession of antics in the exuberance of freedom. 
 Anything to pass the time, for they intend to 
 watch the evolution of a thunderstonn. 
 
 At noon they again find themselves on the cauli- 
 flower crest which has by this time reared itself 
 seventeen thousand feet above the earth's sur- 
 face. Here it stands majestically supreme, a 
 mighty crag of vaporous cloud surrounded by iso- 
 lated miniatures two miles below. It is time for 
 lunch and the fuel is low so the airmen start for 
 their landing field at an easy glide. Minutes pass 
 and the altimeter clips off the thousands of feet. 
 At seven thousand feet the level of the smaller 
 clouds is reached and they look back upon the 
 majestic thunderhead rising two miles above his 
 assembling cohorts. Downward they continue 
 their course and onward to their lunch thirty 
 miles away. On landing, nothing is seen of this 
 group of clouds in the distance except the crest 
 of the thunderhead, a delicate pinkish pastel tint 
 almost submerged by the bluish haze. The lesser 
 depth of haze between its looming crest and the 
 observers does not quite obscure it, but its body 
 and base and the large group of lower minor 
 cumulus clouds near it are in obscurity behind the 
 depths of miles of a midsummer veil of haze. The 
 aerial explorers are not in haste despite their de- 
 sire to see the evolution of a thunderstorm be- 
 
THE THUNDERSTORM 37 
 
 cause they know that on this still day the clouds 
 ■will not travel out of range of their speedy craft 
 and that thunderstorms are most prevalent in the 
 afternoon. They are also fairly certain that this 
 thunderhead will continue its evolution into a 
 thunderstorm because the hot day, the high hu- 
 midity, and quiescent atmosphere are conducive 
 to this end. 
 
 Lunch is over, fuel is supplied to the aircraft, 
 and minor details are looked after but the airmen 
 need not hasten. They find a shady spot and chat, 
 casting occasional glances over the pastel-tinted 
 sky unbroken except in one place near the horizon 
 where their thunderhead is gently floating show- 
 ing its crest faintly through the deep bluish haze. 
 Sometime later the lower sky in this direction has 
 darkened considerably and the explorers don their 
 warm clothing in the sweltering heat, for they are 
 going where the temperature will be near zero. 
 They ascend and in a short time are above the 
 haze. What a change has taken place in their 
 thunderhead ! What a titanic army of clouds has 
 come to reinforce that majestic leader ! The air- 
 craft steadily climbs as it approaches this mass of 
 cloud mountain. At the lower altitudes the real 
 form of this cloudscape cannot be distinguished. 
 Perspective is deceiving and none of the upper 
 surface can be seen. Higher and higher they 
 mount ufitil at ten thousand feet they are above 
 the level of the minor supporting clouds. Fifteen 
 thousand feet is reached and they approach the 
 
38 THE BOOK OF THE SKY 
 
 level of the main body of this tnrbulent mountain. 
 Still the crest of the thnnderhead looms thousands 
 of feet upward. At twenty thousand feet they are 
 above the level of all except the central crest 
 which extends several thousand feet higher. 
 
 What an awesome sight this boiling mass of 
 clouds is to the two hinnan pigmies in their insig- 
 nificant craft ! The mighty thunderhead has been 
 stretched skyward by the powerful upward cur- 
 rents from the hot earth below until from its flat 
 dark base a few thousand feet above the earth to 
 its brilliant cauliflower crest, four vertical miles 
 intervene. Eeinforcements of lesser majesty but 
 compensated for in number are packed closely 
 around the mighty center and are stirring impa- 
 tiently. In this manner the huge restless moun- 
 tain of clouds, whose nucleus is the thunderhead, 
 is built up, recalling to the imagination the solid 
 phalanx of the Greeks surrounding their powerful 
 leader. 
 
 The cloud-mountain, as large as any earthly 
 mountain, is a befitting abode of Jove when he is 
 in a mood for work. Flash ! A lance of blue-white 
 light starts from somewhere in the crest and loses 
 itself in a twinkling in the obscurity of the turbu- 
 lent mass. Jove is at work hurling his thunder- 
 bolts. Could the airmen but stop the roar of their 
 engine in order to hear the thundering accompani- 
 ment of the storm, the awesome spectacle would 
 be complete. 
 
 It is bitter cold at this altitude and as the vapor 
 
THE THUNDERSTORM 39 
 
 of the clouds condenses around the dust or elec- 
 tronic nuclei in the atmosphere, the raindrops thus 
 formed at the lower altitudes are caught in the up- 
 ward surge of the convection currents and are 
 hurled vertically into this cold region. Thus tiny 
 hailstones are born. They fall again outside the 
 boiling center and gather more water only to be 
 caught again at lower altitudes and hurled upward 
 where another layer of ice and snow is added to 
 them. This cycle may be repeated many times 
 before the hailstones fall outside the influence of 
 the storm center to drop to earth and spread de- 
 struction to crops and skylights. 
 
 A thunderstorm is characterized by thunder and 
 lightning but the latter has no influence on its 
 genesis, development, course, or destination. It 
 is merely incident to, or a product of this type of 
 storm. It may satisfy when in a fanciful mood 
 to attribute the source of thunderbolts to Jove, 
 but in reality the source of lightning is still 
 shrouded somewhat in mystery. It is known that 
 lightning is born in the storm but scientists have 
 not explained the mechanism in detaU. A strong 
 upward current of air is a conspicuous feature of 
 the thunderstorm. This is apparent to the aerial 
 observers in the turbulent heads of the cumulus 
 cloud which was the parent of the thunderstorm. 
 This updraft carries raindrops upward if its ve- 
 locity is greater than about eighteen miles per 
 hour because raindrops cannot fall in still air 
 ^nth a greater velocity. This upward rush is 
 
40 THE BOOK OF THE SKY 
 
 strong in this ease as is evident by the high alti- 
 tude of the crest of the storm clonds. HaU is pro- 
 duced by the freezing of the raindrops owing to 
 the frigid temperature which the airmen experi- 
 ence at their high altitude. Air is drifting down- 
 ward in some places because it cannot be rushing 
 upward everywhere. The raindrops which have 
 not been solidified may be torn to pieces by falling 
 and by the upward rush of air. Electric charges 
 are produced by tearing things apart and in this 
 ceaseless turmoil in the thunderstorm the many 
 raindrops torn asunder repeatedly may be the 
 source of the electricity which manifests itself in 
 lightning discharges. This mechanism is hidden 
 from the aerial explorers as well as from the 
 meteorologists on earth, but the airmen see the 
 flashes of lightning repeatedly. 
 
 All this time they are nosing about the thunder- 
 storm at a safe distance in the quiet atmosphere. 
 They approach with the most intense feeling of 
 awe yet encountered in their aerial travel, for 
 there is one of Nature's greatest phenomena of 
 concentrated energy. This mountain of agitated 
 clouds, ever-changing in minor details but main- 
 taining its general form, is watering the parched 
 earth but also intermingling with this good-will 
 the destructive effects of the hailstones and of 
 those bolts of lightning which pass from cloud to 
 earth. Many of the bolts pass from cloud to cloud 
 dissipating their energy in a harmless manner, 
 nevertheless frightening the more timorous of 
 
THE THUNDERSTORM 41 
 
 eartli-beiiigs who look upward at the sligMly un- 
 dulating dark base of tMs vaporous cloud-moun- 
 tain passing overhead. Little consolation do 
 earth-beings find in the fact that lightning picks 
 only three victims yearly out of each million of 
 inhabitants in this country. Those underneath do 
 not realize the majestic form of this thundering 
 cloud which to them is frowning darkly. To them 
 it may even be raining and thundering all over the 
 world. Little do they realize that two human be- 
 ings in a frail craft are four miles above them in 
 the clear sunshine watching the mechanism of the 
 storm from behind the scenes I 
 
 Those relatively few persons beneath the storm 
 who are cloud-wise are not surprised by the thun- 
 derstorm's visit because the humid air and calm 
 hot day warned them of such a possibility. For 
 several hours before the storm came they had been 
 conscious of low-lying cumulus clouds hovering 
 along the horizon. Finally they noticed some of 
 these rocky crests appeared to be rearing higher, 
 partially owing to the illusion due to their ap- 
 proach. The earthly observers did not hear the 
 thunder until the storm drew within fifteen miles 
 but they knew by the dark base that a thunder- 
 storm was moving upon them. "When a strip of 
 bluish white cloud resembling a wreath appeared 
 in front of the approaching mass of clouds they 
 knew that rain would be upon them in about ten 
 minutes. As this squall-cloud approached it drew 
 behind it a broad foreboding curtaiu of cloud 
 
42 THE BOOK OF THE SKY 
 
 from some place below the horizon screening the 
 majesty of the turbulent thunderheads from 
 earthly view. By the unbroken grayness of this 
 extensive sheet the cloud-wise persons knew that 
 a heavy rain was in store. The gentle breeze which 
 had been blowing from the south died down and 
 calm reigned for several dramatic moments fore- 
 telling the imminence of the crash of the storm. 
 Only the faint ominous roar of the approaching 
 squall was heard. Finally, as it struck, the trees 
 bent madly for a few minutes. Suddenly there 
 was a crash of thunder and large drops of rain 
 began to fall as though they had been jarred 
 loose from the clouds above. The action then 
 rapidly hastened to the tumultuous climax of the 
 present moment for those far below the airmen. 
 They are now in the midst of rain, hail, lightning, 
 thunder, and wind. 
 
 The air men withdraw to a distance from the 
 leading edge of the storm and peer downward 
 toward the earth beneath the cloud-mountain. The 
 earth is obscured under the falling rain and this 
 view beneath gives them a glimpse of Nature's 
 frown. The squall-cloud in front of the storm- 
 center is rolling angrily in the shadow of the tow- 
 ering clouds. They know that preceding the ap- 
 proach of this squall-cloud a gentle breeze is fan- 
 ning the earth. As the storm-front approaches, 
 the wind shifts and becomes violent and gusty. 
 The rolling squall-cloud is a manifestation of this 
 wind in the cloud region, but when it has passed, 
 
THE THUNDERSTORM 43 
 
 the wind becomes more gentle. They smile as 
 they think of those beings far down on earth who 
 see nanght but this angry frown. In their imagi- 
 nations they see those who are overtaken by the; 
 storm away from home or office huddled under a 
 convenient shelter protected from the rain and 
 trembling with each peal of thunder. They visu- 
 alize the farmers putting their horses away, some 
 of them berating the rainy day. The fall in the 
 barometer would have told them of the approach 
 of the thunderstorm. How delightfully cool the 
 air is at the earth's -surface, for it has just 
 returned from the heights of the boiling crests 
 in view of the airmen above. 
 
 All this time the aerial explorers are bathed in 
 clear sunlight under a deep unbroken canopy of 
 blue sky. Their attention during these exciting 
 moments has been centered upon this awesome 
 spectacle of turbulent clouds charged with rain, 
 hail, and electricity. They have viewed it from all 
 angles as close as they dared, for a sideslip into 
 this mass would mean destruction to them. They 
 turn from this huge mass of restless energy to the 
 vast panorama surroxmding them. The cloud- 
 mountain which awed them with its power and 
 majestic magnitude dwarfs considerably, for all 
 about them is the vast panorama of clear sky and 
 sunny weather. The storm, great as it is, is but a 
 portion of the panorama. The cheerfulness of the 
 sunlight and blue sky enters their beings. They 
 note the brilliant white surfaces of the stormy 
 
44 THE BOOK OF THE SEY 
 
 cloud-mouiitain and contrast this with the angry 
 frown of the squall-clond showing from beneath. 
 Truly to them clouds have silver linings. Never 
 again on earth will they succumb to the dark sul- 
 len mood of the storm. They smilingly note that 
 Nature is sometimes two-faced, presenting a dark 
 angry frown on one side and a bright silvery smile 
 above. 
 
 The cold has crept beneath their polar clothing 
 so they drop downward to warmer altitudes and 
 investigate the quieter masses of clouds surround- 
 ing the storm-center. The huge cloud-mountain is 
 already disintegrating and the fragments are dis- 
 persing to float away or to disappear according to 
 the whims of air-currents. At eight thousand feet 
 they reach the level of the overcast sky trailing for 
 a distance behind the moving stoAn. They turn 
 toward home with mingled emotions following this 
 full experience with one of Nature's aerial won- 
 ders. They cannot escape an emotion of sheepish- 
 ness, for have they not been spying upon Nature 
 behind the scenes ? Have they not seen that which 
 hitherto has been obscured from earthly view by 
 the dark clouds and rain? Surely mankind is tri- 
 umphing over Nature. 
 
 They approach the field and glide to a landing 
 removing their moisture-laden goggles, which ow- 
 ing to their coldness, condense the water-vapor in 
 this hot region. They remove their high-altitude 
 clothing, sticky with moisture as quickly as pos- 
 
THE THUNDERSTORM 45 
 
 Bible, for the heat is oppressive. As they hasten to 
 a shady spot they are greeted with the remark of 
 an earthly friend, "This certainly has been a hot 
 day and scarcely a cloud in the sky all day long." 
 
CHAPTEE V 
 CLOUD-POKMS 
 
 "Sometimes we see a cloud that's dragonish; 
 
 A vapor sometime like a bear or lion, 
 'A tower 'd citadel, a pendant rock, 
 
 A forked mountain, or Hue promontory 
 With trees upon 't, that nod unto the world, 
 And mock our eyes with air; thou hast seen these 
 
 They are black vesper's pageants." 
 
 — Shakespeee. 
 
 THOSE who are appreciative of only the beau- 
 ties, the witchery, the moods, and the passions 
 of the clouds require no scientific terms for the 
 endless variety of cloud-forms. Their imagina- 
 tions respond with apt names very suitable to 
 their fancy or mood at the moment. However, as 
 the witchery of the clouds enslaves the attention 
 of the observer more firmly, his kindled imagina- 
 tion is interrupted by more and more questions. 
 The fanciful or esthetic mood must occasionally 
 give way to an inquiring mood. The observer 
 finds himself occasionally attempting to answer 
 these questions. He begins to see logical relations 
 
 46 
 
CLOUD-FORMS 47 
 
 between cloud-forms and to note their connection 
 with winds and weather. Unconsciously he has 
 become a student of the clouds. This wiU happen 
 to many who begin by merely opening their con- 
 sciousness to the wonders of cloudland, and this 
 study will serve to increase their interest. There 
 is little danger of scientific interest in the facts of 
 clouds usurping the place of esthetic and fanciful 
 interest and no thoughtful observer of the multi- 
 tudinous formations and the variety of color can 
 escape a longing for some facts and reasons. 
 When he reaches this point he wants names for 
 general forms, at least, to use so that his thoughts 
 and observations may be orderly. The aerial 
 traveler will readily learn to recognize the various 
 types of clouds and will have much advantage over 
 the observer at the earth in intimately examining 
 their forms. To the aerial traveler the multitude 
 of cloud-forms and their delicate details will come 
 to mean more than beauty and prophecy. They 
 will show him some of the intricacies of currents 
 and eddies in the vast invisible sea of air. He will 
 come to bestow upon clouds the additional attri- 
 bute of making the unseen visible. Of course, 
 there are many currents which remain invisible at 
 all times because the conditions are not satisfac- 
 tory for condensation of water-vapor. Science 
 has supplied far more names than one requires for 
 his everyday appreciation and study of clouds. In 
 the following paragraphs will be found brief de- 
 scriptions of the chief characteristics of the prin- 
 
48 THE BOOK OF THE SKY 
 
 cipal elond-forms and some special ones of in- 
 terest. 
 
 Cirrus. These are the highest of all clouds, 
 often at altitudes between 30,000 and 40,000 feet. 
 They assume many forms from the thinnest haze 
 to many detached forms. According to these 
 forms, they may be described as delicate, fibrous, 
 filmy, hairlike, tailed, ribboned, curled, ringleted, 
 feathery, plumed. They are generally white in 
 color but often appear of a yellowish tint in con- 
 trast with the blue sky. Sometimes they are ar- 
 ranged in belts, often like strands of hair or 
 plumes of feathers, nearly always showing the 
 effects of high winds, and by the effect of per- 
 spective, appearing to converge toward points of 
 the horizon. They are frequently the result of 
 cyclonic convections that sometimes extend as high 
 as ten miles. When thus formed they are driven 
 far in advance of the cyclone area and herald the 
 approach of the storm-center or area of low 
 barometric pressure. They are also common in 
 the midst of areas of high barometric pressure, 
 due perhaps to the lifting of the Upper air or to the 
 Gverruiming of the upper air in the general proc- 
 esses of air circulation. They are formed at low 
 temperature often as low as 50° Pahr. which ac- 
 counts for their tenuous character because little 
 water-vapor could be present at these tempera- 
 tures. The strife of the winds and convection cur- 
 rents is responsible for their many characteristic 
 forms. 
 
CLOUD-FORMS 49 
 
 Cirro-stratus. The altitude of these clouds is 
 slightly lower than that of cirrus, at an average 
 elevation of about 26,000 feet. On the approach of 
 the cyclonic storm the cirrus clouds thicken and 
 gradually take the form of a thin white sheet or 
 veil having the appearance of a tangled web and 
 often covering the entire sky. Their origin is the 
 same as that of the cirrus from which they evolve. 
 They generally consist of ice crystals and are 
 responsible for the halos around the sun and 
 moon. 
 
 Cirro-cumulus. Thfese are small globular or 
 fleecy masses or white flakes of cumulus clouds 
 generally at altitudes of 20,000 to 25,000 feet, that 
 is, in the lower cirrus region. They possess very 
 slight shadows and are often arranged in groups 
 and lines. They occur in large numbers and may 
 be described as "curdled" sky or ''mackerel" sky. 
 Their origin is usually due to local convection cur- 
 rents induced by unequal, local heating. For each 
 convective rise of air there must be an equivalent 
 descent, each rise being represented by a small 
 cumulus surrounded by descending air and rela- 
 tively clear sky. 
 
 Alto-stratus. This is a thick grayish or bluish 
 veil or sheet with an average elevation of about 
 13,000 feet. Sometimes it is of a fibrous nature. It 
 goes through the same changes in form as the cir- 
 ro-stratus but its elevation is only about one-half 
 as great. It gives rise to coronse occasionally but 
 not to halos. It may be formed in the air forced 
 
50 THE BOOK OF THE SKY 
 
 upward by converging winds in the storm area of 
 a cyclone, by tbe flow of warmer air over a colder 
 layer, or by the cooling of the humid air due to 
 the evaporation of alto-cumuli. 
 
 Alto-cumulus. These are rather large globular 
 masses, white or grayish and partially shaded, 
 often closely packed in groups or rows which re- 
 semble cirro-cumuli. The detached masses are 
 usually larger and more compact at the center of 
 the group. Those at the center are strato-cumuU. 
 At the margin they form into finer flakes changing 
 to cirro-cumulus. Their average altitude is about 
 13,000 feet, about the same as alto-stratus. They 
 presumably owe their origin to local convection es- 
 pecially in cahn summer weather when the relative 
 humidity is low. 
 
 Strato-cumulus, These are large globular 
 masses or large rolls of dark cloud more or less as- 
 sociated with thinner clouds which together fre- 
 quently form a covering for the entire sky espe- 
 cially in winter. Occasionally the formation as a 
 whole has a wavy appearance. The layer is not 
 thick and often blue sky is seen through the in- 
 tervening spaces. All the varied forms between 
 this and the alto-cumulus are to be seen. It differs 
 from nimbus by possessing a globular, rolling, or 
 wavy structure and also because it is not a rain 
 cloud. In fact, they generally appear in dry 
 weather. Their bases are flat being generally at 
 about the same elevation, from 5000 to 7000 feet. 
 They are formed by vertical convection as is in- 
 
CLOUD-FORMS 51 
 
 dieated, by their rounded tops and flat bases, tbe 
 latter being at the saturation level. 
 
 Nimbus. This is the rain cloud and is a thick, 
 extensive layer of flat cloud from which rain or 
 snow is falling. The average altitude of its lower 
 surface is about 3000 feet. It generally has 
 ragged edges. Through openings in this low; 
 layer, an upper layer of cirro-stratus or alto- 
 stratus may often be seen. It may be produced 
 by the converging in front of cyclonic centers, by 
 upward deflection of winds by land or cold atmos- 
 pheric barriers, or by warmer air underrunning 
 colder air; in other words, by forced convection. 
 Mixture of warm and cold air may have some part 
 in their formation. 
 
 Fracto-nimbus. These are popularly known as 
 "scuds." They are detached fragments, fog-like 
 in appearance, often appearing lighter than the 
 nimbus background. They are usually drifting 
 rapidly at altitudes of 300 to 1000 feet. They 
 seem to form only when a strong wind is blowing. 
 
 Cumulus. These are often called "wool-pack" 
 clouds. They are detached clouds with rapidly 
 changing dome-shaped crests similar to cauli- 
 flower heads. A characteristic of these clouds is 
 the flat base at the saturation level. Its sunlit por- 
 tions are a brilliant white or yellowish white 
 against the blue sky. Their great thickness ac- 
 counts for the beautiful gradations of shading 
 from the dark shadows to the brilliant highlights. 
 The average altitude of the base is about 5000 feet 
 
52 THE BOOK OF THE SKY 
 
 and of the crest about 7000 feet. They are pro- 
 duced entirely by vertical convection currents due 
 to temperature differences, consequently they are 
 frequent in the tropics and over continents of the 
 temperate zone in summer. They appear over land 
 most abundantly in the afternoon and over the 
 sea late in the night. Sometimes they form a 
 coastal fringe which shifts a few miles to sea in 
 the night and a few miles inland during the day, 
 attending the land and sea breeze. They often are 
 to be seen over islands and reefs thus revealing 
 the presence of these while still below the horizon. 
 They have been seen to parallel lakes and large 
 rivers. 
 
 Fracto-cumulus. Often these are undeveloped 
 cumuli appearing somewhat tattered but some- 
 times they are torn from the top of the cumuli. 
 If a towering cumulus is closely watched a thin 
 fragment will sometimes be seen projecting gradu- 
 ally from it. It appears like a banner until de- 
 tached and shortly it will be floating alone. The 
 birth of these fracto-cumuli is one of the interest- 
 ing sights of cloudland. Sometimes as cumulus 
 clouds float in from over a large body of water on 
 a hot day they are quite severely torn by the ver- 
 tical convection currents over the land. The land 
 is hotter, hence the severity of the vertical convec- 
 tion currents which detach pieces of the cumulus 
 thus forming fracto-cumuli. 
 
 Cumulo-nimbus. This is the thundercloud 
 which is the accompaniment of every thunder- 
 
CLOUD-FORMS 53 
 
 storm. It is a cumulus cloud from wMch. rain is 
 falling. Many are sometimes massed in the form 
 of huge mountains, towering majestically as high 
 as 45,000 feet. The base of such clouds resembles 
 the nimbus and is at about the same elevation, 
 usually about 4000 feet. Eising out of this nim- 
 bus is the towering mass of turbulent cumulus 
 clouds around whose peaks there often float false 
 cirri. Sometimes there is a fringed appearance 
 to the edges. Local showers of rain, snow, and 
 occasionally hail fall from this type of cloud. The 
 front of extensive thunderclouds of an approach- 
 ing storm usually appears like a bow-wreath 
 spread across the sky from a view-point on earth. 
 This is sometimes called a squall-cloud. 
 
 Stratus. This is a low horizontal sheet of fog 
 often merging into a nimbus cloud. Its altitude 
 usually varies from 1500 to 3000 feet. Sometimes 
 it is merely a sea-fog drifting over the relatively 
 warmer land. It is often due to a layer of cold 
 air underrunning a layer of warmer air and some- 
 times perhaps to a mixture of relatively quiet 
 layers of humid air of different temperatures. 
 
 Fracto-stratus. As the stratus cloud is shredded 
 by the winds or broken up by the summits of 
 mountains the fracto-stratus is formed. 
 
 It is fascinating and instructive to watch these 
 various cloud-forms evolving from one form to 
 another ; to analyze the different air-currents and 
 to visualize their relative temperatures and hu- 
 midities as the clouds form from the clear trans- 
 
54 THE BOOK OF THE SKY 
 
 parent air or as they disappear by evaporation. 
 Observation and study of cloud-forms and cloud- 
 meanings become even mucb more fascinating 
 through the intimacies gained in flying among the 
 clouds. Cloudland then becomes a fairyland of 
 beauty and interest. 
 
 The types of clouds described in the foregoing 
 paragraphs are sufficient, with their many tran- 
 sitional forms, to meet the requirements of or- 
 dinary cloud study. However, there are a number 
 of special forms which are so characteristic that 
 it is convenient to have names for them. 
 
 Billow clouds. These are sometimes caUed 
 "windrow" or "wave" clouds. They occur in se- 
 ries of bands generally with intervening strips of 
 clear sky. They look like waves or billows on 
 water and are formed in quite a similar manner. 
 They are produced by the flow of one layer of air 
 over another of different temperature, density, 
 and humidity. When one stratum of air flows over 
 another layer of different density or humidity, 
 cloud-billows of great wave length are developed 
 in the same manner that winds produce ocean bil- 
 lows. These billows are often of great depth from 
 crest to trough. Obviously, great biUows may 
 exist unseen in the air unless the conditions are 
 satisfactory for the formation of clouds. As a 
 series of waves develop, the air involved rises and 
 falls and is subjected to alternate heating and 
 cooling, with maximal and minimal temperatures 
 corresponding to the troughs and crests respec- 
 
CLOUD-FORMS 55 
 
 tively. If the humidity is great enough so that 
 the air at the trough is just saturated, moisture 
 •will condense above the trough, namely at the 
 crest. Thus the biUows of air become visible in 
 cloud and the troughs being clear, the strips of 
 blue sky separate the individual waves from each 
 other. It is interesting to note that the billow 
 cloud must be rapidly evaporating on the rear or 
 descending portion of the wave and as rapidly 
 forming on the front or rising portion. This must 
 be the ease inasmuch as the waves or billows are 
 driven onward as they are in water. These bil- 
 low clouds form usually in the lower cirrus region, 
 at 20,000 to 25,000 feet, but they may occur at any 
 altitude. In fact, even surface fogs are some- 
 times billowed as well as the highest cirrus clouds. 
 
 Lenticular cloud. As the name implies, this 
 cloud resembles a lentil in form or its cross-sec- 
 tion is similar to that of a double-convex lens. It 
 is formed by the upward deflection of air by moun- 
 tain peaks and possibly by rising air-currents. The 
 low temperature of the peak itself doubtless plays 
 a part. The cloud particles are rapidly evapo- 
 rated as they are carried away by the wind but 
 this loss is constantly being replenished. This, 
 then, is a stationary cloud which is constantly 
 being renewed. It, like many other clouds, is per- 
 manent in quite the same sense that a cataract 
 in a stream is permanent through the continuous 
 supply of water by the source and stream above. 
 
 Crest cloud. This is formed by the upward de- 
 
56 THE BOOK OF THE SKY 
 
 flection of wind by a long mountain range and 
 often covers tlie upper slopes and the top. It 
 appears as a crest cloud only to those in the low- 
 lands, for it is designated as fog by those living 
 in it. This is, of course, quite natural. The main- 
 tenance of this cloud is similar to that of the len- 
 ticular cloud. 
 
 Banner cloud. This resembles a white banner 
 floating from a high mountain peak. The same 
 effect may be seen occasionally in the case of the 
 towering cumulus or cumulo-nimbus. When the 
 winds are strong the pressure to the leeward of a 
 mountain peak is somewhat reduced just as the 
 wind blowing across a chimney-top reduces the 
 pressure in the chimney. This reduction of pres- 
 sure results in a lower temperature. When this 
 temperature is below the dew-point in this some- 
 what rarefied pocket, condensation takes place. It 
 is seen that this cloud is being renewed constantly 
 on the windward side as it evaporates on the lee- 
 ward. 
 
 Scarf cloud. Occasionally as a cumulus cloud 
 rises rapidly due to powerful vertical convection 
 to a great height, a thin cirrus-like cloud, convex 
 on the upper surface, forms above the cumulus 
 crest. At first this appears to be entirely detached 
 but later as the cumulus continues to rise, this 
 cloud extends more and more, finally resting upon 
 the crest and later draping over the sides of the 
 cumulus. It resembles a silken white scarf or 
 mantle. It is due to elevation, expansion, and 
 
CLOUD-FORMS 57 
 
 cooling of the air above the rising cumulus. Gen- 
 erally the elevating of this tipper air does not 
 result in the formation of cloud; however, when 
 there is a thin stratum of nearly saturated air in 
 which an alto-stratus may form when it is lifted 
 bodily by the rising cumulus, the scarf cloud re- 
 sults. If this stratum of saturated air is thin the 
 cumulus cloud may rise far above it. The rela- 
 tion of clouds with clouds is even more interesting 
 than the association of clouds with mountains. 
 
 False cirrus. This name is applied to those 
 clouds combed out from the towering thunder- 
 heads by the high winds of the upper regions. De- 
 spite the comparative calm of lower altitudes 
 when cumuli are conspicuous, it occasionally hap- 
 pens that a towering cumulus reaches an altitude 
 of high wind-velocity. The crest may be drawn 
 out into fibrous wisps of ice crystals. This is a 
 real cirrus cloud from all viewpoints except, per- 
 haps, its manner of origin from which the name 
 is derived. 
 
 Mammato-cumulus. When the base of a cloud 
 shows downward projection bosses, the prefix,' 
 mammato, may be used. Sometimes such clouds 
 are called pocky-cloud, sack-cloud, festoon-cloud, 
 rain-ball, draped-veil cloud. The individuals of 
 a group of these resemble in shape small reversed 
 cumuli. This formation generally occurs in con- 
 junction with a severe thunderstorm in a cumulo- 
 stratus or an alto-stratus cloud. This unusual 
 formation may result from a cold layer of snow 
 
58 THE BOOK OF THE SKY 
 
 (for hail and snow often oeeiir in the upper por- 
 tions of towering cumuli) drifting out over a 
 stratus cloud. This cool layer may descend at 
 many places and each of these descents wUl pro- 
 duce a sag in the base of the stratus cloud. 
 
 TornadOi This cloud, which makes it possible 
 to see the whirlpool of winds comprising this ter- 
 rific storm known as the tornado, is character- 
 istically funnel-shaped. It appears to be an exten- 
 sion of a cumulo-nimbus and is produced by the 
 cooling due to the expansion which results from 
 the rapid rotation of air in the funnel. The veloci- 
 ties of the air in parts of this funnel are said to 
 attain the value of 500 miles per hour. It is a 
 storm peculiar to the United States and most 
 prevalent in the middle west. This cloud fortu- 
 nately is rare for a given locality but when once 
 seen with its attendant destructive power, it in- 
 stills an awesomeness or terror which impresses 
 the picture upon the mind for a life time. It is 
 the smallest, briefest, and fiercest of storms. 
 
CHAPTER VI 
 
 BEYOND AN OVERCAST SKY 
 
 "There the sea I found 
 Calm as a cradled child in dreamless 
 slumber hound." 
 
 — Shelley. 
 
 YESTERDAY thin fibrous clouds barely show- 
 -'- ing against tbe blue came out of the west and 
 passed rapidly on the highways of the winds 
 across the heavens. In the course of an hour they 
 spread across the sky like silken white tresses 
 blown in the wind. These are the "mare's tails" 
 of the landsman and the "cat's tails" of the 
 mariner. Owing to perspective they appeared to 
 spread upward and outward from a source below 
 the western horizon, but this was an illusion, for 
 they were practically at a uniform level. They 
 were the high cirrus clouds which are born in the 
 cradle of a cyclonic storm and go forth driven by 
 the high winds of their altitude to foretell the 
 approach of the storm-area. Over in an adjacent 
 territory, perhaps hundreds of miles to the west, 
 there is an area of low barometric pressure. This 
 is the center of the region of the cyclone — a sys- 
 
 59 
 
60 THE BOOK OF THE SKY 
 
 tern of winds surrounding this low-pressure area. 
 This cyclone is ordinarily very extensive, its di- 
 ameter averaging about 1500 miles. Strong 
 winds and heavy precipitation are associated with 
 this area of low barometric pressure. The filmy 
 cirri owe their origin to the vapor-laden air which 
 is sent to high altitudes by the strong updraft or 
 convection currents in the rainy portion of the 
 cyclonic areas. This moist breath often reaches 
 /altitudes as high as seven miles where the tem- 
 perature may be as low as 50° Fahrenheit, below 
 zero, hence the cirrus clouds always consist of ice 
 crystals. Their tenuous character is due to the 
 fact that little moisture can reach such altitudes. 
 Having been thus formed, they are carried for- 
 ward at a tremendous speed, for the velocities of 
 the winds at these high altitudes are -sometimes 
 as great as two hundred miles per hour. Thus 
 these thread-like streamers bom in the storm- 
 area, herald the approach of the storm itself many 
 hours before it arrives, for the cyclone travels at a 
 much slower velocity, ranging from twenty to 
 thirty miles per hour. 
 
 As time elapses after the first appearance of 
 these messengers speeding on the winds, the 
 clouds gradually become denser and denser. To 
 those skilled in reading the weather-signs, a gen- 
 eral rain or snow is almost a certainty in from ten 
 to thirty hours. These fihny cirri appeared yes- 
 terday so it is not surprising that to-day dawned 
 rainy and dreary. The ground is saturated, rain 
 
BEYOND AN OVERCAST SKY 61 
 
 is drizzling, the ghostly scuds are rapidly drifting 
 beneath the heavy nimbus at an elevation of a few 
 hundred feet. The aircraft with its delicate wings 
 is snugly housed and two airmen sit in the door- 
 way discussing the weather prospects, Above that 
 dark heavy layer of cloud, extending as far as the 
 eye can see, are blue sky and sunny weather. 
 Again Nature has imprisoned mankind under- 
 neath a damp dark blanket and has arranged for 
 a dreary day. The airmen are restless ; they re- 
 sent this tyranny. Scanning the sky carefully 
 they note in the distance a lighter area which sug- 
 gests a stairway to the sunny roof. To reach it 
 means a somewhat hazardous flight at an elevation 
 of less than a thousand feet and some of the dis- 
 tance is over a large area of water. Is it worth 
 the risk to climb this stairway to the freedom of 
 space and sunny weather? They agree that it is; 
 the aircraft is drawn from its snug hangar, and 
 the engine is warmed up in the misty air. Every 
 precaution is taken, for the motive power must 
 not fail in the pinches ahead. They take-off and 
 in a few moments are among the scuds. In order 
 to gain the safety of as much altitude as possible 
 they climb to the base of the apparently infinite 
 area of the dark nimbus cloud and head in a 
 straight line for the brighter spot hoping that they 
 will be greeted by the blue sky above. They fly so 
 close to this dismal ceiling that at times the earth 
 is blotted out by its clammy fringes, but onward 
 they go by the compass toward their promising 
 
62 THE BOOK OF THE SKY 
 
 doorway. They arrive and find an open space, but 
 what a distance to the sky ! They enter and begin 
 their winding climb, for the hole is not large. For 
 fifteen minutes they mount up and up this winding 
 stairway which proves to be one mile in depth. 
 
 They emerge in dazzling sunlight above a layer 
 of cloud a mile in depth and spreading in all di- 
 rections as far as the eye can reach. Continuing 
 their way upward, this jagged surface unfolds be- 
 fore them apparently to infinity on all sides. It 
 resembles a polar sea of snow and ice. Even the 
 pressure ridges are present and it is as white and 
 bright as the purest snow. If it were not for the 
 roar of the engines they might even expect to^ 
 hear the grinding and booming of the pressure 
 ridges of arctic ice. Above them is the dark blue 
 of a dust-free sky. Byron might have been de- 
 scribing this when he wrote, — 
 
 "And they were canopied by the blue sky, 
 So cloudless, clear and purely beautiful, 
 That God alone was to be seen in Heaven." 
 
 This sentiment and mood is appropriate, but that 
 deep, quivering, transparent void of penetrable 
 space is so blue that one desires to repeat and 
 repeat with Southey, "Blue, darkly, deeply, beau- 
 tifully blue. ' ' In this trembling transparency it is 
 easy to imagine faint veiled vestiges of dark 
 vapor intermingled with spots of deceiving light 
 which give to this infinite solitude as seen from 
 above the smudge of the lower atmosphere, a vi- 
 
BEYOND AN OVERCAST SKY 63 
 
 brating depth never represented by the master in 
 flat dead color. 
 
 The sun is radiantly bright, — "God's crest 
 upon His azure shield, the Heavens." The entire 
 earth is shut out below them hidden under a deep 
 vaporous blanket, glowing with intense brightness 
 above but as dark as rain clouds can be on the 
 lower side. What a contrast between the earthly 
 world and that of the airman! The dark ultra- 
 marine canopy overhead is unseamed by even the 
 faintest cirri. It expresses the serenity of the 
 solitude of space. How the airmen long to quiet 
 their craft in order to feel this utter silence ! The 
 engine's roar is greatly decreased by throttling 
 the fuel but the whir of the wires and struts of 
 the gliding craft is loud in this solitude whose 
 silence is expressed by the blue quietude above 
 and the white cahn below. They wish for a balloon 
 and its comfortable basket, commonly disdained by 
 them, for here is its ideal place. It would be 
 heavenly to drift in the sunlight amid the absolute 
 silence. 
 
 The airmen circle about the opening of their 
 stairway as they mount higher and higher. At 
 ten thousand feet they still see an endless ocean 
 of snow-white cloud below them unbroken except 
 for their stairway to earth. They fly here and 
 there but return often not without anxiety to their 
 exit, for it must not close up. If it did they would 
 be in a serious plight, for to bore down blindly 
 through a mile depth of cloud which reaches 
 
64 THE BOOK OF THE SKY 
 
 witMn a thousand feet of the earth would he full 
 of hazards with the odds against them. An air- 
 plane requires little attention to keep it on an 
 even keel. The pilot uses the horizon, whether 
 land, sea, cloud, or haze, for the purpose of main- 
 taining an even keel. This is done as subcon- 
 sciously as the autoist manipulates the steering- 
 wheel and keeps in the roadway. But when the 
 pilot has no horizon and is in blinding cloud or 
 fog, his sense of balance fails him. Gravity still 
 operates, but the lack of uniform velocity of the 
 airplane under the conditions of flying in absolute 
 darkness or in a dense cloud makes instruments 
 such as levels almost useless. If the airplane 
 turned over so that it were gliding upside down, 
 the airman would know this by the rush of blood 
 to the head or by the consciousness of hanging by 
 the belt. Under these conditions where no horizon 
 or other definite reference line or point is avail- 
 able, the airman knows when he is upside down but 
 not when he is right side up. On descending 
 through a deep layer of cloud such as this overcast 
 blanket, the craft might emerge from the lower 
 side in a dangerous position at a terrific velocity 
 and insufficient altitude would remain for gaining 
 control over the craft. The airmen know fully 
 well the danger which would confront them if their 
 exit should close and they are ready to "spiral" 
 downward hastily or even to nose-dive a few 
 thousand feet if the urgency should require it. 
 The exit shows no signs of closing so they con- 
 
BEYOND AN OVERCAST SKY 65 
 
 tinue their circling in this strange world. They 
 catch a glimpse of their shadow cast upon the 
 brilliant white surface below them. It is not an 
 ordinary shadow, for it is fringed with rainbow 
 colors. What a beautiful phenomenon ! They are 
 ready to believe that they are in dreamland or in 
 the land of Jules Verne where multi-colored halos 
 or aureoles might be commonplace adornments for 
 lords of the aerial kingdom. But one of them 
 recollects that back in his past when he was taught 
 physics he acquired the information that such a 
 phenomenon was the result of diffraction or re- 
 fraction of light under certain proper conditions. 
 It then occurred to him that tourists in Switzer- 
 land arise very early in the morning at a certain 
 place in order that they may stand on the eastern 
 side of a valley at sunrise and see, cast on a fog- 
 bank, their elongated shadows fringed wiih rain- 
 bow colors. 
 
 This shadow is the only moving thing in the 
 entire panorama, for the slow movements of the 
 jagged surface of the cloud layer below are not 
 apparent owing to the speed of the aircraft. The 
 scenery is monotonous but the mood is hypnotic. 
 It is difficult to force a withdrawal from this sunny 
 though inexpressively unreal world to that dreary 
 one hidden beneath. However, all this time the 
 extensive blanket of clouds has been drifting and 
 the cloud-lined stairway by this time might emerge 
 miles away from safe landing, so they reluctantly 
 glide toward their exit. They dip into it and 
 
66 THE BOOK OF THE SKY 
 
 rapidly descend in a close "spiral." The field is 
 ten miles away in the murky distance and the air 
 is saturated with chilly dampness. In a few min- 
 utes they glide to earth splashing through water 
 puddles, and stop before the hangar. The faith- 
 ful craft is snugly housed again and the two air- 
 men seat themselves in the doorway. The earth 
 is wet and dark and dreary but they are living in 
 their imaginations in that sunlit blue-canopied 
 solitude a mile or more above them. 
 
CHAPTER VII 
 
 CLOUD-LEVELS 
 
 "I am the daughter of Earth and Water, 
 And the nursling of the Sky; 
 I pass through the pores of the oceans and shores; 
 I change, but I cannot die." 
 
 SHiaiiLET. 
 
 THHE observer of the sky learns by the forms, 
 -»• velocities, and various characteristics of 
 clouds to judge their levels and instinctively he 
 relates to the various distinctive cloud-levels cer- 
 tain patterns, sky-moods, types of beauty, and ap- 
 proaching weather conditions. The observant 
 aerial traveler through the accumulation of ex- 
 periences during his more intimate associations 
 with the clouds learns all these things more 
 definitely. Clouds may mean joy, danger, or even 
 disaster to the airman, therefore he is forced to 
 consider them. He instinctively learns to expect 
 certain formations at various levels ; to judge the 
 extent of the cloud-mass which he may be ap- 
 proaching; to visualize the air-currents from 
 cloud-forms ; to estimate temperatures at various 
 levels to some extent by the positions and forms of 
 
 67 
 
68 THE BOOK OF THE SKY 
 
 clouds ; to judge the thickness of a layer of clouds 
 which may be below him; and to some extent to 
 ascertain whether he is over land or sea or to 
 judge the chorography of the region below him by 
 the character of the clouds and fogs. All aerial 
 travelers will not be so observant as to become 
 skilled in interpreting the clouds but those who 
 would become learned in the ways of the aerial 
 world will observe these sign-posts on the aerial 
 highways and learn their meanings. They will 
 thus become proficient in interpreting the lan- 
 guage of clouds. 
 
 Clouds exist at various times throughout the 
 entire space from the surface of the earth to an 
 altitude of seven miles. On rare occasions they 
 have been observed to be as high as ten miles. 
 Furthermore, they speed along borne by winds 
 ranging in velocity as high as two hundred miles 
 and even more per hour. But notwithstanding this 
 apparent chaos there are laws for them and order 
 among them which the aerial traveler will be able 
 to detect and to utilize. Suppose that all. the 
 clouds of a given season could be recalled to their 
 places. Then the seven-mile layer of atmosphere 
 would be perhaps nearly an unbroken mass of 
 clouds, but if the density could be measured 
 throughout the entire range of altitude, certain 
 defined levels of maximum density would be 
 found. Instead of depending upon this impossible 
 expedient, the regions of maximum and minimum 
 cloudiness may be determined approximately by 
 
CLOUD-LEVELS 69 
 
 observation during many successive journeys in 
 cloudland, but better still, by grouping and aver- 
 aging the cloud data whicb have been systemat- 
 ically recorded by meteorologists. It is of sufficient 
 importance and, it is hoped, of enough interest to 
 present a discussion of cloud-levels. In a way, 
 the discussion will be a summary of certain as- 
 pects of clouds grouped in a manner to obtain an- 
 other view of clouds, their courses, forms, heights, 
 and meanings. 
 
 By tabulating the frequency of appearance of 
 various clouds with reference to altitude, season, 
 and locality, the regions of maximtun and mini- 
 mum occurrence are obtained. In general, a con- 
 dition which tends to increase the relative humid- 
 ity also tends to lower the cloud-levels. For this 
 reason, the various types of clouds are generally 
 lower over sea than over land, lower over humid 
 regions than over large deserts, lower in winter 
 than in summer, and lower at high latitudes than 
 at those nearer the equator. 
 
 If a cloudy day could be made to order in a 
 middle latitude such as that of the United States 
 during which the general types of clouds were dis- 
 tributed according to elevation and density in a 
 manner to represent a true average condition, the 
 airman would find definite cloud-levels if he were 
 able to explore a vertical section of the atmos- 
 phere throughout its extent to an elevation of 
 seven miles. The airman as he ascended on this 
 flight would record the following approximate ele- 
 
70 THE BOOK OF THE SKY 
 
 vations pertaining to maximum and minimum 
 cloudiness : 
 
 'K maximum, — fog level, at or near earth's surface. 
 A minimum, — scud region, up to 1000 feet. 
 A maximum,— cumulus level, about 5000 feet, 
 A minimum, — intercumulus region, 8000 to 12,000 feet. 
 A maximum, — alto-cumulus region, 13,000 feet. 
 A minimum, — alto-stratus region, 13,000 to 19,000 feet. 
 A maximum, — cirro-stratus level, about 26,000 feet. 
 A minimum, — intercirrus region, 28,000 to 31,000 feet. 
 A maximum, — cirrus level, about 33,000 feet. 
 A minimum, — ^the stratosphere or isothermal region, 
 above 36,000 feet. 
 
 Ovdng to the fact that it is generally easier to 
 determine the elevation of maximum and mini- 
 mum cloudiness, the former are expressed as 
 "levels." Between these "levels" lie the "re- 
 gions" of minimum cloudiness. 
 
 The foregoing makes it easy to visualize the 
 general disposition of clouds throughout the 
 seven-mile depth of atmosphere which is inhabited 
 by them. It is seen that there are five levels of 
 maximum cloudiness between which, and above 
 the last level, five regions of minimum cloudiness 
 are interspersed. This mental picture is of in- 
 terest as a whole but it appears of interest to dis- 
 cuss each level or region even at the risk of some 
 slight repetition of portions of other chapters, be- 
 cause each has its ovm characteristics. These fur- 
 ther details should aid the traveler in cloudland 
 to understand its ways. 
 
CLOUD-LEVELS ^1 
 
 Fog level. A fog is a cloud on earth and differs 
 in general from a cloud only in its location. It 
 is formed in two ways as will be seen. It often 
 forms along lakes, rivers, and creeks and even in 
 streamless valleys, on calm, clear nights especially 
 in autumn. During a caJm day the lowest stratum 
 of air has accumulated much water-vapor, and ow- 
 ing to the calmness much of this air remains in its 
 low position after nightfall. This humid air and 
 the earth beneath radiate heat to space owing to 
 the clearness of the sky during the calm clear 
 night and when the air loses sufficient heat to 
 lower its temperature below the dew-point, the 
 water-vapor condenses on the dust particles and 
 a fog results. Such a fog is not likely to form on 
 a cloudy night because the air will not ordinarily 
 cool sufficiently. On windy nights the humid layer 
 is mixed with dryer layers decreasing the result- 
 ant humidity; furthermore, the air is not liable 
 to remain for a sufficient period over a cold sur- 
 face to have its temperature decreased to the dew- 
 point. 
 
 Another general mode of formation is by the 
 drifting of humid air over a cold surface and being 
 cooled by loss of heat to that surface. When 
 cooled sufficiently so that the temperature of the 
 air is below the dew-point, a fog results. The 
 effect of air-currents operates on small and large 
 scales. Fogs may trail along a river or valley or 
 may cover a lake. On a larger scale fogs are pro- 
 duced by ocean breezes blowing over areas of ice 
 
72 THE BOOK OF THE SKY 
 
 and snow. If humid air over a warm ocean cur- 
 rent, such, as the Gulf Stream, be diverted over a 
 colder surface, some of its water-vapor wiU be 
 condensed and an extensive fog will be the result. 
 
 From such a knowledge it is often easy to ac- 
 count for the formation of clouds in the various 
 strata of atmosphere far above the surface of the 
 earth because the same processes take place in the 
 formation of clouds. Furthermore, the airman 
 may be able to judge the topography of the earth's 
 surface when obscured by fog, and perhaps accu- 
 rately to guess the presence of a lake or river 
 which he may be anxiously waiting to "pick up." 
 
 Scud region. The lowest level of maximum 
 cloudiness being at the earth's surface and the 
 next level at approximately 5000 feet, the approxi- 
 mate average elevation of the base of cumulus 
 clouds, the intervening region is one of minimum 
 cloudiness. The elevation of the actual "mini- 
 mum" would be just above the highest fog. The 
 name "scud region" may be logically applied be- 
 cause the "scud" is the only frequenter of this 
 region with the exception, perhaps, of the lower 
 portions of nimbus clouds. 
 
 Cumulus level. The foul-weather type of cumu- 
 lus, including the cumulo-nimbus, is produced by 
 vertical convection currents. The clouds do not 
 form until the humid air reaches elevations above 
 the saturation level; that is, until the point is 
 reached where the air is cooled below its dew- 
 point. This level is denoted by the flat bases of 
 
CLOUD-LEVELS 73 
 
 tlie cumulus clouds. If the clouds drifted or 
 settled below this level they would simply evapo- 
 rate. In fact, these clouds are continually evapo- 
 rating and are being replenished from below. The 
 vertical convection is usually due to air being 
 warmer and therefore lighter than surrounding 
 air. As this humid air expands it cools below the 
 dew-point and is further cooled when the water- 
 vapor condenses. These clouds do not extend as 
 high as the fair-weather types which are formed 
 from air in which the relative humidity is low. 
 The bases of foul-weather cumulus clouds are at 
 an elevation of approximately 5000 feet and their 
 crests at approximately 7000 feet. This is the 
 second level of maximum cloudiness. 
 
 Intercumulus region. This region is that 
 bounded by the foul-weather cumulus level below, 
 and by the fair-weather cumulus, or alto-cumulus 
 level. It lies approximately between 8000 and 
 12,000 feet. 
 
 Alto-cumvlus, level. This is the level of the 
 fair-weather cumulus clouds which are formed 
 during fair, calm summer weather by strong ver- 
 tical oonvection currents. Owing to the low rela- 
 tive humidity and strong convection, the water- 
 vapor does not condense until a generally higher 
 elevation is reached than that sufficient for the 
 formation of the foul-weather cumulus clouds. 
 Hence the alto-cumulus clouds are approximately 
 at a level of about 13,000 feet, which is the third 
 level of maximum cloudiness. 
 
74 THE BOOK OF THE SKY 
 
 Alto-stratus region. This region is botmded by 
 the level of the alto-cumulus clouds below, and 
 above by the level of the cirro-stratus clouds, 
 hence it lies approximately between elevations of 
 13,000 and 19,000 feet. The scarcity of clouds in 
 this region is due to several reasons. It is above 
 the level of diurnal convection currents; hence, 
 practically no cumulus clouds are formed in this 
 region. Many clouds are born in cyclone areas but 
 those of this intermediate level are not distributed 
 as rapidly or as widely as the cirrus clouds owing 
 to lower velocities of the winds in this region than 
 in the region of the cirri. During the periods of 
 anticyclones the air in this region is usually dry, 
 hence no clouds are formed. 
 
 Cirro-stratus level. This is the fourth level of 
 maximum cloudiness or cloud-frequency with an 
 average elevation of about 26,000 feet. The fre- 
 quency of clouds at this level is due chiefly to the 
 high winds which distribute far and wide these 
 clouds which are born in the cradle of the cyclonic 
 storm center. 
 
 Intercirrus region. This region is bounded be- 
 low by the foul-weather cirrus clouds formed in 
 the cyclonic area, and above by the fair-weather 
 cirrus clouds. The average elevations of these 
 two types of cirrus clouds are approximately 
 26,000 and 33,000 feet respectively, so that this 
 region may be considered to lie, say, between 
 28,000 feet and 31,000 feet. 
 
 Cirrus level. This is the fifth and highest level 
 
CLOUD-LEVELS 75 
 
 of maximum cloudiness or cloud-frequency. Dur- 
 ing fair weather, filmy cirrus clouds form at the 
 high, altitudes below the stratosphere due to the 
 cooling of this upper atmosphere which accom- 
 panies a high barometric pressure. Their average 
 altitude is about 33,000 feet, hence this is a level of 
 maximum cloudiness. 
 
 The stratosphere. Above the level of the high- 
 est cirrus clouds very little water-vapor exists. 
 This is the region beyond any appreciable con- 
 vection; hence, clouds seldom form in this region 
 which lies beyond an elevation of about 36,000 
 feet for middle latitudes. In the portion of this 
 region which has been explored by means of re- 
 cording instruments carried by small balloons 
 filled with hydrogen (up to about twenty-two 
 miles) the temperature appears to be nearly con- 
 stant; that is, it does not decrease appreciably 
 with altitude. 
 
 In the foregoing descriptions the altitudes are 
 only approximate, for it is impossible and fortu- 
 nately unnecessary to reduce the levels to a very 
 exact figure. The descriptions as given serve the 
 purpose of this chapter which aims to present an- 
 other vie\vpoint pertaining to the appreciation, 
 study, and interpretation of clouds. 
 
CHAPTER Vm 
 
 MINGLED MOODS 
 
 "Clouds on clouds, in volumes driven, 
 Curtain round the vault of heaven." 
 
 — Thomas Love Peacock. 
 
 IT is one of those occasional days when Nature 
 seems to be uncertain of purpose. For a time 
 a scowl passes over her countenance and gusts of 
 angry rain fall, then as if weakening in her reso- 
 lution, she draws the dark curtain apart and the 
 sun smiles through. Yonder, thin, pale, fragmen- 
 tary clouds, torn by the gale from the nimbus 
 which hangs over the west, are speeding down the 
 wind. Passing successively in shadow, diffused 
 light, and direct sunlight, these wind-blown frag- 
 ments appear like moving opals. To the east are 
 brighter fracto-cumulus clouds like tufts of wool 
 torn by the winds. Far above them is a billowed 
 layer with patches of deep blue sky showing in 
 the interstices. As the fracto-cumulus clouds are 
 driven before the wind, the succession of lights 
 and shadows cast by the billowed stratum upon 
 them give to them a changeableness in light, 
 shade, and tint befitting the mingled moods of the 
 
 76 
 
Z 
 
 
MINGLED MOODS 77 
 
 whole sky. Above all these, streaks of cirrus or 
 cirro-stratus clouds are visible here and there. 
 The movements of these various clouds at differ- 
 ent velocities and in several directions combined 
 with their ever-changing tints and brightnesses 
 give to the sky the appearance of a huge stage 
 amid the excited haste of preparation for a per- 
 formance or of the clearing after one. But from 
 the weather reports no general storm is brewing. 
 Nature is merely indulging in a playful mood, 
 doing this moment and that just what her tem- 
 perament dictates. 
 
 It is a rare day for the aerial traveler to see 
 the shifting of the scenery of cloudland. Flying 
 on clear days is dull compared with those marvel- 
 ous days when broken clouds are ever-changing 
 "in form and color. Cross-country flights on clear 
 days are delightful owing to the changing pano- 
 ramas but even on such days, a way-side flock of 
 clouds is welcomed for the variety it introduces. 
 However, on those fitful days when many types 
 of clouds are present at various altitudes, the de- 
 lights of an hour in cloudland are immeasurable. 
 On such a day the aerial traveler is greeted with 
 a new setting every moment. 
 
 Heading into the strong breeze which is but a 
 reminder of the battling winds above, two airmen 
 take to the air. Their course is directly toward 
 the scowling nimbus to the west which is shower- 
 ing the earth beneath. The day is chilly and not 
 conducive to the formation of towering cumulo- 
 
78 THE BOOK OF THE SKY 
 
 nimbus or thunderclouds which, might lash the 
 earth with rain and hail. Little danger lurks in 
 the heights above, despite the uncertain aspect of 
 the sky. Eising higher and higher, they note the 
 brighter spaces beyond the frowning nimbus 
 which means that the shower to the west is merely 
 a local one. Circling back in their climb they 
 approach the lower level of the cloud from which 
 a fitful rain is falling a few miles to the west. 
 Already they have passed through the scudding 
 fragments torn from the rain cloud. As they con- 
 tinue to climb, they soon approach the region of 
 the torn fragments of cumulus clouds which are 
 speeding eastward in a gale. These clouds are 
 rolling or tumbling as the upper portions are 
 driven ahead of their bases which are retarded 
 by the slower winds of the lower altitude. 
 
 Banking stiffly, the airmen head their craft 
 again to the westward to fight the strong westerly, 
 wind. They are now at an altitude of about a 
 mile and are entering the region of the tattered 
 cumuli. Up and up they climb and attempt to 
 steer their way between these clouds. How won- 
 derful are these intimate associations 1 The woolly 
 clouds with wind-blown edges are all around them 
 like icebergs -in a dark sea. Some are warmly 
 bright in the sunshine; others are coldly dark in 
 the shadows cast by the clouds above. But all of 
 them hold the same straining attitude as if they 
 were racing each other. They lean forward as if 
 urging onward by sheer will-power their lagging 
 
MINGLED MOODS 79 
 
 extremities. Despite their attempts to steer clear 
 of these vaporous bergs, occasionally as the air- 
 men circle back in the constant battle with the 
 strong west wind, they collide with one of them. 
 The collision is noiseless and nnfelt, but for a few 
 moments they are blinded as they pass through 
 this lump of fog. The air is "bumpy," for the 
 eddies and battling currents made visible by the 
 clouds buffet the aircraft gently. 
 
 As the airmen reach an altitude beyond the 
 crests of these straining racing clouds, they enter 
 an open space, but far above them, floating upon 
 the blue sea, are the beautiful symmetrical pat- 
 terns of the billowed clouds. This high stratum 
 appears nearly stationary, but this is because of 
 its height or distance. Even still higher, streaks 
 of cirrus clouds are visible between the billows. 
 Toward the west appears the rounded top of the 
 cumulo-nimbus poking its crest above the level 
 of the fleeting cumulus clouds. Bathed in sun- 
 light with the small shadows of the upper clouds 
 flitting over its brilliant vaporous head, it is a 
 beautiful sight. It is difficult to visualize this 
 snow-white crest as a part of that dark cloud 
 which the airmen saw a few minutes ago frown- 
 ing and shedding rain upon the earth. ,Here in 
 the varying light it is as snow-white as the clouds 
 surrounding it. By contrast with these upper 
 surfaces, the high clouds are now gray although 
 from the earth they appeared bright, cheerful, 
 sunlit bits among the darker clouds of the lower 
 
80 THE BOOK OF THE SKY 
 
 levels. Far and wide beyond this rearing cumulo- 
 nimbus, the small fracto-cumuli lie scattered like 
 patches of ice floating in a dark greenish sea. 
 Their brilliant white surfaces, through contrast, 
 make the earth appear dark and foreboding and 
 they have been flattened by distance, for the air- 
 men have mounted far above their level. 
 
 As they reach an altitude of 10,000 feet they 
 clear the top of the cumulo-nimbus from which 
 rain is falling. Far above them, perhaps at an 
 altitude of 15,000 or 20,000 feet is the sheet of 
 billowed cloud which so picturesquely makes vis- 
 ible the intricate currents of the air. The air- 
 men note by the drift of their craft that they are 
 now in a cross-current of air. A few stray bits 
 of fog-like clouds float just above their level, sur- 
 vivors, perhaps, of alto-cumuli or rearing cumuli 
 which may have passed along recently or which 
 may have partially evaporated on meeting the 
 thirsty air of a cross-current. The space immedi- 
 ately surrounding them appears to offer no more 
 clouds to visit. The billowed layer above, which 
 trails off toward the horizon in fore-shortening 
 waves and ends in an apparently even layer, is 
 too far above them to consider at present. How- 
 ever, there lies to the northward at an elevation 
 somewhat above them, a thia flat cloud which 
 appears interesting. 
 
 They head their craft toward this and are borne 
 rapidly toward it in the strong wind. As they 
 approach it they note a white film-like veil pen- 
 
MINGLED MOODS 81 
 
 dent beneath it and this shines brightly in the sun- 
 light. As they gain an elevation somewhat above 
 it they note that its upper surface is slightly ir- 
 regular and beautifully white. The thin white 
 veil draping from its lower surface extends down- 
 ward for about 2000 feet and from its unpat- 
 terned textureless character they conclude that 
 it is rain falling from the flat cloud. A glance at 
 the thermometer contradicts them because it is 
 registering several degrees below freezing. Then 
 it must be snowing! Here in the summertime, at 
 an elevation of slightly more than two miles, a 
 snowstorm is taking place in the aerial world, 
 unnoticed and unfelt by mankind below. They 
 dip downward toward this pendent veU and 
 shortly they enter it. For a few damp moments 
 they are blinded, but they soon emerge in the clear 
 sunlit atmosphere below. They have passed 
 through falling snow and then rain in these few 
 moments, but where does the snow fall? It falls 
 about 2000 feet from its source in the flat sheet 
 above and is then devoured by the cross-current 
 of relatively dry air which it meets. How often 
 such aerial events take place without being heeded 
 by mankind on earth! From high clouds fihny 
 tufts sometimes appear to be hanging like white 
 whiskers. These may actually be falling rain or 
 snow which is evaporated as it meets a stratum 
 of air whose relative humidity is low. 
 
 Many other interesting events lie within the 
 range of the airmen on this fitful day but they 
 
82 THE BOOK OF THE SKY 
 
 are out for only an hour or two. Tlie billowy 
 layer above tbem is too high for tbis trip. As 
 they gaze upward for a parting glance before they 
 descend they note that it has changed. The bil- 
 lows are now almost invisible. Over a portion of 
 the sky they have apparently evaporated, expos- 
 ing the higher filmy cirrus clouds clearly to view. 
 Over the remaining portion they appear to have 
 coalesced into a thicker mass which is seared with 
 bold stream-lines of light and shade, appearing 
 as if this thickened mass were drawn out by a 
 powerful wind. Thus the conflicting winds, vary- 
 ing in their appetites for water-vapor, mould or 
 devour the clouds as they please. 
 
 The airmen dip the craft downward at a gentle 
 glide and steer toward the rounded cumulo-nim- 
 bus which marks approximately their field. The 
 same pattern of tattered cumuli lies below them. 
 From this high altitude they appear flattened, 
 hence they lie like ice-cakes on a dark sea. From 
 a lower altitude they assume a third dimension 
 and appear more like white bergs. Vertically 
 below them these fragments are scattered, but far 
 toward the horizon whence they came, they ap- 
 pear en masse. In the distance toward which 
 these clouds are traveling they also appear packed 
 as if there lies the rendezvous of the assembling 
 cohorts. 
 
 As the airmen approach the rearing crest of the 
 cumulo-nimbus it is seen to be much changed in 
 appearance. Instead of the compact rounded 
 
MINGLED MOODS 83 
 
 crest, many crevices appear. The huge cloud- 
 mass is disintegrating after having performed its 
 office. At its crest a white banner develops and 
 begins to strain in the wind. The high wind at 
 this level is tearing a piece from the crest of this 
 thnnderhead. As this fluttering straining banner 
 elongates it seems to be drawn more and more 
 rapidly until soon it becomes detached. It drifts 
 rapidly away from its parent, an isolated tattered 
 fragment launched by the wind upon a brief 
 career. It may travel far before it vanishes or 
 , loses its identity by merging into a mass of cloud, 
 but likely it is destined soon to be drunk by 
 a thirsty wind. Perhaps at best, it will evaporate 
 with the approach of night, disappearing like a 
 spirit into that invisible aerial world whence it 
 came. 
 
 The large crevices in the thnnderhead widen 
 and deepen and soon large masses are separating 
 as if to wander again at play with the winds after 
 having faithfully gathered to bestow the blessing 
 of rain upon the earth. The day is waning and 
 with it the strength of the vertical convection cur- 
 rents diminishes. The cloud in performing its 
 duty also has suffered internal modification. No 
 longer reinforced by the upward currents, and 
 having performed its office, this huge assemblage 
 is adjourning. Its disintegration into masses of 
 various shapes and sizes is one of the worthy 
 spectacles of cloudland. 
 
 The oblique rays of the sun dimly illuminate 
 
84 THE BOOK OF THE SKY 
 
 tlie liaze and mist in the depths of these clouds 
 and the blue light from the sky combining with 
 this light gives a purplish tinge to these depths. 
 The side of the cloud in full shadow is a bluish 
 shade and the sunlit crests are white. The color 
 contrasts, the variety of pattern, and the modula- 
 tions of light and shade in the oblique sunlight 
 combine to give these clouds a high place among 
 the sculptures of cloudland. 
 
 All these things and many more the observing 
 airmen saw in an hour or so on this day of many 
 moods. Through the combination of observation 
 and knowledge, the aerial world becomes a place 
 of ever-widening interest. As they glide down- 
 ward and come to a safe landing it is difficult for 
 them to believe that they left the earth such a 
 short time ago, for in that brief sojourn aloft, the 
 weather conditions of a cycle of seasons were 
 experienced. Besides these, the beauties, won- 
 ders, and interesting phenomena of another world 
 greeted them every moment. As they walk home- 
 ward they glance at the opalescent sky and wonder 
 if they will ever exhaust this source which so far 
 has been one of intense and perpetual interest. 
 
CHAPTER IX 
 
 SUNSET COLOES 
 
 "Die down, dismal day! 
 And come, blue deeps! magnificently strewn 
 With colored clouds — large, light, and fugitive — 
 By upper winds through pompous motions blown." 
 
 — David Gray. 
 
 DISMAL indeed is the glorious day com- 
 pared with the radiant splendor of the 
 setting sun. Is it mere fancy that the thick veil 
 which hangs in the sky all day long thins or parts 
 for this nightly benediction? Is it mere fancy that 
 a sky which has remained serene and cloudless all 
 day long is visited in the west by at least a few 
 clouds to add something to this au revoirf Sel- 
 dom is the observer disappointed who looks 
 toward the west at the appointed hour, for here 
 in its variety of color, pattern, and mood is the 
 silent benediction. Doubtless there is always a 
 tinge of sadness to this splendid scene but 
 scarcely sorrow. Herein lies the difference be- 
 tween certainty and uncertainty. The death-bed 
 of life is shrouded in deepest sorrow but that of 
 
 85 
 
86 THE BOOK OF THE SKY 
 
 the day is beautiful. The sun will rise again on 
 the morrow — ^that is certain. 
 
 Of those millions who gaze at the sunrise and 
 sunset and note its complexity of color, changing 
 from moment to moment, are there many who 
 know that the cause is simple? It does not add 
 to the beauty of the display to know the reasons, 
 but it adds an interesting phase to the pleasure 
 of observing and of studying the phenomena of 
 the sky. To the aerial traveler who soars upward 
 from one cloud level to another, as the sun is set- 
 ting, the scheme of coloring is simple. At an ele- 
 vation from which he is able to look down upon 
 some layers, along the level of another, and up 
 at the remaining layers, the whole scheme of the 
 painting of the sunset is laid bare. The arrange- 
 ment of colors on Nature's palette is very ele- 
 mentary. 
 
 AVhen the sun is high in the heavens there are 
 two chief sources of the colors which the clouds 
 display, namely, the sun and the sky, but super- 
 imposed upon everything is the bluish color of 
 the earth-haze. When looking vertically upward 
 from the earth or vertically downward from an 
 aircraft at high altitudes, the observer looks 
 through about a mile depth of haze ordinarily. 
 However, this depth rapidly increases with the 
 obliquity of vision ; hence, the color of objects im- 
 mersed in or beyond the haze will depend par- 
 tially upon its color and this color deepens with 
 the depth of the haze. The clear sky, of course, 
 
SUNSET COLORS 87 
 
 is a deep blue outside the earth's haze and noon 
 sunlight may be considered to be white. However, 
 by contrast with the blue sky, the sun or sunlit 
 white clouds appear yellowish. The effect of this 
 contrast may be eliminated by looking at a sunlit 
 cloud through a hole in a black cardboard held 
 at an arm's length. The effectiveness of this con- 
 trast in making the white sunlit clouds appear 
 of a yellowish tint is obvious to the observant 
 aerial traveler. The same sunlit clouds which 
 against the sky appear yellowish appear white 
 when viewed from above against the dark duU 
 tertiary earth-colors. 
 
 The portions of clouds in shadow will receive 
 skylight predominantly, hence the bluish appear- 
 ance of these shadows. The thinner the clouds 
 are, the lighter the shadows. In these cases some 
 diffused sunlight reaches the shadow through the 
 cloud and is mixed with the blue skylight. Dense 
 haze often appears to assume a purplish tinge. 
 The effect of the haze can best be understood and 
 visualized if it is studied first by the example of 
 cigar smoke, for the earth-haze consists chiefly 
 of dust and smoke carried upward largely by the 
 diurnal convection currents. Furthermore, smoke 
 consists of carbon particles and is similar to dust. 
 
 If one stands in the sun near a white surface 
 and observes the shadow of a dense cloud of 
 smoke cast on a white surface, it wiU be noted 
 that the smoke alters the sunlight in a manner 
 Bimilar to a brownish glass. At this point it is 
 
88 THE BOOK OF THE SKY 
 
 well to recall that stmliglit contains light rays of 
 many colors whose combined action upon the 
 visual organ produces the sensation of white, but 
 if the quantitative relation of these colored com- 
 ponents is changed, the combined color is in gen- 
 eral altered. The principal components are seen 
 in the rainbow; by means of the refractive prop- 
 erty of the raindrops the heterogeneous sunlight 
 has been separated into its components, which are 
 chiefly violet, blue, green, yellow, orange, and 
 red. A red glass transmits the red rays prin- 
 cipally, hence through it a white object appears 
 red. A white object will also appear red if it is 
 illuminated by red light. The first case is in 
 reality the same as the second because the other 
 colored components in the light in the first case 
 are ineffective owing to the fact that the red glass 
 does not permit them to reach the eye. 
 
 It follows from the foregoing that the cloud of 
 smoke casts a reddish or brownish shadow be- 
 cause it partially obstructs the blue and violet 
 rays. This obstruction is caused partially by 
 actual absorption and partially by scattering the 
 violet and blue rays more than the other compo- 
 nents. If the cloud of smoke be observed closely 
 it will be seen to have a bluish tinge in the sun- 
 light, this bluish tint being approximately com- 
 plementary to the brownish shadow. If a quan- 
 tity of smoke be drawn into the mouth from the 
 cigar and retained there for a minute or two and 
 then puffed out into a cloud, it will be seen not 
 
SUNSET COLORS 89 
 
 to cast a sliadow as pronounced in color as that 
 in the first case. Furthermore, the cloud of 
 smoke will now appear white in the sunlight in- 
 stead of bluish. While these minute particles of 
 smoke were retained in the moist cavity of the 
 mouth, moisture gathered upon them, for mois- 
 ture desires small nuclei upon which to condense. 
 This made the individual particles of the cloud 
 much larger in the second case. Now what dif- 
 ference does the size of particles of dust or smoke 
 make? In fact, size appears to make nearly all 
 the difference. Very minute particles scatter the 
 violet, blue, and green rays (technically stated as 
 those rays of shorter wavelengths) more than the 
 yellow, orange, and red rays (those of longer 
 wavelengths). For example, the blue sky owes 
 its color chiefly to this partiality and if there were 
 no particles of dust, smoke, gas molecules, etc., 
 in the sky to be illuminated by the light which is 
 scattered by them and also by sunlight, the sky 
 would be hlach in daytime. At high altitudes the 
 sky does become very dark blue, apparently due 
 to this selective scattering of sunlight by the pure 
 dust-free atmosphere of the upper regions. 
 
 Another important phase is the effect of thick- 
 ness in altering the color. The sun viewed 
 through an amber liquid will appear orange if 
 the depth of the liquid is increased sufficiently, 
 and finally will appear red through a great depth. 
 In a similar manner, the earth's haze alters the 
 suillight more and more as the density or depth 
 
90 THE BOOK OF THE SKY 
 
 of the haze increases. This progression of color 
 varies somewhat from time to time but usually is 
 yellow, orange, red. Adding to these colors the 
 color of the bluish and purplish haze, such colors 
 as rose, purple, and salmon pink are produced. 
 The chief details in the production of sunset 
 colors are thus explained, however, a thorough 
 discussion would occupy several chapters. These 
 simple and hurried explanations should help the 
 reader to account for all the sunset colors. 
 
 It should not dull the beauty of sunsets to know 
 that the colors are born in the smudge of the 
 earth-haze. In fact, this should exalt the atmos- 
 pheric haze, for without it the sky would vary 
 little in color from that at noonday. In fact, even 
 the delicate pastel shades of the clouds low down 
 in the sky at noon would disappear and the clouds 
 would appear as boldly against the deep blue as 
 those in the zenith. Without this foreign matter 
 in the atmosphere, twilight would be brief and the 
 glorious afterglow which is sometimes seen for 
 an hour or two after sunset would never appear. 
 This earth-haze which looks like smudge and 
 filthy air from high altitudes extends ordinarily 
 to an elevation of about a mile; sometimes as 
 high as two mUes ; and on rare occasions into the 
 cirrus-cloud region. Besides this "dust" haze, 
 there appears to be a faint haze of another va- 
 riety which contributes to the sky brightness but 
 perhaps not much toward the production of sun- 
 
SUNSET COLORS 91 
 
 set colors. A discussion of tMs unimportant haze 
 is too complicated for presentation here. 
 
 When the sun is setting blood-red at the earth's 
 surface the aerial observer at an altitude of two 
 or three miles sees the color scheme spread out 
 before him. The lowest clouds are tinged with 
 red, the next higher are of an orange tint; those 
 at his level are a brilliant yellow ; and the fibrous 
 cirri two or three miles above him are still bathed 
 in the yellowish white sunlight. Before the direct 
 sunlight reaches the clouds at low altitudes it must 
 pass through great depths of the densest haze. 
 In reaching the higher clouds, the depth of the 
 path of the sun's rays through the haze is consid- 
 erably less than in the preceding case, further- 
 more, the density of the haze diminishes some- 
 what with altitude. From his position three miles 
 above the earth the observer sees the sun prac- 
 tically free from haze and if he were among the 
 cirrus clouds, scarcely any dust haze would be be- 
 tween him and the sun. 
 
 From his position the sun is not yet setting, 
 though viewed from the earth it is already touch- 
 ing the horizon. As he watches from his aerial 
 lookout he notes the sun gradually becoming 
 redder as it approaches the horizon which he can 
 barely distinguish owing to the depth of the haze. 
 The lowest clouds gradually lose their reddish 
 tint and as their crests are barely tipped with red 
 their bases are already in deep purplish shadow. 
 The blood-red is now replacing the orange of the 
 
92 THE BOOK OF THE SKY 
 
 clouds next above the lowest and the orange has 
 moved up to replace the yellow of those at the 
 airman's level. The high cirri are now beginning 
 to assume a stronger tinge of yellow. This suc- 
 cession of color is moving upward as the moments 
 pass. 
 
 The earth is now in deep shadow and the low 
 clouds have lost their warmth of color. They are 
 now faintly illuminated with the colder colors of 
 the sky. For the observer at the earth's surface, 
 the sun has set some time ago, and the sky shows 
 a succession of delicate tints from red at the 
 horizon through orange, yellow, and green to blue 
 at the zenith. The aerial observer also sees these 
 but they are more delicate tints to him. 
 
 As the moments pass, the observer sees the red 
 sun touch the horizon and the clouds about him 
 are immersed in a flood of red light. Those below 
 him are all in shadow and the fibrous cirrus far 
 above are assuming a salmon pink color. They 
 are bathed in orange light but the blue of the sky 
 showing through their thin fihny bodies mixes 
 with the orange and gives it a pinkish tinge. The 
 watcher down on earth is now in twilight; the 
 sun's glow in the west is rapidly dying; the 
 zenith sky is now "fretted with gold" — the work 
 of the cirrus clouds. 
 
 For the watcher above, the sun has now set. 
 All the world below him is in cold deep shadow. 
 Some of the clouds just below him are still bathed 
 in reflected glory and the upper clouds are now 
 
SUNSET COLORS 93 
 
 assuming the red tints of the snn which is near- 
 ing the horizon. The airman drops from his 
 bright zone toward the deep shadows of earth. 
 Only a few minutes elapse before he straightens 
 out to approach the earth cautiously, for lo ! it is 
 almost dark down there. CarefuUy maneuvering 
 in the dim twilight, several minutes elapse and, 
 when finally he lands, the night lights burst forth. 
 Truly the aerial world so near is yet so far. In 
 a few minutes he comes from the splendor of sun- 
 set at polar temperature (nearly zero Fahren- 
 heit) to the suffused darkness of a summer's 
 evening. 
 
 The aerial observer of the sunset seeks the cool- 
 ness of the lookout by the lake, for the hot humid 
 summer atmosphere is stifling after his hour aloft 
 in the arctics. The earthly observer of the sun- 
 set is in the lookout where he also watched the 
 sun quench its fires beneath the watery horizon. 
 They compare notes of colors and clouds even to 
 the details of the cloud-forms. The variation in 
 the observations from the two viewpoints is in- 
 teresting and instructive. An hour elapses dur- 
 ing which they have lived over the details of the 
 sunset. It is now dark but a faint pinkish glow 
 is diffused from the zenith. The twilight limit 
 about fifty or a hundred miles above them is still 
 bathed in the sun's radiance. That ethereal some- 
 thing which exists so vanishingly thin in the rare- 
 fied atmosphere of the twilight region far above 
 the shallow stratum invaded by mankind, glows 
 
94 THE BOOK OP THE SKY 
 
 faintly in the darkness. On rare occasions this 
 afterglow is fairly intense, bespeaking variations 
 in the meteorological conditions of this frigid re- 
 gion where the atmospheric density has decreased 
 to almost nothing, marking the approach to that 
 absolute zero of dead space in which other insig- 
 nificant planets and solar systems exist millions 
 and billions of miles apart. In this infinity of inter- 
 stellar space worlds are being born and worlds 
 are dying each in its orderly manner ordained by 
 Nature. Occasionally the cosmic dust is disturbed 
 for the briefest moment by the erratic meteoric 
 traveler who has broken the bonds of patient 
 methodic order only to suffer total destruction 
 for his rebellious spirit. A brilliant trailing flash 
 as he enters the earth's atmosphere and he van- 
 ishes in the fires of friction, his ashes to mingle 
 eternally with the cosmic dust. Or will they, eons 
 hence, be drawn into a nebulous womb, eventually 
 to be born a part of another star therein to be 
 imprisoned forever and ever? 
 
CHAPTER X 
 
 AFTERGLOW 
 
 "0, TmlighL' Spirit that does render iirth 
 To dim enchantments, melting heaven with earth." 
 
 — (Mrs.) Norton. 
 
 TWILIGHT may have been meant by tbe Cre- 
 ator for a period of grace to safeguard His 
 primitive beings from the hazards attending the 
 sudden arrival of darkness. This modulation of 
 day into night may serve many utilitarian pur- 
 poses, but its beauty and mood impress the intel- 
 lect and the imagination of those attuned to 
 respond. The quietly fading splendor of the sun- 
 set is a benediction at the close of day. Its mood 
 is restful and prepares one for the period of rest 
 to follow. Herein it holds an advantage over 
 sunrise for mankind at dawn has the day's work 
 before him. His mood is not such as to permit 
 him to quietly contemplate the beauties of the 
 dawn and sunrise, for his day's work beckons. 
 However, sunrise, symbolic of the beginning, does 
 fill an office opposed to that of sunset. But both 
 dawn and twilight have their variety. In the open 
 places near the heart of Nature the last lingering 
 
 95 
 
96 THE BOOK OF THE SKY 
 
 flush of the sky fades to the accompaniment of the 
 music of night-sounds in summer. As twilight 
 fades over the metropolis, civilization's lights 
 twinkle in increasing numbers through the hazy 
 veil. The mood varies with the outlook of the 
 individual, with the season, and with the locality. 
 The duration of twilight is ordinarily subject 
 to minor variations occasioned by the variable 
 amount of haze and clouds in the atmosphere and 
 by their distribution which depends upon the 
 winds, convection currents, and preceding weather 
 conditions. For these reasons the morning twi- 
 light or dawn is generally of shorter duration i 
 than evening twilight even at the same place and 
 on the same day. The duration of twilight has 
 been found ordinarily to extend throughout the 
 period of time required by the sun to traverse an 
 arc of about eighteen degrees of vertical depres- 
 sion. During an equinox when the sun is de- 
 pressed vertically below the earth's horizon, the 
 duration of twilight is ordinarily seventy-two 
 minutes. In those latitudes where, for certain 
 periods of the year, the sun is not depressed as 
 much as eighteen degrees vertically below the 
 horizon throughout the night, darkness is not 
 complete for those periods. Inasmuch as the 
 plane of the sun's apparent path varies in ob- 
 liquity to the earth's horizon with the latitude, 
 different periods of time elapse for an eighteen- 
 degree vertical depression, hence the duration of 
 twilight varies with latitude. 
 
AFTERGLOW 97 
 
 The sky is often remarkably clear and deep blue 
 after a period of cloudy and rainy weather. The 
 lower atmosphere has been washed, as it were, and 
 the conditions have not been conducive to the 
 maintenance of the haze in the lower atmosphere 
 commonly replenished by the dust and smoke 
 carried upward by the diurnal convection cur- 
 rents. Extensive forest fires, volcanic eruptions, 
 and long periods of dry hot weather when the 
 atmosphere is relatively quiescent for miles 
 above, have been responsible for some of the 
 extraordinary afterglows. Perhaps another con- 
 dition necessary for the carriage of haze to great 
 heights is a continuous decrease of temperature 
 with altitude, — ^that is, the existence of no tem- 
 perature inversions or strata of air warmer than 
 those below them. 
 
 Two airmen sit watching the brilliant splendor 
 in the trail of a sunset. The whole sky is aglow 
 with a shimmering rosy light. Their conversa- 
 tion turns toward the glowing heights, for they 
 know that the sun still shines up there. They 
 have sported in the splendor of the setting sun 
 amid the fairyland above them when the earth 
 below was already in deep shadow. These 
 thoughts bring to mind the ever-expanding won- 
 ders of flying. The airplane has telescoped dis- 
 tance; it has brought the polar climes of the 
 heights above within an hour's ride; it has 
 brought cloudland almost to man's very door; in 
 fact, it has opened to mankind the beauties, the 
 
98 THE BOOK OF THE SKY 
 
 wonders, the mysteries of the aerial world above. 
 
 "With attention turned to the glowing zenith, the 
 airmen realize that from a position two or three 
 miles above they would be watching the sunset. 
 But they have just witnessed the glory of a sun- 
 set. Could it be that they might witness two 
 successive sunsets on the same evening? If pos- 
 sible, surely that would be doubling the joy of an 
 evening and would be adding another -triumph to 
 the records of flying. 
 
 Assuming the conditions of the equinox and a 
 position at the equator, at this time and place 
 the sun's depression below the horizon is perpen- 
 dicular and, consequently, the duration of twilight 
 is the briefest possible for a given atmospheric 
 condition. At times other than at an equinox the 
 twilight period is of longer duration owing to the 
 fact that the earth's axis is inclined and therefore 
 a longer time elapses per degree of vertical de- 
 pression of the sun. Simple computations indi- 
 cate that, under the conditions assimaed above, in 
 an aircraft climbing at the rate of about 1000 feet 
 per minute vertically, for the first mile of altitude 
 one is able to see two sunsets in the evening. For 
 example, if one started aloft just as the sun 
 touched the horizon and climbed in such a manner 
 that his resultant vertical velocity was 1000 feet 
 per minute, the sun would begin apparently to 
 rise at first and then gradually to set again. 
 When an elevation of about 5000 feet was reached 
 at this constant resultant vertical velocity, the 
 
AFTERGLOW 99 
 
 sun would appear to be just toucMng the horizon 
 again. Powerful aircraft are able to do this. 
 In order to make the sun appear stationary at the 
 horizon (at the equator during an equinox) one 
 must reach altitudes of one mile in slightly over 
 five minutes ; two miles in slightly over seven min- 
 utes ; three miles in about nine minutes ; four miles 
 in somewhat more than ten minutes. In about 
 thirty-six minutes the sun will just be setting for 
 a position at fifty miles above the earth's surface. 
 Considering the latitudes of the United States at 
 other times than an equinox an aircraft would not 
 need to climb as fast as one thousand feet per mia- 
 ute for the first five minutes to see two very dis- 
 tinct sunsets with a sunrise between them on the 
 same evening. 
 
 These considerations turn the attention of the 
 airmen to a further discussion of the afterglow 
 and one of them describes an extraordinary mid- 
 summer afterglow and the conditions attending it. 
 The place of observation was in eastern Iowa. 
 For eight successive days not a cloud appeared in 
 the sky and little or no dew was deposited at 
 night. The temperature during the day hovered 
 near 100° Fahrenheit but the air was relatively 
 dry. One had the feeling that there were no ap- 
 preciable winds for miles above. These, appear to 
 be ideal conditions for the dust of the parched 
 earth and the smoke of civilization and perhaps 
 of some forest fires, to be carried upward and 
 upward by convection currents which are not 
 
100 THE BOOK OF THE SKY 
 
 interrupted as ordinarily at altitudes of a 
 mile or two. At any rate, the brilliance of the 
 sun was very much subdued all day long and 
 appeared pinkish, a brilliant salmon pink after- 
 glow lingering perhaps two or three hours after 
 the sun had set. Various indications pointed to 
 the extension of this glowing haze to many miles 
 vertically upward. About an hour after sunset 
 this glow was extremely brilliant and began to be 
 seamed with straight radial shadows pointing 
 toward the sun already far below the horizon, as 
 though distant clouds beyond the horizon were in- 
 tercepting the sunlight and casting shadows across 
 the afterglow. But clouds had not been seen dur- 
 ing day or night for several days, up to this time, 
 and eventually not for eight days; furthermore, 
 these shadows appeared to be quite similar 
 nightly. The first fact pointed to the unlikelihood 
 of the existence of clouds; the second, if the 
 shadows were really alike each evening, pointed to 
 the necessity of the same forms each evening for 
 casting the shadows. These shadows faded out 
 gradually with the afterglow although the latter 
 lingered when it was too faint to distinguish the 
 former if they were still present. 
 
 Clouds could account for these radial shadows 
 which seamed the afterglow but the complete ab- 
 sence of clouds for eight days, during which this 
 phenomenon was noticed the last five evenings, im- 
 pelled one to seek another solution. What else 
 could cause these shadows in that rolling prairie 
 
AFTERGLOW 101 
 
 wMeh extended uninterrupted to the westward for 
 hundreds of miles? Could these shadows be cast 
 by the Eocky Mountains about eight hundred 
 miles to the westward? This was a daring thought 
 which grew more and more fascinating. The 
 eclipse — a shadow cast sometimes millions of 
 miles through space — ^is not startling because 
 magnitude is a characteristic of interstellar space. 
 But to witness or even to think of shadows cast by 
 the jagged crests of a range of mountains nearly 
 a thousand miles away on the earth is fascinating. 
 At least it appeared worthy of the application of 
 computations. 
 
 Assuming crests of the mountain range to be at 
 an elevation of about 2^^ miles above the elevation 
 of the plain eight hundred miles to the eastward, 
 the problem became one of ascertaining how far 
 above the latter locality the shadows would fall if 
 they were just tangent to the proper point of the 
 earth's surface somewhere to the west. In other 
 words, if one stood at this point of tangency and 
 saw the sun just setting over the mountain range 
 to the west and then turned his gaze to the east- 
 ward and followed this line extended to the east- 
 ward, how far above the given spot in Iowa would 
 this line pass? Computations indicated that this 
 would be slightly more than 60 miles above the 
 earth's surface. Apparently this is within the 
 twOight limit and, inasmuch as the radial shadows 
 were visible at least an hour and quite certainly 
 longer, there is a possibility that on these ocea- 
 
102 THE BOOK OF THE SKY 
 
 sions of exiraordinary afterglow there was wit- 
 nessed the shadows cast by the Eocky Mountains 
 eight hundred miles to the west. It is possible 
 that clouds far below the horizon were responsible 
 for the shadows, but under the conditions the other 
 cause is plausible. 
 
 Thus the sky which is empty to most persons is 
 full of interest to the observer. Besides furnish- 
 ing a vast variety of beauty, of moods, of wonders, 
 and of mysteries, there is something about its 
 contemplation which kindles the imagination. 
 Those who by habit are observing and by the 
 kindness of fate possess sensibilities which feel 
 the mood and charm of Nature are fortunate in- 
 deed if their course has led them into the aerial 
 kingdom. How intimate the sky becomes to them ! 
 How much greater their world grows ! And where 
 their material wings cannot carry them, they go 
 thither on the swift, tireless wings of imagination. 
 
 The airmen watch the afterglow fade and grow 
 faint. Knowing the limitations imposed by the 
 rapidly decreasing density of the atmosphere with 
 altitude, they dare not hope ever to visit that twi- 
 light limit up above. But as the last flush of the 
 afterglow disappears and they stroll homeward, 
 they satiate that longing with a promise to see two 
 sunsets tomorrow evening. 
 
CHAPTER XI 
 
 A POLAR CLIMB 
 
 "27ie chasm of shy above my head 
 Is Heaven's profoundest azure. No domain 
 For fickle, short-lived clouds, to occupy. 
 Or to pass through; — hut rather an abyss 
 In which the everlasting stars abide. 
 And where soft gloom, and boundless depth, might tempt 
 The curious eye to look for them by day." 
 
 — WOKDSWOBTH. 
 
 IT is a calm, cloudless day in late summer and 
 tlie sky is of that deep clear trembling blue 
 which sometimes follows a rainy spell. It is one 
 of those rare days for exploring the upper regions 
 and two airmen succumb to the call of the blue 
 heights. They have often discussed a climb to the 
 ceiling — ^the highest altitude attainable by their 
 craft — and this is the ideal day for such a flight. 
 This will not be an altitude record, but they will 
 ascend to the ceiling for their craft, which wUl be 
 more than four miles above them. They examine 
 the oxygen tanks and helmets, for in that rarefied 
 atmosphere above they must supply their own 
 oxygen if they would not run the risks of going to 
 
 103 
 
104 THE BOOK OF THE SKY 
 
 sleep for lack of sufficient oxygen. They don their 
 arctic clothes, for they are going where the tem- 
 perature will be below zero Fahrenheit. Their 
 preparations are based upon experience and upon 
 a knowledge of many general facts of the atmos- 
 phere. 
 
 The atmosphere at the earth's surface consists 
 principally of nitrogen and oxygen, the former 
 comprising about 78 per cent of a given volume 
 and the latter about 21 per cent. The remaining 
 one per cent is made up chiefly of argon, carbon 
 dioxide, hydrogen, neon, and heliinn, ranking in 
 volinnetric proportion in the order given. Owing 
 to the continual stirring of the atmosphere by con- 
 vection currents, the volumetric proportions of 
 the different gases are practically the same up to 
 about seven miles. Above this altitude the tem- 
 perature changes only slightly with elevation and, 
 therefore, vertical convection is absent. In this 
 region the gases are distributed according to their 
 relative weights. 
 
 The content of water-vapor in the lower atmos- 
 phere varies considerably, but decreases with alti- 
 tude, so that the absolute humidity is practically 
 zero at altitudes above seven miles. 
 
 The temperature decreases rapidly with eleva- 
 tion but varies for different places and seasons. 
 There is less difference between the summer and 
 winter temperatures of high altitudes than of low 
 ones, and as would be surmised, at very high alti- 
 tudes the temperature is not affected by the sea- 
 
A POLAR CLIMB 105 
 
 sonal cHanges at the earth's surface. In fact, 
 above seven miles in the latitudes of the United 
 States, the temperature changes very slightly with 
 elevation in the region which has been explored by 
 means of small balloons equipped with instru- 
 ments. This region is called the "stratosphere" 
 and its temperature averages about 65° Fahren- 
 heit below zero. The altitude of the lower surface 
 of the stratosphere at the equator is nearly ten 
 miles and its average temperature is about 95° 
 below zero. The temperatures of the lower levels 
 vary considerably but in the summertime in the 
 temperate zones freezing temperatures are com- 
 monly encountered at two miles or slightly above, 
 and zero Fahrenheit is encountered at elevations 
 of about four miles. Although the rate of de- 
 crease of temperature with altitude varies consid- 
 erably with elevation, season, and locality, a very 
 rough approximation is a decrease of about 4° 
 Fahrenheit for each 1000 feet above the first half 
 mile. "When the temperature at the earth's sur- 
 face is high, the rate of decrease of temperature 
 with altitude is usually higher for the first mile or 
 two than when the surface temperature is low. 
 
 The atmospheric pressure decreases with alti- 
 tude as is well known by experiences on earth. At 
 an altitude of three miles the pressure is about 
 one-half the value at sea-level ; at seven miles it is 
 about one-fourth; and at twenty miles it has de- 
 creased to about one-hundredth the value at sea- 
 level. 
 
106 THE BOOK OF THE SKY 
 
 The winds which play such a part in whipping 
 the clouds into various shapes and patterns, thus 
 revealing themselves, increase in general with 
 altitude, although their velocities in the cloud 
 region vary greatly from day to day. In the north 
 temperate zone the winds in the upper cloud 
 region are more rapid in winter than in summer, 
 but in the intermediate and lower cloud regions 
 they apparently are in general somewhat slower 
 in winter than in summer. Approximate average 
 velocities of winds at Washington, D. C, for 
 various altitudes are : 25 miles per hour at an ele- 
 vation of one mile ; 35 miles per hour at two miles ; 
 40 miles per hour at three miles; 55 miles per 
 hour at five miles ; 65 miles per hour at six miles. 
 In this country the maximum velocities of west- 
 erly winds in the upper cloud region attain over 
 200 miles per hour and a velocity of 175 miles per 
 hour is not rare. The eastward movements of 
 storm-centers or cyclonic areas in the north tem- 
 perate zone are generally at the rate of twenty to 
 thirty miles per hour and in the direction of the 
 higher clouds or of the atmosphere at altitudes of 
 four to six miles. 
 
 These are some of the more important aspects 
 of atmospheric conditions with which the weU- 
 equipped airman is familiar. Meteorology will 
 become a science of more general interest as man- 
 kind becomes absorbed in flying, and in return for 
 the aid that meteorology has given to aviation in 
 
A POLAR CLIMB 107 
 
 its infancy, aviation will contribute mucK to the 
 knowledge of this science. 
 
 After careful attention to details the airmen are 
 ready to ascend. Forethought is of great im- 
 portance to the aerial traveler and doubtless many 
 airmen have come to grief from a lack of it. The 
 temperature is nearly 100° Fahrenheit as the air- 
 men start for the aerial arctics. It is difficult to 
 conceive zero temperatures awaiting their arrival 
 in an hour or so; If their craft were of the most 
 powerful type they would reach an arctic zone in 
 an hour or two where the temperature is about 
 sixty degrees below zero. They take to the air 
 and begin their climb into the clear, deep blue sky. 
 
 Soon an elevation of one mile is reached and 
 their radius of vision has expanded to about 
 ninety miles. Eivers, lakes, and striking earth 
 areas fifty miles away may be seen easily and the 
 horizon of the ocean ninety mUes distant is clearly 
 visible against the blue-white horizon sky. 
 
 They continue to climb and when an elevation of 
 two miles is reached their range of vision is about 
 one hundred and thirty miles. They begin to ap- 
 preciate the comfort of arctic clothing, for the 
 mercury of the thermometer is hovering near the 
 freezing point. The view is one of those rare ones 
 of extremely high visibility, but despite the clarity 
 of the atmosphere some haze is present over the 
 land, for distance alone is not responsible for the 
 blurring of earth details near the horizon. 
 
 As they continue to ascend the thermometei; 
 
108 THE BOOK OF THE SKY 
 
 steadily falls and when they reach an altitude of 
 three miles it registers ten degrees above zero. 
 Their range of vision has extended to about one 
 hundred and fifty-five miles. Although the day is 
 very clear there is present a slight haze and now 
 a three-mile depth of this sunlit haze has spread 
 a thin white veil over the earth. All this time the 
 blue sky is becoming darker, for the white veil 
 below has been taken from the sky. Distant de- 
 tails of the earth's surface appear clearer than at 
 low altitudes because the obliquity of vision has 
 decreased. Yonder cape sixty miles distant ap- 
 pears but a short distance. The chief details of 
 its irregular coastline are plainly visible. The at- 
 mospheric pressure has decreased to about one- 
 half its value at the earth's surface, but they do 
 not notice the scarcity of oxygen because they are 
 not physically active. In the exertion of moun- 
 tain climbing the tourist becomes conscious of the 
 rarity of the atmosphere and accordingly de- 
 creases his exertions. But no such compelling 
 warning safeguards the airman. The rarity of 
 oxygen may merely make him languid or sleepy 
 and the possible results are easy to contemplate. 
 As the airmen continue their ascent experience 
 tells them that soon it would be wise to don the 
 oxygen helmets although by no means is it essen- 
 tial at this altitude. The temperature is steadily 
 falling and the cold wind striking their faces as 
 they peer over the edge of the cockpit pierces their 
 flesh. The slip-stream from the propeller directly 
 
A POLAR CLIMB 109 
 
 aHead of them, added to the actual air-speed of 
 the craft, makes a gale of more than one hundred 
 miles an hour. As they near their ' ' ceiling ' ' their 
 rate of climb decreases, owing to the decreased 
 density of the air. 
 
 They reach an altitude of four miles and the 
 thermometer registers below zero — colder than 
 the coldest days of winter at their locality. Their 
 range of vision has now expanded to one hundred 
 and eighty miles. The horizon of the ocean is 
 plainly visible at that distance, a different hue 
 than that of the horizon sky. The courses of sev- 
 eral rivers may be followed for one hundred miles 
 toward their sources in the indistinguishable 
 mountain range which is blended with the distant 
 horizon. These rivers empty into the bay many 
 miles apart but both their widened mouths are 
 plainly visible. A vast area of 100,000 square 
 miles (sixty-four million acres) of the earth's sur- 
 face lies within the circle of the horizon. Iowa 
 could lie completely in this circle and still cover 
 only about one-half the area. An island like Porto 
 Eico (3435 square miles) would cover only a small 
 portion of the area below them and the shimmer- 
 ing sea which bounds it upon aU sides would be 
 plainly visible at an average distance of about 
 forty miles. The combined land area of the Brit- 
 ish Isles is only slightly larger than the circle 
 bounded by their horizon at this altitude. Nearly 
 aL. the states of the United States could lie indi- 
 vidually within this circle and several of the 
 
no THE BOOK OF THE SKY 
 
 smaller states could be grouped within it at one 
 time. The vast range of vision is one of the won- 
 ders and inspirations of clondland. When one has 
 had opportunities to see in a single view many 
 miles of filigreed coast-line or the intricate pattern 
 of a river and its minor tributaries, he loses 
 respect for the accuracy of maps. Yonder cape is 
 not a rounded point; its coastline is a fringe of 
 delicate lacework of earth and water. Aerial 
 photography will aid the map-maker of the future. 
 The vastness of the field of vision leads the 
 imagination to demand more computations. (The 
 horizontal distance to the horizon is approxi- 
 mately equal to ninety times the square root of the 
 altitude in miles. At an altitude of seven miles 
 the horizontal distance to the horizon is two hun- 
 dred and forty miles. These are altitudes attain- 
 able by the aerial traveler, but from those forbid- 
 den heights above these, there must be wonderful 
 views, "What a price would one pay for a few 
 moments at an altitude of two hundred miles 
 above the central part of the United States with a 
 perfectly clear atmosphere beneath him, whence 
 he might see the Atlantic Ocean faintly shimmer- 
 ing under the rising moon and the Pacific Ocean 
 glowing in the rays of the setting sun. And while 
 on the wings of imagination, one might rise to an 
 altitude of 1500 miles whence his horizon circle 
 would nearly equal a great circle of the earth. 
 His line of vision when gazing toward the edge of 
 the distant earth would make an angle of about 
 
A POLAR CLIMB 111 
 
 forty-five degrees with the vertical. It may aid 
 visualization of such an imaginary view of the 
 earth to place the eyes three feet vertically above 
 a horizontal circle six feet in diameter. This circle 
 subtends approximately the same solid angle at 
 the eyes that the earth would when the eyes were 
 1500 miles above it. Imagine a map of the 
 Western Hemisphere drawn on this circle and that 
 as the eyes rove over it and leave its edge, they 
 look into the void of space. At any time except 
 near noon the observer at an elevation of 1500 
 mUes would see night and day simultaneously on 
 the earth. 
 
 If atmospheric conditions permitted his gaze to 
 penetrate toward that distant horizon of the earth 
 he might see the white ice-cap surrounding the 
 north pole, and the continent of North America, a 
 smaU area below him, dimmed and blued by the 
 depths of space and blended by distance into vel- 
 vety bluish gray, buff, and bluish green areas, 
 depending upon the distribution of seasons, and 
 touched here and there by the white of clouds. 
 Night and day would be visible simultaneously; 
 perhaps day over the Atlantic, dawn over the con- 
 tinent and moonlight over the Pacific. Perhaps 
 the eye would follow down this continent noting 
 the constriction at its southern end beyond which 
 expands another continent to the south. In the 
 dim distance of the far south a white area might 
 be a cloud-mass or the edge of the Antarctic polar 
 ice-cap. Surely the wonders of man's new world 
 
112 THE BOOK OF THE SKY 
 
 — cloudland — ^kindle the imagination and make 
 Jules Verne plausible. 
 
 In the foregoing views from unattainable 
 heights, a perfectly clear atmosphere is assumed. 
 The earth would still be veiled in the blue of clear 
 air. Under the conditions as they actually are, 
 the earth haze would add a white luminous veil so 
 that the details of the earth would be very much 
 befogged. 
 
 While the airmen enjoy the grandeur of the 
 extensive views, the craft mounts higher, but 
 slower and slower is its climb. It is approaching 
 its ceiling. The winds are very strong but the 
 craft bravely meets them, for it is headed into the 
 wind most of the time. If the speed of the air- 
 plane in still air is one hundred miles per hour, 
 it wiU just maintain its position in space if headed 
 directly into a wind of the same velocity. As the 
 airmen climbed they watched their drift and kept 
 the craft approximately vertically about a chosen 
 landmark. In doing so, they are conscious of the 
 approximate direction and velocity of the wind at 
 yarious elevations. 
 
 The temperature is steadily falling and the dark 
 blue sky apparently emphasizes the cold. The un- 
 tempered sun breaking through the dark sky casts 
 harsh dark shadows like those xinder a lone street 
 lamp at night. The sky which is ordinarily bright, 
 chiefly by virtue of the illuminated dust or haze, is 
 now so free from such particles that it appears 
 like a transparent blue-black. The brighter area 
 
A POLAE CLIMB 113 
 
 of sky near the sun, as is commonly noted wlien 
 viewed from the earth, is no longer conspicuous. 
 The faint brightness of the canopy above is that 
 pure blue of space, the source of which is still in 
 doubt. Through this darkness amid the piercing 
 cold of the arctic temperature, the sun's rays ap- 
 pear to come without their usual heat. The cres- 
 cent of the moon, which seen from the earth is 
 barely brighter than the sky, now shines more 
 brightly amid its dark blue surroundings. Per- 
 haps, if the airmen look carefully, they wiU dis- 
 tinguish some of the more brilliant stars because 
 they are always awaiting behind the haze-veil of 
 the daytime sky. 
 
 The airmen are now in the region of mackerel 
 skies. They are in the realm of perpetual cold. 
 Here the filmy clouds consist always of floating 
 ice. This indeed is a polar clime and still only a 
 short distance from the earth and summer 
 [weather. The distance is about one hour up and 
 ten minutes down. 
 
 The airmen realize that the craft is very slowly 
 ascending and that their ceiling lies somewhere 
 between four and five miles. Higher altitudes 
 offer more experiences but, after aU, what is a 
 mile or two or three higher when space extends to 
 infinity I Man's invasion of the air has opened the 
 wonders of a new world to him. The scanty film 
 of space a few miles in thickness of which he is 
 now master is a spacious wonderland when com- 
 pared only with earthly dimensions. Man has 
 
114 THE BOOK OF THE SKY 
 
 personally ascended in this sea of space to an alti- 
 tude of about eight miles above the level of the 
 oceans, and inasmuch as clouds do not extend 
 much higher, he is in reality master of cloudland. 
 He has flown kites to altitudes of about five miles. 
 In the study of meteorology he has sent up bal- 
 loons with recording apparatus to about twenty- 
 two miles. Small balloons without apparatus have 
 attained elevations of about twenty-five miles. At 
 these highest altitudes from which mankind has 
 obtained data directly, the atmospheric pressure 
 and density are less than one per cent of their 
 values at sea-level. Eare as it may be at the high- 
 est level explored, there are many reasons for 
 suspecting that atmosphere stUl exists, though ex- 
 tremely rarefied, at altitudes up to one hundred 
 miles at least. 
 
 Up in those regions where the last vestiges of 
 the earth's atmosphere are dying away and that 
 infinitude of frigid emptiness begins, there are 
 other phenomena to interest mankind. The twi- 
 light limit is somewhere below one hundred miles, 
 and the region above thirty miles and below one 
 hundred thirty miles is that where the "shooting 
 stars" stage their pyrotechnic displays. Sur- 
 mounting these, sometimes at altitudes as high 
 as five hundred mUes, are the mighty auroral arcs. 
 These restless shifting curtains, streaks, bands, 
 and arcs are the electrical effects of the heavenly 
 stage. Thus it is seen that the wonders of space 
 never cease. Cloudland is full of interest, but as 
 
A POLAR CLIMB 115 
 
 one mounts higher and higher on the wings of the 
 imagination, wonders of greater magnitude un- 
 fold without end. The aurora is the last visible 
 phenomenon associated with the earth, but farther 
 and farther into the infinitude of space, events of 
 tremendous magnitude are taking place. 
 
 Thoughts of these wonders above them occupy 
 the minds of the airmen as their craft battles 
 against wind and gravity. For some time the alti- 
 meter has appeared stationary; evidently the 
 faithful craft has reached the limit of its powers. 
 The actual altitude is of no great interest here, 
 but it is between four and five miles. The tem- 
 perature is fifteen degrees below zero Fahrenheit. 
 
 One of the airmen looks toward the other with ^ 
 significant sign and apparently there is agree- 
 ment. The motor is throttled and the craft dips 
 suddenly downward. For a moment the airmen 
 have the feeling that the craft is leaving them. 
 Downward they glide at a steep angle; the craft 
 tilts to a steep bank; and with controls set in just 
 the correct position the craft describes a helix of 
 email diameter and large pitch. This is misnamed 
 a close or tight spiral. The thousands of feet are 
 clipped off rapidly as they descend steeply and 
 dizzily as they "spiral." The plane of the earth 
 ;wobbles as though it were on a stormy sea. For 
 minutes this descent continues, then to relieve the 
 monotony and seemingly to "unwind" their some- 
 what confused vision, the controls are thrown over 
 to another position and the "spiral" is reversed. 
 
116 THE BOOK OF THE SKY 
 
 The wobbly whirl goes on for minutes which would 
 seem an eternity to one who is not a good sailor. 
 The close "spiral" is chosen as a fast and safe 
 mode of descent because the course of the path is 
 such as to insure against the attainment of unsafe 
 velocity. The craft does not tend to accelerate as 
 it surely does in a nose-dive, but it attains a con- 
 stant and safe speed of descent determined by the 
 angle of the craft and consequent air-resistance. 
 
 Down and down they continue their descent 
 xmtil suddenly they become conscious of a much 
 warmer temperature. They are only a few thou- 
 sand feet from the earth. Their goggles are 
 steamed over, their faces feel damp, and every- 
 thing their hands touch seems covered with mois- 
 ture. The cold temperature attained by these ob- 
 jects at the high altitudes accounts for the conden- 
 sation of water-vapor in the more humid lower at- 
 mosphere. Shortly they glide to rest safely on the 
 ground. They feel uncomfortable in the heat of 
 midsummer and it already seems as if they had 
 dreamed that their thermometer registered zero 
 ten minutes ago. This polar climb has not been 
 filled with the beauties of some other flights but it 
 has supplied some wonderful views. It has awak- 
 ened the imagination and has pointed the way to 
 new avenues of thought. In fact, it was a trip 
 worth including in the itinerarjr of the sojourner 
 in cloudland. 
 
CHAPTER XII 
 
 CLOUD CAPEES 
 
 "Heavenly clouds who supply us with thought and 
 argument and intelligence and humbug and circumlocu- 
 tion, and ability to hoax, and comprehension." 
 
 — ^Abistophanes. 
 
 THE antics of clouds and their ever-changing 
 forms have been touched upon throughout 
 this little volume but it is hoped a few random 
 notes will not be unwelcome. Their sudden ap- 
 pearance and disappearance so appropriate to 
 their spirit-like texture and to their invisible 
 world, their restlessness, their endless variety, 
 make it easy for one to become deeply absorbed 
 in this aspect of the heavens. The aerial traveler 
 need not be alone when clouds are in the sky. 
 A scene need not become monotonous if one 
 but looks to the moving clouds, and if one does 
 not like the scenery of the moment he needs 
 only to await the scenery of another moment. 
 Amid the day's work an open window and a 
 patch of sky will afford an escape from the rou- 
 tine grind. Everywhere and at all times except 
 on those rare cloudless days the clouds are per- 
 il? 
 
118 THE BOOK OF THE SKY 
 
 forming for observant beings. Their manifold 
 forms and modifications arouse the fancies and 
 impress one with the conviction that thqy are try- 
 ing to tell mankind much that he does not know. 
 To describe these endless capers would be a task 
 as long as eternity, but to attempt to give an idea 
 of these antics is a short and pleasant recreation. 
 These few paragraphs, then, are merely represen- 
 tative of this aspect of clouds. They are garnered 
 chiefly from recent casual observations of the sky 
 which are fresh in memory. 
 
 It is a clear summer morning and dew sparkles 
 in the grass. At first not a cloud appears in the 
 isky but in an hour or so as the sun evaporates the 
 dew, thin clouds appear. The dew now floats in 
 the sky whence it came during the night. The 
 ascending currents have carried this evaporated 
 dew to regions where it becomes sufficiently cooled, 
 chiefly by expansion, to lower the temperature of 
 the air below its dewpoint and, therefore, clouds 
 are formed. At first these are thin but rapidly 
 they become larger. If one lingers over his work 
 for a time he may be surprised to note as he 
 glances skyward in an hour or so, that a vast flock 
 of fair-weather cloudland has come into being. 
 Eyes cannot see the whole process of evolution 
 but the mind may see what they do not. 
 
 Yesterday at noon the crests of the fair-weather 
 cumulus clouds were leaning forward as though 
 they were anxiously straining to move faster than 
 the wind. Today their crests are leaning back- 
 
CLOUD CAPERS 119 
 
 ward as though, they are reluctant to go whither 
 the winds cominanded. Their attitude of yester- 
 day is perhaps the more common of the two. 
 Cumulus clouds are formed by vertical convection 
 currents, the fair-weather type being formed 
 chiefly by mild differences in temperature between 
 adjacent bodies of air. As the heated air rises, 
 some of the moisture condenses and condensation 
 continues as the air ascends. Hence the clouds 
 have considerable depth and appear like heaps. If 
 the wind at the level of their crests is of sufficiently 
 higher velocity than that of the stratum of their 
 bases, the crests will strain forward. If of suffi- 
 ciently lower velocity, the crests will lean reluc- 
 tantly backward. If the difference in the two 
 velocities is sufficient, the clouds may be torn into 
 fragments ; hence, this is one source of the f racto- 
 cumuli which often go racing by. Thus, simple 
 observations may lead from one to another and 
 thereby uncover much pertaining to the air. It 
 is interesting to picture in the mind's eye the 
 invisible currents and their influence upon one 
 another. 
 
 Toward the close of the day the upward con- 
 vection currents grow weaker and weaker with the 
 result that the cumulus clouds become flattened or 
 even like stratus. This is the reason for the lower 
 stratified clouds of last evening's sunset. 
 
 Sometimes a sudden weakening of the upward 
 current which supports the cumulus cloud in its 
 beautiful rock-like shape, results in a striking 
 
120 THE BOOK OF THE SKY 
 
 formation variously called globo-cimiulus, pocky 
 cloud, festooned cloud, and mammato-cumulus, 
 the last name being official. The lower side of the 
 cloud bears an appearance something like flat 
 globules of water clinging to the lower side of a 
 horizontal surface such as a ceiling of a room. 
 These have been called "rain-balls" because their 
 rare occurrence is generally in connection with a 
 thunderstorm. Suppose very cold air or even 
 snow drifted out of the top of a thunderstorm over 
 a thin stratus cloud. This cloud would be cooled 
 and would begin to sag in spots and there must be 
 rises interspersed between the sags. Thus the 
 shapes of these clouds may be accounted for. 
 When these festoons appear just before sunset as 
 they did recently, thus receiving reddish light 
 from underneath, their beauty can hardly be sur- 
 passed in cloudland. 
 
 A few days ago the cumulus clouds floating over 
 the water were small and rather flat. The morn- 
 ing was hot and the cumulus clouds over the land 
 were rearing strongly upward. As the clouds 
 drifted from over the water and reached a position 
 vertically above the shore, they were torn vio- 
 lently and rapidly upward in a variety of shapes, 
 and all were tattered as the result of the rough 
 treatment. This performance went on for hours 
 and clearly demonstrated to the observer the su- 
 perior strength of the upward currents over the 
 land, which, of course, was hotter than the water. 
 These capers of the clouds were exceedingly fas- 
 
CLOUD CAPERS 121 
 
 cinating botH from tlie viewpoint of beauty and 
 technical interest and furnisbed an endless variety 
 of rapidly changing forms. 
 
 Cumulus clouds often may seem to be stationary 
 for hours despite the gentle breeze which may be 
 blowing and a question arises as to how they 
 maintain their position against a breeze. The 
 ascending convection currents, once formed, seem 
 to maintain their position with respect to the 
 earth to some extent against the surface wind. 
 The ascending air with its load of water-vapor is 
 cooled chiefly by expansion as it reaches the higher 
 levels and some of the moisture condenses and 
 replenishes the cloud which is evaporating on its 
 crest and on its leeward side. In other words, the 
 cloud is being formed as rapidly as it is drifting 
 in the wind and being evaporated. 
 
 Another example of stationary cloud is found in 
 the clouds of the mountain top. The moist air of 
 the lowlands is driven up the mountain side and 
 condensed in this cooler and rarefied region. The 
 cloud thus formed is constantly moving with the 
 wind and evaporating, but is also continuously 
 replenished. Depending upon the velocity of the 
 wind and upon other factors, the cloud may cover 
 the crest like a mantle ; it may hover over it like 
 a sun-shade; it may maintain a position to the 
 leeward; or it may wave from the peak like a ban- 
 ner. 
 
 A similar case was witnessed on many aerial 
 trips over a vast swamp containing several hun- 
 
122 THE BOOK OF THE SKY 
 
 died square miles of low waste land in the center 
 of which, was a small lake two or three miles in 
 diameter. A low fringe of clouds often hovered 
 over one side of the lake when the rest of the sky 
 and landscape was cloudless. These clouds were 
 so often found that their occasional absence be- 
 came a disappointment. 
 
 Mariners have often "sighted" an island in the 
 midst of an ocean long before it appeared on the 
 horizon by the lone cumulus cloud which hung 
 above the horizon. Such a cloud-cap floating 
 above an island is a common observation. Despite 
 the wind that is blowing it maintains its position 
 even though it is also drifting with the wind, for 
 as fast as it drifts away and is evaporated on one 
 side it is being replenished by the moist air as- 
 cending from below by virtue of its higher tem- 
 perature and consequent lesser density than the 
 surrounding air. 
 
 Cumulus clouds are most easily observed owing 
 to their size and proximity to the earth, although 
 these features are disadvantages when such 
 clouds are overhead. In this position their gray 
 flat lower surfaces are uninteresting and conceal 
 their beautiful forms. The rearing cumulus 
 which stations itself over toward the horizon, but 
 not too far away, is conferring a favor upon man- 
 kind which is not generally enough appreciated. 
 Sometimes the entire evolution of a thunderstorm 
 may be seen and when the opportunity is thus 
 advantageously presented it is deplorable that 
 
CLOUD CAPERS 123 
 
 mankind does not observe these most majestic of 
 all aerial sculptures. 
 
 Cumulus clouds of higher altitudes, the alto- 
 cumuli, are smaller than the cumuli proper but 
 larger than the cirro-cumuli of still higher regions. 
 These are generally globular but assume a variety 
 of forms too numerous to describe. They are 
 usually in flocks, shepherded by the winds into pat- 
 terns and long columns. Their formations are 
 confusing to the earthly observer owing to the illu- 
 sions of perspective, but the aerial traveler be- 
 comes very familiar with their forms and levels. 
 
 On a quiet day the upward convection currents 
 are robbed of some of their moisture and the 
 cumuli are formed. The air may continue to 
 ascend and on reaching a stratum of air of suffi- 
 ciently low temperature and high humidity, some 
 more moisture may be condensed. This cloud 
 which would not be dense is left behind and at a 
 higher altitude the process may be repeated. In 
 this manner some of the clouds of various levels 
 may be accounted for, especially in fair weather. 
 
 On nearly every day when several varieties of 
 clouds are in the sky, one may watch a group 
 speeding confidently past only to vanish in thirsty 
 air. Thus a clear area beyond may be continu- 
 ously fed with clouds from the supply to the wind- 
 ward. 
 
 One morning a few days ago the entire heavens 
 were overcast by a beautiful pattern of billowed 
 cloud, symmetrical in two directions approxi- 
 
124 THE BOOK OF THE SKY 
 
 mately at right angles. If one happened to be a 
 close observer of wind-patterns on water or of 
 the effect of a cross-current upon a drifting layer 
 of smoke he might be able to visualize the mechan- 
 ism which formed those beautiful bUlows. This 
 effect may be seen in the smoke-stream from a 
 steamer which is traveling at an angle to the 
 direction of the wind. The airman at the level of 
 the billowed cloud sees huge waves sometimes hun- 
 dreds of feet vertically between the levels of crest 
 and trough respectively. He notes as he rises 
 through this region that one current of air is over- 
 running another current. The interaction of these 
 form the billows as explained elsewhere. These 
 effects take place at all levels, — from fog to high 
 cirrus levels, — Whence the vast variety of patterns 
 of the high clouds. 
 
 ~ The stratus clouds are not beautiful but they 
 add at least color to the sky as they lie now in 
 bright sunlight and again in blue shadow. They 
 are found at all levels. Sometimes they are 
 broken or of varying density and are responsible 
 for some of the delights of a quiet moonlit night. 
 One may see them form if closely observant. They 
 are often formed by a layer of cold air under- 
 running or sliding, as it were, underneath a humid 
 layer. Inasmuch as this may take place at any 
 altitude, the stratus clouds may be formed at any 
 level. They predominate, however, at certain 
 levels as indicated in other chapters. When the 
 
CLOUD CAPERS 125 
 
 air is fairly still it is easy to note their appear- 
 ance and growth. 
 
 A few evenings ago the sky was perfectly clear 
 and the moon was already high. Suddenly, at 
 least it seemed so, a thin layer of cloud appeared 
 which rapidly grew to a fair density. No drift 
 could be detected and inasmuch as the air seemed 
 stni even at the altitude of this cloud-sheet, which 
 was probably a half mile, the cloud seemed to 
 have been formed in its position. This could have 
 been the result of cooling in place by loss of heat 
 after the sun had set, or by other undisturbing 
 means. 
 
 A few days ago a vast array of fair-weather 
 cumulus appeared in the sky about the middle of 
 the morning. They were lazily floating and of the 
 strictly heaped formation, though not large. The 
 breeze gradually grew to a stiff wind and the tem- 
 perature lowered. In the course of an hour those 
 fluffy cumuli had flattened to forms resembling 
 ragged cakes of ice. The area over a large body 
 of water was perfectly clear, but down the sky 
 over the land these flattened cumuli marched in 
 disorder. Huge mountains of clouds to the wind- 
 ward disappeared and these small cumuli faded in 
 two hours, leaving a perfect, cloudless sky. The 
 majestic disorder of these clouds, their rapid 
 change of form, and their gradual disappearance 
 are inadequately described in words, but it was a 
 sky worthy of occasional glances at least. Surely 
 the Creator erred in supplying such attractions 
 
126 THE BOOK OF THE SKY 
 
 so often. Occasional appearances doubtless would 
 result in more appreciation of the marvels of 
 cloudland. 
 
 Late in the afternoon yesterday the heavens 
 contained a large variety of clouds at several 
 levels even to the high cirri. It seemed as if there 
 were a general clean-up going on. It was one of 
 those conditions that the observer of the sky and 
 the appreciative air-traveler longs for, not only 
 for the variety of interest in the clouds themselves, 
 but their multi-forms and various levels late in 
 the day give assurance of a riotous sunset. The 
 most gorgeous sunsets depend for their effects 
 upon clouds at several levels. True to precedent, 
 the sunset an hour or two later was of the best 
 that autumn can produce. Incidentally, it seems 
 that autumn is the season of wonderful sunsets. 
 The pastel tints of this season were lavished with 
 masterful genius upon the clouds of many forms 
 at various levels, from low bits of flattened cumuli 
 to the highest cirri. These clouds as they alterv 
 nated in and out of the sunlight, first in cold-tinted 
 shadow and then in warm-tinted sunlight, con- 
 spired to make a spectacle of riotous splendor. 
 "When clouds are dispersed in this manner in late 
 afternoon, one learns to look for a sunset which 
 is well worth an unobstructed view. 
 
 Among the most fascinating clouds are the tow- 
 ering cumulo-nimbus or thimderheads. Their 
 vigorous turbulence indicates powerful upward 
 currents. As these rear higher and higher their 
 
CLOUD CAPERS 127 
 
 crests become more and more interesting. During 
 midsummer one of these towering giants of cloud- 
 land took up a position about ten miles away and 
 gradually extended itself until its crest reached an 
 altitude of several miles. During this rise, a thin 
 cloud formed above its head and as the crest rose 
 this thin veil appeared to drape over it. As the 
 head rose higher it left the thin cirrus-like cloud 
 behind. Seen from the heights, this cloud re- 
 sembles a thin fog obscuring the crest for a time 
 until the latter forged upward through it. While 
 watching this huge thunderhead from an altitude 
 two miles above the lower ordinary cumuli, the 
 intricate details were easily analyzed without the 
 confusion attending the view from the earth, 
 owing to perspective. However, the illusions of 
 perspective are not as confusing for towering 
 cumuli when they are at a proper distance as for 
 the thinner clouds of extreme heights. Later as 
 viewed from the ground, several fragments 
 seemed to break loose from the crest of the thun- 
 derhead and went drifting rapidly away. Casual 
 observation does not reveal the rapid changes 
 which take place in the turbulent crests of these 
 towering cumuli. If one needs to be convinced let 
 him take a number of photographs at intervals of 
 two or three minutes. 
 
 Although all clouds afford a variety of interest, 
 the cumuli doubtless furnish the most attractive 
 individual antics. They are large and often close 
 enough to be in the same air-current which 
 
128 THE BOOK OF THE SKY 
 
 brushes the earth's surface. Their origin is 
 clearly established and all their details are easily 
 understood. For these reasons they afford excel- 
 lent objectives for the observer of cloud antics. It 
 appears hopeless to invade the field of high clouds 
 in this chapter for, although their rapidly chang- 
 ing forms are exceedingly interesting, relatively 
 few would care to read the more involved explana- 
 tions which, owing to the less general acquaint- 
 ance with these clouds, are not easily visualized 
 from verbal descriptions. The purpose of the 
 chapter is attained, however, if by a few common- 
 place examples, it has given the reader a glimpse 
 of another viewpoint or attitude toward the 
 clouds. 
 
 Occasionally tufts or veils are to be seen hang- 
 ing from compact masses of high clouds. Some- 
 times these are showers of rain or snow taking 
 place in the heights of cloudland. They may be 
 evaporated by thirsty air before falling far. At 
 other times they may be merely streamers pulled 
 out by the winds. They may actually be hanging 
 downward or they may merely appear to be pen- 
 dent due to an illusion of perspective. 
 
 The terms "canopy" and "dome" as applied to 
 the sky do not arise from pure fancy. As one ob- 
 serves the heavens he becomes conscious of an illu- 
 sion of the sky which makes it appear like a dome. 
 Whether this illusion is due to a suggestion of a 
 dome shape by the sky itself or arises from our 
 own inner reasoning, the author is unable to de- 
 
CLOUD CAPERS 129 
 
 termine ; however, it is a recognized illusion. In 
 fact, experiments have been made to determine 
 the apparent shape of the sky dome as it appears 
 to groups of observers. The results indicate that 
 most persons would consider it a flattened dome, 
 that is, not a true hemisphere. 
 
 One cannot observe the clouds for entertain- 
 ment without thinking occasionally of their useful 
 function. They visibly represent the moisture in 
 the vast sea of air above the earth. As the air- 
 man travels through the transparent atmosphere 
 he is rarely conscious that he is also passing 
 through water-vapor. Ofttimes in this transpar- 
 ent air there is more moisture in a given volume 
 than in the same volume of clouds, but this water- 
 vapor before it falls to earth must pass through 
 the cloud stage. Hence, clouds are the vehicles 
 which sprinkle the earth with rain. A surprise 
 awaits those who would compute the weight of 
 water which yearly is evaporated from the earth 
 and returned to it again by way of the clouds. The 
 total weight of water spread over an acre of 
 ground to the depth of one inch is about one hun- 
 dred tons. In regions where the yearly rainfall 
 is fifty inches, the water delivered by the clouds 
 per year upon an acre of the earth's surface is 
 approximately five thousand tons. The total ton- 
 nage of a fifty-inch rainfall over a square mile is 
 more than three million tons. The total tonnage 
 of water deposited yearly by the clouds upon the 
 state of Iowa is approximately One hundred fifty 
 
130 THE BOOK OF THE SKY 
 
 billion tons. The tonnage for tlie United States, 
 is represented by an incomprehensible number and 
 for the entire earth proportionately larger. This 
 gives another glimpse of the magnitude of the 
 scale upon which Nature operates. It helps one 
 to comprehend the existence of the mightiest 
 storm which is really a pigmy in Nature's scale. 
 It kindles one's imagination regarding the great- 
 ness of cloudland and the immensity of the 
 meteorological scheme which is carried out in this 
 region. And after all, the clouds and winds are 
 law-abiding and do their parts as assigned to them 
 by those conditions which rule them. 
 
CHAPTER XIII 
 
 A NIGHT FLIGHT 
 
 "Now black and deep the Night begins to fall, 
 A shade immense! Sunk in the quenching Gloom 
 Magnificent and vast, are heaven and earth." 
 
 — Thomson. 
 
 THE last blush of tlie fading sunset lingers in 
 the sky. Already at their outposts the sen- 
 tinel stars have set their watch in the heavens to 
 be reinforced as darkness deepens. Two airmen 
 sit patiently contemplating the approach of night, 
 their aircraft dimly outlined on the field before 
 them. One might readily imagine that it, too, were 
 waiting. Night flying has not the variety to make 
 it as appealing as flying by day, but the mood of 
 night in cloudland is so powerful that an occa- 
 sional flight by night is worth while. Over near 
 the horizon lightning flashes reveal momentarily 
 a low-lying range of cloud-mountains, a bluish 
 white with steely blue shadows, so cold compared 
 with the glowing crests by day. As darkness 
 spreads its pall, myriads of stars stud the sky 
 overhead. 
 J'he field lights burst forth and reveal the two 
 
 131 
 
132 THE BOOK OF THE SKY 
 
 airmen boarding their craft. The engine ig started 
 and allowed to warm np. The roar gradually 
 increases and finally dies down, almost a sure sign 
 that the blocks are being removed and the craft 
 is to begin its journey aloft. A spurt or two and 
 the craft speeds down the field soon to be lost in 
 darkness except for its tiny lights. For the air- 
 men the illuminated field rapidly dwindles to a 
 dimly lighted patch. At an elevation of a thou- 
 sand feet the earth is but the faintest ghost of 
 itself. The dull earth of daytime is now weirdly 
 enchanting. As the airmen mount higher and 
 higher nothing is definitely visible below except 
 civilization's lights. They have no horizon to aid 
 them in keeping an even keel, but the lights in the 
 distance are far enough away to serve the pur- 
 pose of a horizon until they are above the haze. 
 
 A feeling of loneliness creeps over them only to 
 be suppressed again by the grandeur of the starry 
 night. The sky is full of company, distant though 
 the stars may be. Space is not the lonely solitude 
 that it is by day when only the sun inhabits the 
 blue. The haze which cannot be seen is effective, 
 however, for the stars diminish in number toward 
 the place where the horizon should be. Far ahead 
 is the subdued glow of a distant city. Below a 
 tiny beam of light marks a train guided through 
 the darkness by its path of steel. In the distance 
 the lightning still continues to illuminate spas- 
 modically the vaporous crags of the cloud-moun- 
 tains, revealing the rendezvous of Jove and his 
 
A NIGHT FLIGHT 133 
 
 coliorts. The airmen turn the craft toward that 
 flashing range and continue to mount higher. As 
 the earth lights grow dimmer, the stars grow 
 brighter. They are leaving the earth's haze 
 behind them. 
 
 An altitude of five thousand feet is reached and 
 the black sky is studded with brilliant stars over 
 its entire hemisphere. The horizon is indicated 
 by an invisible boundary of the starry heavens. 
 Above the earth haze the brilliance of the nmnber- 
 less stars is unimpaired. There is grandeur, 
 magnificence, aiid infinitude in the apparent lack 
 of order in their arrangement. They lie in such 
 Confusion that the inability to estimate their num- 
 ber leaves one with an impression of infinity. 
 Some one has called the sky, twilight's curtain. 
 Imagination suggests that these stars are pin- 
 holes in the curtain and that Day is concealed 
 behind it. 
 
 As the aircraft mounts higher and approaches 
 the distant storm, indescribable feelings of awe 
 overtake the airmen. The storm with all its ma- 
 jestic turbulent clouds is an awesome sight in the 
 daytime when its lightning flashes are feeble. But 
 the mood of night adds to the mystery, the magni- 
 tude, the intensity, the effectiveness of many 
 events, especially storms. To the airmen all the 
 powers of the daytime storm are multiplied by the 
 strangeness and possible dangers of flying at 
 night. But men who have felt the thrills of cloud- 
 land and who have known the inspirations of fly- 
 
134 THE BOOK OF THE SKY 
 
 ing could not turn away from even the over- 
 whelming awesomeness of this brilliant electrical 
 display, as, 
 
 "Far along 
 From peak to peak the rattling crags among 
 Leaps the live thunder." 
 
 — Bykon. 
 
 As they approach closer they recognize, during 
 the flashes, the same characteristics of a thunder- 
 storm by day. AU around, above and below, is 
 darkness pierced only by faint points of light com- 
 pared with the brilliance of the flashes which 
 illuminate the clouds for miles beyond. Witli each 
 flash they and their craft are brilliantly illumi- 
 nated. They see part of the course and almost the 
 source of some of the flashes. Now a crooked lance 
 of brilliant steel-blue light darts from cloud to 
 cloud. Another shaft starts from near a peak and 
 is visible for only a short distance through an 
 opening in the clouds. The light from each lance 
 is reflected here and there among the crags in the 
 abysmal depths producing a display whose mag- 
 nitude, whose awesomeness, whose magnificence, 
 words cannot describe. 
 
 In "the dead vast and middle of the night," 
 alone in space nearly ten thousand feet above the 
 earth, they witness a splendid spectacle. Their 
 friends at home in the distance who see only the 
 flashes faintly in the distant sky perhaps casually 
 mention "heat lightning." This is "heat light- 
 
A NIGHT FLIGHT 1S5 
 
 ning," tliat is, lightning of a storm out of sight 
 near or below the horizon. The airmen think of 
 those below upon whom the storm is bestowing the 
 blessing of rain but demanding its pay in the 
 devilish pleasure it probably gains from the terror 
 instilled by those brilliant lightning flashes and 
 accompanying roars of thunder. 
 
 The two airmen high above those scowling, 
 flashing, thundering clouds are not cringing in 
 terror. They strain forward in their seats wholly 
 absorbed by the magnificent splendor. Awe is the 
 nearest approach to fear among the gamut of emo- 
 tions which they experience. They are out of 
 reach of the storm and this feeling of supremacy 
 does not escape them. They are taking chances, 
 for the few risks of flying by day are multiplied 
 at night. But they are unafraid, for their phi- 
 losophy has long ago put them at ease. They have 
 lived long in their hours in cloudland. To them 
 living is measured in terms of intensity and the 
 intensity of living during the past hour would 
 cover many days of every-day living if spread out 
 to ordinary thinness. 
 
 During this time they have soared back and 
 forth viewing the flashing vaporous range from 
 various angles, but always out of reach of the 
 storm. Such storms by night do not usually extend 
 to such high altitudes as the exceptional thunder- 
 head of the daytime storm. They leave this spec- 
 tacle with the greatest reluctance, for it fascinates 
 them as the abysmal canyon draws the fearsome 
 
136 THE BOOK OF THE SKY 
 
 tourist to its edge. They turn back toward home 
 guided by the stars although the luminous com- 
 pass before them would show the way. However, 
 the stars are more convenient; that "glorious host 
 of light" is the infallible guide of the traveler in 
 uncharted places. Above them the constellations 
 describe their heavenly paths in definite and es- 
 tablished order around Polaris. This North star, 
 toward which the axis of the earth very nearly 
 points, appears fixed, hence, it is the pivot around 
 which the constellations swing. 
 
 As the airmen soar homeward they note a beam 
 'of light swinging around the space below them. 
 They follow its bright patch from the earth to a 
 level far below them above which it appears to 
 weaken. Suddenly they are blinded by a powerful 
 light, but only momentarily. It is a searchlight 
 in quest of them, for the crew has heard the purr 
 of their motor. Their high speed took them out 
 of the beam before the crew of the searchlight 
 realized that the tiny speck was the object of their 
 search. There is another blinding flash as the 
 beam is turned full upon them again. This time 
 they are held in the beam. The searchlight is 
 miles away but it illuminates their craft so that 
 they read their instruments without turning on 
 their lights. The beam leaves them and sweeps 
 through the heavens. For an instant the black 
 clouds they have left are faintly brushed by the 
 beam. One of the clouds is many miles distant 
 from the searchlight, but here is an example of 
 
A NIGHT FLIGHT 137 
 
 some of the possibilities of searchlight signaling. 
 By flashing a code-message on a distant high 
 cloud, observers far below the horizon have read 
 the message at a distance of a hundred miles. 
 
 The airmen have left the storm far behind them. 
 In the distance lies the subdued glow of a city, its 
 light diffusing faintly over a large area of the 
 haze below them. What a variety of different 
 colors are to be seen below them in the lights of 
 civilization, but all dulled and reddened somewhat 
 by the haze. They drop lower and lower in a safe 
 glide. No stunts tonight because the quickness of 
 judgment requires conspicuous reference lines, 
 such as the horizon or the circle of earth for 
 stunting. Down they come to an altitude of five 
 thousand feet. The beam from the searchlight 
 still swings through the heavens, now and then 
 brightening at its upper end as it brushes a filmy 
 cloud and illuminates it. As it swings in a wide 
 arc before them it appears to be reduced to a 
 fainter pencil above this level. From experience 
 and a few indications they conclude this is the 
 upper level of the earth haze, that is, the upper 
 limit of the diurnal convection currents. A 
 searchlight beam is luminous only when it has 
 some reflecting media to illuminate. The dust 
 particles of the haze make the beam luminous just 
 as the path of a sunbeam in a dusty atmosphere of 
 a room is luminous. Above this low-lying earth 
 haze, which often has a definite upper limit at an 
 altitude of five or six thousand feet, the reflecting 
 
138 THE BOOK OF THE SKY 
 
 particles in the atmosphere are usually much less 
 numerous than in the lower haze. Consequently, 
 the beam of the searchlight appears to diminish 
 in brightness at this level. On occasions when 
 there is no defined upper limit of the haze, the 
 beam appears brilliantly luminous to much greater 
 heights, often stopping in a bright spot as it en- 
 counters filmy clouds of the high altitudes. 
 
 The airmen continue their descent and now 
 their adapted eyes are able to perceive black 
 patches amid areas of dark grays. The shapes are 
 uncertain and fantastic. Tiny pairs of lights pass 
 along in a straight line far below them. They are 
 automobile headlights guiding families home from 
 their evening's recreation. The automobile is a 
 wonderful development from which mankind is 
 gaining much pleasure and recreation, but the air- 
 men cannot help comparing their evening's experi- 
 ence with those enjoyed by the earthly travelers 
 in the wake of those tiny pairs of lights. They 
 are nearing the ground and must approach cau- 
 tiously because wires, poles, and trees must be 
 avoided. The field lies yonder bathed in its flood 
 of light. They circle to the leeward and descend 
 cautiously with eyes more intent upon the earth 
 than in the daytime. Its distance must be gauged 
 accurately and the illusions of night must be 
 avoided. They glide toward the ground straight- 
 ening out cautiously. The wheels touch the 
 ground, then the third point, and the craft glides 
 
A NIGHT FLIGHT 1S9 
 
 over the grotmd. They taxi back to their hangar 
 and dismount. 
 
 As they walk homeward they compare impres- 
 sions of the evening's experiences, for they could 
 not converse aloft and sign-language was useless 
 in the darkness. They try to express their feel- 
 ings and emotions while witnessing the storm, but 
 both agree that it "can't be done." No one can 
 do it justice, that is certain. Night flying has its 
 risks but those who live in the present age with 
 its aerial craft that can take them to such scenes 
 in the environment of the mood of darkness, have 
 not fully lived until they have seen them. After 
 such an experience there will be a fuller meaning 
 in Byron's words: 
 
 "Most glorious night! 
 Thou wert not sent for slumber!" 
 
CHAPTEE XIV 
 
 ANNIHILATING DISTANCE 
 
 "So it is in traveling: a man must carry knowledge 
 with him, if he would bring home knowledge." 
 
 — Sam'l Johnson. 
 
 TT is a bright cloudless sinrimer morning and 
 -■■ two men of the air are astir early, for they 
 have business to transact in a city two hundred 
 mUes distant as the crow flies. But distance in 
 these modern times is indefinite when measured in 
 miles. Its true measure is in time and perhaps 
 in convenience. In this sense distance varies with 
 the means of travel and with the coordination of 
 the various kinds of transportation. To arrive in 
 that distant city in time to begin the business day 
 would ordinarily require a night spent on board 
 a steamship or train. Instead, the airmen spend 
 it at home. 
 
 The aircraft is brought from its hangar and 
 tuned up. The airmen test the tautness of a wire 
 here and there ; they examine struts and give the 
 tail a casual shake. As the engine is warming 
 up they take their seats in the fuselage and lei- 
 surely stow away their light baggage. One of 
 
 140 
 
ANNIHILATING DISTANCE 141 
 
 them opens the throttle and notes how the engine 
 "turns over." At a nod of his head the blocks 
 are cleared away and with a shake of the "joy- 
 stick" to see that the controls are clear, the 
 throttle is opened wide. Down the field the air- 
 craft gains speed, the taU rises from the ground, 
 and the mechanical bird takes to the air. In a few 
 minutes the field is far below and behind them 
 and the craft is on its way boring into the blue 
 toward a certain point of the compass. 
 
 On the instrument boards in front of them are 
 maps of the state across which they are to fly to 
 that city two hundred miles distant — ^two hours 
 barring adverse winds. They mount upward and 
 upward until ten thousand feet is reached, and 
 there unfolds before them a large portion of the 
 Btate. At this altitude their radius of vision is 
 one hundred and twenty miles. The landmarks 
 are not red schoolhouses and crossroads. They 
 look ahead and see two large rivers and, yes, 
 there is the third one barely visible under what 
 appears to be a bank of clouds. They compare 
 this map with a paper one in front of them. The 
 penciled straight line joining their starting-point 
 and their destination passes through a character- 
 istic bend in the first river and just to the east of 
 the junction of a minor tributary and the second 
 large river. A touch of the rudder and the craft 
 is brought over this same line on the earth-map 
 below them. For a time they will steer their 
 course toward this point on the second river forty 
 
142 THE BOOK OF THE SKY 
 
 miles to the north of them. Looking downward 
 one of them makes a note of the drift of the craft 
 in the wind; he corrects for this and notes the 
 resultant position of the compass which is to be 
 maintained unless the direction of the wind 
 changes. 
 
 Below them nearly two miles are the peaceful 
 farms. The streams and rivers are fringed with 
 a filigree of dark green foliage. A variety of 
 yellows and browns of ripening crops and a mul- 
 titude of greens of patches of woods, waste, and 
 meadow, all dulled to deep shades by an infinite 
 number of shadows, spread for miles ahead and 
 to the left of them, melted into the sky by the 
 sunlit faint bluish haze. To the right fifty miles 
 away lies the bay which meets the ocean at the 
 cape. Beyond shimmers the ocean in the early 
 morning sunlight and its horizon is faintly visible 
 one hundred and twenty miles away. Alone in 
 space they are conscious of their insignificance. 
 Those small dots in the fields below are men at 
 work, and it seems strange that men should be 
 engaged in earthly labors while they are abroad 
 on wings. Earthly duties seem far away from 
 this dreamland. The feeling of insignificance 
 gives way to one of independence. A touch of 
 the controls and the craft responds. Mastery of 
 the air! What a superb feeling! 
 
 The craft bores onward into the north. They 
 pass villages and to\Fns of straggling insignifi- 
 cance. They do not care even to learn their names 
 
ANNffllLATING DISTANCE 143 
 
 because towns are not landmarks for this mode 
 of travel except for short distances and low alti- 
 tudes. Large rivers are their signposts. There 
 are no clouds about them so the time is spent 
 chiefly in viewing the landscape far below. A 
 thread-like line to the right is a railroad and that 
 slightly bulging splice in the thread is really a 
 limited train. It appears like a jointed worm and, 
 by looking closely, it is seen to be moving along 
 its thread. Yes, it is crawling on schedule uncon- 
 scious of the speck in the sky which is annihilat- 
 ing distance. 
 
 The earth is a varied pattern of very dark 
 shades. The patches of woods are extremely dark 
 green shades — ^about as dark as the top of yonder 
 gas-tank which has been freshly painted black. A 
 leaf on a tree may be fairly bright compared 
 with a black cloth when viewed side by side, but 
 the condition in the woods is different. Many of 
 the leaves are receiving full sunlight but inter- 
 spersed among the highlights are numberless deep 
 shadows. The combined effect as seen from the 
 heights above is a very dark shade just as if all 
 the greens were mixed or greatly subdued with 
 black pigment. The same is true of fields and 
 meadow, for here are the numberless shadows on 
 a miniature scale compared with the woods. 
 
 The meadows, swamps, and fields of growing 
 crops are not as dark as wooded patches but they 
 are very dark. Their colors vary on this sunlit 
 summer's morning from shades of blue-green and 
 
144 THE BOOK OF THE SKY 
 
 various greens to the yellows and browns of 
 ripening crops. The first large river is now passing 
 below. It is a brownish color near the shore where 
 the mud or sand bottom is adding its color to that 
 of the reflected blue sky and of the natural blue- 
 green color of water. This brownish color gradu- 
 ally changes to yellowish green as the distance 
 from the shore increases untU the color becomes 
 a blue-green in the deep water hundreds of feet 
 from either shore. The airmen recall that, de- 
 spite the dark shade of the water, it is still twice 
 as bright as the deep ocean water when viewed 
 vertically many miles from shore under the same 
 conditions. Most of its brightness as viewed ver- 
 tically is due to light diffused within it, as is well 
 known to the observant airman who has often 
 noted the shadows of clouds cast upon water on 
 a simny day. Water varies greatly in color and 
 brightness as viewed from cloudland. 
 
 Now a black spot resembling a pool of ink is 
 drifting beneath. It is a small quiet lake of clear 
 unruffled water. The clear deep water and porous 
 bottom of feathery sUt reflect practically no light. 
 The surface, as a mirror, reflects an image of the 
 zenith sky vertically upward but this image is 
 only two per cent as bright as the sky itself. Thus 
 little light comes back toward the airmen from 
 this pool, hence it appears almost black. But this 
 is the airman's mirror. On passing vertically 
 over a quiet little lake the airman is able to see 
 his tiny image reflected by the surface. This 
 
ANNlHrLATING DISTANCE 145 
 
 gives him a true vertical which, is difficult to obtain 
 with certainty by instruments in an airplane 
 owing to the inconstancy of the speed and the 
 unsteadiness of the craft. At this altitude the 
 airmen could hardly find their image because it 
 would be like looking for an airplane at twice 
 their distance from the earth; however, it is read- 
 ily seen at altitudes up to a mUe or so. 
 
 One of the surprises of the air is the dullness 
 of the coloring of the earth's areas; that is, the 
 deep shades which greet the eye. A striking ex- 
 ample is met in autumn when the woods are ablaze 
 with a riot of color. From the heights above, this 
 dulls to a dark shade of buff or brown owing to 
 the admixture of the excessive amounts of black 
 in the shadows. Viewed closely the individual 
 leaves are seen and the shadows are ignored. 
 This is the general reason why the brilliant colors 
 of Nature dull to tertiaries when viewed from the 
 air, but, of course, the low-lying earth haze is 
 also more or less influential in this direction. 
 
 The details of the landscape are varying con- 
 tinually and their contemplation is enjoyable and 
 restful. The unfolding of the earthly map as a 
 whole is magnificent and as each river comes into 
 view in the distance, one feels a gentle thrill. 
 Bright streaks here and there indicate the works 
 of man. These highways are the brightest objects 
 in the landscape except the sunlit sides of light- 
 colored buildings. Straight lines and symmetry 
 characterize man's works but Nature is devious, 
 
146 THE BOOK OF THE SKY 
 
 more poetical. Symbolic of this is the stream 
 below. It empties yonder into the larger river 
 at a point oiiLy a few miles from its source and 
 its entire course is plainly visible. Its source lies 
 in yonder patch of wooded waste and wanders 
 apparently aimlessly, looping back here and there. 
 It travels far to go a short distance, but does not 
 this stream hold forth a lesson? It is not neces- 
 sarily aimless ; instead, as it journeys to a certain 
 destiny, it is interested in going, not merely in 
 arriving. Elvers and streamlets may symbolize 
 this lesson to aerial mankind. Man may realize 
 his aims even though he dares to be interested in 
 going as well as in getting there. The two airmen 
 will arrive at their destination happier, fuller 
 men by being interested alrag the way. The 
 poetry of life is along the v ij^kad it need not 
 interfere with progress. To see and to admire 
 the sunset on the way need neither to make man 
 late for dinner nor to defer his progress to- 
 morrow. 
 
 As the airmen watch the details of the earthly 
 map slip by and philosophize regarding Nature 
 and her ways on this clear summer's morning, the 
 cloud-bank early suspected of lying to the north 
 gradually reveals itself. At this point they are 
 approaching it so rapidly at a mile or so above 
 its level that, apparently, it is drawing like a cur- 
 tain over the earthly map ahead of them. They 
 drop down at a rapid glide and soon are below 
 its level. Here they quickly sight the particular 
 
ANNIHIIATmG DISTANCE 147 
 
 bend in the third river which is intersected by the 
 penciled line on their map before them. Noting 
 the drift and the compass after pointing the craft 
 toward this new objective, they give immediate 
 consideration to the cloud-bank. Shall they go 
 above or below it? Their knowledge of clouds 
 and their relation to the weather makes it easy to 
 decide and happily they conclude that they will 
 go above the clouds. Below the clouds it would 
 be dull and dreary; above them lies the blue- 
 canopied fairyland. They rise at an angle which 
 will take them over the rapidly approaching 
 leaders of the pack. As the craft sails over the 
 leaders it "bumps" slightly, for it is not uncom- 
 mon to find eddies or local air-currents in the 
 immediate neighborhood of isolated clouds. 
 
 Soon they are above the vast white vaporous 
 sea and steadily they climb. If they continued 
 their course below this stratum of clouds they 
 might possibly encounter rain or fog eventually. 
 Up above in the sunlight they avoid this possi- 
 bility and the compass will take them approxi- 
 mately straight toward their destination. If the 
 wind at their altitude should change in direction 
 they could detect approximately the new drift by 
 sighting upon the slowly drifting clouds below 
 them. They are now on an uncharted sea but their 
 compass and their knowledge of the ways of the 
 air are reliable. There only remains a possibility 
 of trouble if the layers of clouds should remain 
 ttnbroken for the next hour when they should be 
 
148 THE BOOK OP THE SKY 
 
 near their destination. It is not joyful to con- 
 template going down through, that layer of clouds 
 ■whose thickness can only be judged from above 
 by their knowledge of clouds, Kut there is only 
 a remote possibility that the sky at their desti- 
 nation will be overcast because the weather bureau 
 announced upon inquiry before they started their 
 journey that clear weather prevailed this morn- 
 ing throughout the region toward which they are 
 traveling. 
 
 The delights of traveling again in cloudland 
 are sufficient compensation for the scanty risks. 
 They enjoy the serene blue of the heavens and the 
 calm snow-white ocean below them. They watch 
 their shadow, arrayed in a delicately colored 
 fringe, glide along the surface of the white sea 
 below, keeping pace with them. The minutes pass 
 and the miles are left behind more rapidly than 
 the minutes. In less than a half hour a dark 
 bluish area appears ahead like a lead in an ice- 
 field. The details of earth gradually appear 
 through this dark bluish opening and soon the 
 layer of clouds is left behind. A glance over the 
 earthly map shows them that they have passed 
 beyond their last signpost — a certain bend in a 
 large river. No other prominent landmarks re- 
 main but a careful comparison of the two maps — 
 earth and paper — reveals some small streams, but 
 of more importance, three railroads converging 
 apparently toward the metropolis which is their 
 destination. They check their course and lean 
 
ANNffllLATING DISTANCE 149 
 
 back satisfied. A rough estimate indicates that 
 they should be well -within fifty miles of their 
 objective. At their present altitude — eight thou- 
 sand feet — ^their radius of vision is over one hun- 
 dred miles. Why, then, does not the city appear 
 in the distance? The morning has been slightly 
 hazy but the visibility has been fairly good. The 
 faithful tireless motor continues its roar, revolv- 
 ing a thousand times or more for each mile that 
 it forges ahead — over two hundred thousand 
 revolutions for its two-hundred-mile trip. Each 
 revolution has pulled the craft further ahead than 
 the length of a man's step and it makes nearly 
 two thousand of these "steps" each minute. So 
 far it has not hesitated. How the airmen come 
 to admire the faithfulness of a motor, the uncom- 
 plaining perfect cooperation of many parts, and 
 the trustworthiness of materials of construction! 
 Minutes have passed and they should be within 
 thirty miles of their destination. Could it be that 
 they have miscalculated since the passage of the 
 cloud-bank made it possible again to consult the 
 map? With straining eyes, small ghostly-white 
 shapes are distinguished in the distance. Their 
 straight lines indicate the handiwork of man. 
 Then suddenly a metropolis pops out of the haze 
 — a smudge of its own making. The airmen recall 
 this characteristic of large cities for, while the 
 range of clear vision on such a day may extend 
 for fifty or seventy miles at their present altitude. 
 
150 THE BOOK OF THE SKY 
 
 cities remain hidden in their own smudge until 
 they pop out quite suddenly at close range. 
 
 The remaining miles are rapidly left behind 
 and the city grows apace. The airmen drop 
 gradually to a lower altitude ; soon they are pass- 
 ing over the residential districts. How intermi- 
 nably extensive that city has always appeared 
 w^hen measured by the tedium of street-car rides 
 and by the meters of taxicabs. But here below 
 them lies the entire city, a huddled mass of minia- 
 ture geometrical solids, distributed with more or 
 less order. These regular masses are densely 
 packed in the grayish center of the group — the 
 region of terra cotta buUdings in the modern 
 business district. Then there is a compact red- 
 dish zone of general brick construction and the 
 outlying regions are whitened by the light-colored 
 residences, which decrease in density and end in 
 a scattering at the suburban limits. The whole 
 might have been built by a giant at play with his 
 blocks. 
 
 The airmen tumble out of the sky in joyful 
 antics and, at an elevation of two thousand feet, 
 soar across the business section. What a misno- 
 mer is the term "skyscraper." In one of these 
 miniature buildings they will soon be transacting 
 business. The airmen look for an oval, for the 
 landing-field is a race-track. The mockery of it ! 
 There it lies in the fringe of scattering houses 
 beyond. They search for a smokestack, a bonfire, 
 or even a waving flag to teU them the direction 
 
ANNffllLATING DISTANCE 151 
 
 of the wind. Ascertaining this, they drop down 
 rapidly, head into the wind and fly over the field 
 with eyes alert for its details. With a stiff bank 
 they circle back, and heading into the wind again, 
 they drop gently toward the ground at the lee- 
 ward of the field. The ground rushes upward; 
 the details which were plainly visible at an ele- 
 vation of a hundred feet now become blurred 
 owing to the high speed and their proximity. The 
 motor is throttled and there is the slightest jar 
 as "three points" touch the ground. The motor 
 is unthrottled and the splendid craft is taxied to 
 the border of the oval. 
 
 The airmen emerge from their cockpits, and 
 alight somewhat stiffly. Are they here in reality, 
 or are they in dreamland? The hour is nine 
 o'clock; business hours have just begun; two 
 hours ago they were at the other side of the state. 
 Have they really soared two hundred miles 
 through the air since breakfast on this glorious 
 morning? Everything points toward reality. As 
 they walk away their gaze lingers caressingly 
 upon that faithful tireless craft, and there is 
 framed in their minds words of grateful admira- 
 tion for this dream-like heritage of the efforts of 
 brave and learned men who pioneered in the 
 science of flying but who did not live to feel the 
 superb thrills of the mastery of the air. These 
 men and all mankind are obligated more fully to 
 science each hour of the day. 
 
CHAPTER XV 
 
 A PHILOSOPHY FOE FLYING 
 
 "Did man compute 
 Existence by enjoyment, and count o'er 
 Such hours 'gainst years of life, say, would he name 
 threescore? 
 
 — ^Bykon. 
 
 TT is not the aim to present a phUosophy for 
 -■- air-travel to be adopted universally by persons 
 possessing widely different temperaments but to 
 air a conviction tbat, in order to extract the most 
 from air-travel, a satisfying philosophy is neces- 
 sary. Furthermore, it should be stated at the 
 outset that this discussion should not be miscon- 
 strued as indicating that flying today is fraught 
 with dangers. On the contrary, there is much evi- 
 dence, statistical and otherwise, to prove that 
 air-travel is already fairly free from danger. But 
 the air is a new world to mankind in so far as 
 personal invasion is concerned and due to the 
 novelty and strangeness of soaring in cloudland, 
 man experiences a variety of vivid emotions per- 
 haps not unlike those of the backwoodsman who 
 takes his first ride in an automobile through the 
 
 152 
 
A PHILOSOPHY FOR FLYING 153 
 
 congested traffic of a city. The philosophy 
 touched upon here may be faulty and open to 
 many criticisms, theologically, psychologically, or 
 otherwise. It may be unsuited to others in many 
 ways but if it aids an individual, he should cling 
 to it. If it puts him at ease, he is in possession 
 of something which will mark him as a cool one 
 and upon which he will realize large returns for 
 every hour in the air. It will aid him in enjoying 
 to the uttermost not only the beauties of the fairy- 
 land of the clouds, the wonders of Nature's spec- 
 tacles, and the magnificent panoramas, but the 
 many other thrills of flying. It will permit him to 
 extract something — almpst enjoy — those rare mo- 
 ments when disaster seems inevitable. In fact, 
 a satisfying philosophy, through the calmness 
 which it inspires, will sometimes circumvent the 
 grasping hand of Doom. 
 
 A philosophy built upon logic or constructed by 
 means of the facts attending a situation appears 
 to have been uncommon among our soldiers and 
 aviators during the recent war. Perhaps rela- 
 tively few recognized or seriously considered the 
 advantages of meeting the dangers with a mind 
 satisfied by a philosophy built upon facts or logic 
 which would not fail at the crucial point. This 
 does not mean that they did not meet the dangers 
 with determination and brave hearts. It means 
 merely to imply that little has come to light to 
 indicate that sound well-built philosophy pre- 
 yailed. And why should such a philosophy pre- 
 
154 THE BOOK OF THE SKY 
 
 vail? Where in the schools, colleges, or churches 
 are men taught the art of living? That living 
 involves intensity as well as time? That the full- 
 ness of living depends upon the individual? A 
 painting, a sunset, and life are similar in that 
 man extracts from each that which he puts into 
 each, but in compounded form. Life derives its 
 value from use alone. 
 
 It seems that the philosophy of life should be 
 presented somewhere during the schooling of 
 young men and women. In the absence of this, 
 when the nation was forced to make an army 
 quickly, would it not have been a valuable part of 
 the training of soldiers? It seems that it was 
 preferred that the men give little thought to that 
 which lay behind the curtain of the future. But 
 this is like attempting to stem the tide of eternity, 
 for minds will think, notwithstanding efforts to' 
 control them, in search of a philosophy which will 
 satisfy. It seems certain that this thinking is not 
 directed logically by the majority of individuals. 
 It is as easy to believe that schools are unneces- 
 sary and that each person may educate himself 
 as it is to conceive that each, unaided, may evolve 
 a satisfactory philosophy or attitude toward life. 
 Contemplation under the stress of danger has 
 made many involuntary cowards. It has under- 
 mined morale with the result that many have 
 failed in the emergency although their hearts were 
 brave and true. If man cannot escape his own 
 thoughts, is it not best for him to think out, with 
 
A PHILOSOPHY FOR FLYING 155 
 
 the aid of others if necessary, a satisfying phi- 
 losophy, once for all? 
 
 This psychological aspect of warfare and of 
 other activities fraught with real and imaginary 
 dangers is a subject worthy of extensive treat- 
 ment, but it is not the intention to discuss it at 
 length. It is a subject for qualified psychologists 
 and doubtless there would be many disagreements 
 among them. It is mentioned here because 
 through actual experience or through that of a 
 close friend or relative, many persons realize the 
 importance of mental attitude in the presence of 
 danger or death. Apparently one philosophy 
 found among our soldiers was fatalism. "When 
 my time comes, I'm through" seemed to satisfy 
 many, but is this sound enough to be satisfying 
 in the real critical moments? Others seemed to 
 •believe that a certain shell or bullet would have 
 their number on it but doubtless relied with a 
 weak assurance upon its being lost by the wayside 
 during its devious journey to the battle-front. 
 Doubtless some of these further reduced their 
 chances of meeting it by contending that it might 
 be sent across when they were on leave far behind 
 the lines. But were these flimsy philosophies sat- 
 isfactory in the crucial moments? There is no 
 evidence that those men did not meet their dan- 
 gers bravely, but who knows with how much inner 
 anguish? Who knows how much intensity of 
 living was ignored or lost during those days of 
 mental stress? A sound philosophy would be 
 
156 THE BOOK OF THE SKY 
 
 worth much to every soldier, even though it did no 
 more for him than to eliminate the torture of an 
 unsettled mind. 
 
 One day two aviators plunged to earth at a 
 training field and were Mlled before the eyes of 
 a number of their associates. Two of the latter 
 were just seating themselves in their craft when 
 they witnessed the fatal plunge, the outcome of 
 which they could predict before their eyes had 
 followed it all the way to the inevitable crash of 
 doom. One of them turned to the other and stated 
 without the slightest tinge of selfishness, "That's 
 another accident out of our way." Doubtless by 
 some process of intentionally careless reasoning 
 he made himself believe that his chances improved 
 each time an accident occurred — to somebody else. 
 Such an argument did not spring from selfishness 
 for he was a splendid fellow, but he was willing 
 to leave to Fate the distribution of her supply of 
 accidents. 
 
 The best that can be said of these philosophies 
 is that there is little sound reasoning behind them 
 and that they are not based upon proved facts. 
 In other words, they are at best unphilosophical. 
 One may banter with himself along the ordinary 
 ripples of life but it is difficult to believe that he 
 will approach the white rapids or roaring cata- 
 ract calmly with the same joking careless philos- 
 ophy. It may be that such philosophies as those 
 mentioned would satisfy a large class of persons 
 among whom superstition still lurks and logical 
 
A PHILOSOPHY FOR FLYING 157 
 
 thinking is a novelty. If so, it would be wrong 
 to undermine tliem without providing a satisfac- 
 tory substitute; therefore, they are not to be con- 
 demned. 
 
 The attainment of mental ease or of a self-sat- 
 isfying attitude toward life is such a personal 
 matter that many prescriptions may be necessary. 
 It is with some misgivings that this brief discus- 
 sion is included in this little volume because a 
 thorough discussion is unwarranted and even 
 these few pages may appear to be a digression 
 from the main theme. However, the question o'f 
 fear arises very generally from those who have 
 not yet enjoyed the delights of flying. Further- 
 more, fear and lack of a definite philosophy have 
 robbedmany of those who have invaded cloudland, 
 of much of the joy that waited upon them. Fly- 
 ing is such a new possibility and the results of 
 falling, for instance, are so easily visualized that 
 most persons today think of flying as an activity 
 only for dare-devils and for those who care not 
 how long they live. The evolution of flying dur- 
 ing the stress of war gave this activity the ap- 
 pearance of being extremely hazardous. In the 
 hope of aiding to set flying aright in the popular 
 mind this brief chapter is included. In what fol- 
 lows will be found the rudiments or steps which 
 have satisfied some and helped others who desired 
 a philosophy of flying which was based upon a 
 logical array of facts or reasonable arguments. 
 There are many statistical facts available per- 
 
158 THE BOOK OF THE SKY 
 
 taining to aviation accidents. The statistics will 
 not be quoted here because they will be super- 
 seded as the years pass by still more favorable 
 ones. During the stress of war ia which haste, in- 
 experience, and crowded training fields took their 
 toll, there was only one fatality for thousands 
 of flying-hours. At some of the advanced fields 
 few fatalities have resulted during their entire 
 existence. At some of these, many thousand 
 flying-hours were accumulated per fatality. Sit- 
 ting down before these statistical facts and con- 
 servatively eliminating those due to haste, unsat- 
 isfactory equipment, congested conditions, and 
 intensive training, the ratio of fatalities and seri- 
 ous accidents to total flying-hours dwindles enor- 
 mously. There is still another item to be consid- 
 ered, namely, accidents for which the aviator 
 himself is solely responsible. Inasmuch as these 
 constitute a large percentage of the total of acci- 
 dents, when they are eliminated, those chargeable 
 solely to aircraft dwindle to insignificance. In 
 fact, the final figures are such that an individual 
 may, on the average, live to a ripe old age and 
 still have spent as many flying-hours in the air 
 as he could possibly desire for ordinary recrea- 
 tional and business purposes. This, then, is one 
 of the first steps in building a philosophy. 
 
 In the last few years the design and construc- 
 tion of aircraft have progressed remarkably. If 
 desired, an airplane may be designed for high 
 inherent stability so that its control approaches 
 
A PHILOSOPHY FOR FLYING 159 
 
 the ease of driving an automobile. It is reason- 
 able to expect continual improvement for some 
 time to come. From such deductions one becomes 
 satisfied as to the dependability of aircraft and 
 the safety of flying. 
 
 Then to philosophize further, one may find it 
 possible to convince himself that living is a prod- 
 uct of time multiplied hy intensity; in other 
 words, that living is not measured in terms of 
 duration. One person may live a whole lifetime 
 with unobservant eyes and unresponsive sensi- 
 bility and still not accumulate as much living as 
 another who drinks of the joys of life as he passes 
 along a brief interval. From this viewpoint it is 
 essential to compare the beauties, thriUs, won- 
 ders, inspirations, and emotions in the aerial 
 world with those of the more prosaic worlds with 
 which mankind is familiar. There can be no 
 ennui for mankind in cloudland for a long time 
 to come. 
 
 After a person has become satisfied that flying 
 is not dangerous, let him have his first flight with 
 open eyes and alert sensibility, during which, 
 among other things, he will be thrilled with this 
 superb triumph over Nature. He will enjoy the 
 grandeur of the extensive range of vision at high 
 altitudes incomparable with those from earthly 
 viewpoints. On the next flight he may be dis- 
 tracted from contemplation of the earth's distance 
 and hardness by some overwhelmingly beautiful 
 cloudscapes. He may wander in an out at will 
 
160 THE BOOK OF THE SKY 
 
 among the brilliant white vaporous marvels of 
 fairyland xmtil he cannot believe that anything 
 as drab and smudgy as the earth can exist in the 
 universe. He may begin to appreciate the mar- 
 vels that the airplane has brought almost to his 
 door. Then let him taste the delights of cross- 
 country flying and his imagination will begin to 
 aid him in appraising this latest triumph of man- 
 kind. Finally, treat him to a series of stunts by 
 way of emphasizing the fact that mankind is 
 master of the air. In this wild abandon wherein 
 the craft simulates the freedom of a bird, the 
 candidate becomes ready to consider the philos- 
 ophy that living is the product of time multiplied 
 by intensity. 
 
 The wingless individual in the two-dimensional 
 world at the earth's surface must live years to 
 overtake his contemporary who has spent these 
 glorious intense hours in the air. The searcher 
 after a philosophy for the air may now be willing 
 to admit that in the few hours in the air he has 
 lived as much as though he had spent his allotted 
 lifetime in the less intense living on earth. He 
 may now agree that living "is measured by heart- 
 throbs" and that "it matters not how long we 
 live, but how." He may now calmly contemplate 
 the possible dangers of flying with the thought 
 that he has lived his lifetime and that he will 
 leave the matter of heaping measure to Fate. If 
 the aerial world does not hold forth for him hours 
 crowded with the joy of living he cannot be sat- 
 
A PHILOSOPHY FOR FLYING 161 
 
 isfied in tMs life, and therefore, should not con- 
 template with terror the extreme result of an 
 aerial accident. He might logically even look 
 forward with pleasure to his entrance into an- 
 other life which may possibly hold a satisfying 
 fullness for him. Either way he may philoso- 
 phize pertaining to the fullness of living in the 
 aerial world should logically prepare him for 
 calmly contemplating that world which lies be- 
 hind the veil of mystery. 
 
CHAPTER XVI 
 
 [AERIAL ANTICS 
 
 "One crowded 'hour of glorious life 
 Is worth an age without a name." 
 
 — Scott. 
 
 THE traveler in cloudland encounters so many 
 new experiences that sometimes he even may 
 doubt the reality of the whole. If he is given to 
 serious thinking he may find himself attempting 
 to appraise aviation in respect to the happiness 
 and progress of mankind. His appraisal, how- 
 ever, is enlarged with each new experience until 
 he is certain that, at least, he cannot overestimate 
 its influence upon the future of civilization. He 
 may marvel at the past accomplishments of air- 
 craft and dream of those to come, but complete 
 mastery of the air does not become a vivid reality 
 until he has sported in space with the wild aban- 
 don of the care-free bird. To the aerial traveler 
 clouds have been beautiful; the extensive ranges 
 of vision from the heights of cloudland have been 
 wonderful; storms as seen from above have been 
 awesome. All have been interesting and inspir- 
 ing; some have been thrilling; but the superb 
 
 162 
 
AERIAL ANTICS 163 
 
 thrills await those who have not been through a 
 series of aerial antics. 
 
 It is commonly observed, "How gracefully an 
 airplane performs stunts but how dangerous they 
 must be." As a matter of fact, such a craft is so 
 ponderous and presents such resistance to motion 
 that grace is a natural result. At sufficient alti- 
 tudes the so-called stunts are not dangerous when 
 the craft has been constructed with a proper fac- 
 tor of safety. Of course, the strains on certain 
 parts of the craft during these antics are greater 
 than in straight flying but these minor risks may 
 be ignored. At least, they may be compensated 
 by the superb thrills of aerial triumph. 
 
 Those whose experience with airplanes is 
 limited to viewing them from the earth generally 
 are impressed with their bird-like movements. 
 Naturally airplanes have assumed the appearance 
 of birds somewhat, because the bird was devel- 
 oped and equipped for flying. If there were 
 available more efficient or practicable principles 
 of flying, doubtless Nature would have developed 
 them in some flying animal. The differences 
 between the appearance of a bird and an airplane 
 are those due, in general, to mechanical consid- 
 erations of the present time. 
 
 After experience with airplanes has been gained 
 in the air, the bird analogy is likely to prove 
 inadequate despite the bird-like appearance of the 
 craft. Straight flying, volplaning, and some of 
 the milder stunts are strikingly similar to the 
 
164 THE BOOK OF THE SKY 
 
 movements of a flying bird but many of the ma- 
 neuvers possible in airplanes are not approached 
 by Nature's flyers. 
 
 The utmost freedom of an airplane strongly 
 impresses one when in the air. Furthermore, on 
 looking down into the depths of air, somewhat 
 visible owing to the luminous haze, and viewing 
 airplanes far below and on all sides, one is likely 
 to be further impressed with the fact that, after 
 all, the air is fluid. By some such process of 
 analysis and through certain obvious associations, 
 it becomes easy to liken the airplane to a fish free 
 to swim in any direction in its element. To the 
 author the bird analogy is inadequate and the fish 
 analogy has been drawn upon to supplement the 
 deficiencies of the former. This may appear to 
 be a minor point but it is important in awakening 
 the imagination to the possibilities of flying and 
 in aiding in visualizing the details of some of the 
 most startling aerial antics. 
 
 An airplane may be controlled in all three 
 planes separately or in combination. If these 
 three controls and the three degrees of freedom 
 are carefully yisualized, it is not difificidt to de- 
 termine how some of the more simple stunts are 
 carried out. It would be tedious to read the de- 
 tails of the various definite stunts and it is almost 
 hopeless to attempt to describe in words the vast 
 variety of combinations which would comprise an 
 hour of aerial antics. Words are inadequate to 
 describe the thrills and emotions of the first 
 
AERIAL ANTICS 165 
 
 experience with this phase of flying, but, perhaps, 
 with the aid of his imagination the reader may 
 gain an idea of what one sees, feels, and thinks. 
 
 Perhaps a question might arise as to the advis- 
 ability of running even the minor risks of stunt- 
 ing. The answers which appear most appropriate 
 are to the effect that into the first half-hour of 
 aerial antics, owing to the intensity of living, the 
 fullness of a year on earth may be crowded and 
 that stunting appears to be one of the most nat- 
 ural play-spells for the airman. Aerial antics 
 serve the purpose of a safety valve for the nerv- 
 ous tension which is incident to the novelty of 
 flying. "When one feels himself growing tense, 
 a few minutes of the careless freedom of these 
 antics makes him a complete master of the air 
 again. 
 
 Let us assume that an aerial passenger is on 
 his way aloft to be treated to a series of stunts. 
 When the craft reaches an altitude of two or 
 three thousand feet many of the stunts may be 
 done with safety, but inasmuch as nearly every 
 stunt results in the loss of altitude the pilot climbs 
 steadily upward. The passenger wonders all this 
 time when things will begin to happen. The 
 minutes lengthen as the altimeter indicates higher 
 and higher altitudes. Ten thousand feet is 
 reached and still the craft climbs upward. Sud- 
 denly it tilts downward at a fair angle and gains 
 speed. The passenger catches his breath and 
 awaits in suspense with his senses alert. The 
 
166 THE BOOK OF THE SKY 
 
 pilot pulls back the joystick, lifting the elevators, 
 and the craft goes into a loop. The centrifugal 
 force is very great as the craft describes the loop. 
 The passenger feels as if an invisible mighty 
 hand is forcing him into his seat. If he were 
 seated upon a spring weighing apparatus, he 
 would be startled by the fact that he now weighs 
 hundreds of pounds. He attempts to raise his 
 hand but it does not respond. The muscular 
 force which he ordinarily exerts is insufficient to 
 lift it. He tries again, exerting greater force and 
 the hand rises, but how unnaturally heavy it is! 
 It takes much of the power of his arm to raise it. 
 During this time the earth wobbles grotesquely 
 describing a somersault, and then settles to its 
 proper place again. The pilot turns around with 
 a grin showing amid the inexpressive leather and 
 goggles of the rest of his countenance. The pas- 
 senger has looped the loop but he did not recog- 
 nize it, for in this first experience the earth did 
 the somersault while the passenger was mystified 
 by many unrealities. 
 
 The course of the craft is now bent slightly 
 downward but not such a high speed is attained 
 as before. Suddenly the craft is turned upward 
 into a lazy loop. As it reaches the top of the 
 loop its centrifugal force is almost spent and the 
 passenger feels that the powers are uncertain in 
 their purpose. The centrifugal force which would 
 pull him upward vies with the gravitational force 
 of the earth which would pull him downward. He 
 
AERIAL ANTICS 167 
 
 hovers in space now touching the seat, now gently 
 hanging by his belt. With head downward he 
 views the distant earth. The craft goes on over, 
 finishing the loop slowly and he notes that this 
 time he has looped and the earth has merely 
 wobbled. After a few loops he becomes accus- 
 tomed to the unnatural positions and is able to 
 describe a loop while the earth remains quite 
 stationary. This is one of the simplest and most 
 natural antics of the air. 
 
 The craft roars onward on full throttle with the 
 passenger wondering what is going on under- 
 neath that leather helmet in front of him. Sud- 
 denly they shoot upward at a steep angle and the 
 roar of the motor dies down. The craft seems to 
 become stationary; the passenger weighs nothing, 
 at least he does not seem to be sitting with any 
 weight upon the seat. Then the craft drifts back- 
 ward and downward as if attempting to leave 
 him. A series of these "stalls" come in succes- 
 sion and add thrills. 
 
 With throttle wide open the motor roars onward 
 again as the craft maintains its altitude. Appar- 
 ently this lull is necessary as the pilot thinks up 
 some more devilishness. Suddenly the craft 
 shoots upward as if to do a loop, then, cat-like, it 
 squirms over right-side-up but headed in the direc- 
 tion whence it came. The passenger is in a 
 muddle, for first the earth's surface stood on end 
 and then seemed to whirl on its center for one 
 revolution. He will pass through many "Immel- 
 
168 THE BOOK OP THE SKY 
 
 man turns" and its close relations before he is 
 able to keep the earth stationary in its normal 
 position. 
 
 The airplane continues to tear through space 
 and suddenly the earth's disk seems to be describ- 
 ing revolutions about the axis of the craft. An ob- 
 server in another airplane would see the craft 
 spinning on its axis as it bored through the air 
 horizontally, or nearly so. The passenger is in a 
 hopeless muddle, for he has no idea of what is 
 going on. From pre-arranged signals the pilot 
 has informed him that they were to do a "barrel 
 roll, ' ' and they did. 
 
 Thus the passenger is treated to a variety of 
 stunts. Seldom could he recognize the particular 
 stunt the first time he experienced it but, usually, 
 after several successive ocurrences, he is able to 
 note the details as he is passing through it. 
 
 Such antics as "dead bird" and "falling leaf" 
 are to him at first just a confusion of somersaults, 
 revolutions, and wobbles by both himself and the 
 earth without any coordination. They were wildly 
 thrilling, even awesome, but he experienced little 
 fear because of the satisfaction of knowing that a 
 sane person was in front of him who was sharing 
 the same risks, knowingly and willfully. 
 
 During these acrobatics they have lost several 
 thousand feet of altitude and it is time to begin the 
 tailspin which the pilot has in mind. The craft 
 suddenly leaves its horizontal direction and rises 
 to a stall, but instead of slipping backward at the 
 
AERIAL ANTICS 169 
 
 high point, it starts to topple over at a steep angle 
 witli nose downward. As it reaches the highest 
 poiat of its upward spurt the motor dies down and 
 the craft remains seemingly stationary in the air. 
 The passenger looks around and there slanting up- 
 ward steeply from him is the left wing gracefully 
 describing an arc as the craft begins to topple 
 slowly into a nose-dive. Here is a superb moment 
 in the air. It really is a matter of a few seconds 
 which seem like minutes, maybe hours, for al- 
 though the airplane shortens distance it certainly 
 lengthens time. The passenger looks down upon 
 the intricate pattern of a city. He wonders how 
 mankind can be really interested in such trivial 
 earthly activities as are indicated by the patterns 
 below him. He tries to comprehend the depths of 
 lethargy which make man content to work out 
 those silly pavement patterns in the miniature city 
 park below. He pities those earth beings who live 
 in the drab dullness beneath that smudge of haze. 
 For a moment his glance sweeps the horizon 
 across large bodies of water and thousands of 
 square miles of the earth's surface and he asks 
 himself for the hundredth time, "Is this reality?" 
 In these few seconds the craft has slowly 
 toppled over "until it has assumed the position of a 
 huge bird ready to swoop downward upon its prey, 
 then the pilot puts it into a tailspin. The earth be- 
 comes a whirling blur. The whir of the wires and 
 struts overpowers the noise of the weakened ex- 
 haust of the throttled motor. The whirling con- 
 
170 THE BOOK OF THE SKY 
 
 tinues and the passenger becomes aware of a sen- 
 sation of dizziness mingled with conflicting emo- 
 tions, as well as thoughts akin to those of the poor 
 sailor on a rough sea. WhUe the craft was slowly 
 and ponderously toppling over he noticed with a 
 flicker of a grim smile, a huge cemetery far below 
 him, its white dots in striking alignment. He re- 
 called with a chuckle the Salvation Army sign 
 which he passed this morning with its timely ad- 
 vice, "Prepare to meet thy God." 
 
 As the craft spins downward he finds with the 
 increasing nausea that his interest in life is wan- 
 ing. He has passed through many superb mo- 
 ments but the tailspin. itself, depite the supreme 
 moments at its beginning, is not so attractive be- 
 cause it makes him dizzy. But the pilot in glee 
 looks upward with a fiendish grin as the hundreds 
 of vertical feet speed by. The details of the 
 earth's surface are rapidly growing larger. A 
 few clouds at five thousand feet are rushing 
 up toward them. They are heading vertically 
 downward into one. There is a moment of 
 white blindness and they have passed through 
 it but the pilot is no longer grinning. His 
 head is bent and his shoulder is working. The 
 passenger notes the dead propeller, and the 
 cemetery beyond in the same glance, and even 
 connected in his thought. The craft stops spin- 
 ning and goes into a straight nose-dive. The 
 pilot has pumped up the pressure on the "gas" 
 and is now trusting to a rapid vertical dive for 
 
AERIAL ANTICS 171 
 
 sufficient air-resistance to turn tlie propeller over 
 and to start the motor. Seconds ago they emerged 
 from the cloud at an altitude of four thousand 
 feet. The altimeter now reads three thousand and 
 still they are diving straight toward the earth. 
 How hard and foreboding it appears ! The pas- 
 senger's philosophy makes it possible to view the 
 outcome fairly cahnly. He even exchanges a grin 
 with the pilot who looks upward as if to gain some 
 devilish pleasure, if nothing else, should a hurried 
 landing be necessary. The altimeter registers two 
 thousand feet, dangerously low at the speed of 
 their nose-dive. The pilot is about to pull the 
 craft out of the dive and attempt a landing when 
 the propeller moves, then it moves again! In a 
 long second or two it has described a half revolu- 
 tion. The exhaust begins to pop, then to roar as 
 the engine picks up. The pUot pulls the diving 
 craft through a huge arc into a horizontal position 
 a few hundred feet from the ground. Then with 
 the controls set for an easy climb he looks back and 
 expresses his feeKngs to the passenger in the sign 
 language of cloudland. 
 
 Possibly those who have not experienced the 
 reality may be able to obtain some idea of what 
 one sees, feels, and thinks during such wild antics. 
 The foregoing is a typical series. During the 
 training of aerial gunners, "machine-gun cam- 
 eras" were used to some extent. The aerial gun- 
 ner pursued another craft which tried to evade it, 
 or perhaps two aerial gunners would have a duel 
 
172 THE BOOK OF THE SKY 
 
 in the air. Such activities called for daring and 
 skill in gunnery and maneuvering. It is here that 
 aerial antics display their usefulness, and one may 
 enjoy them the more when there is a utilitarian 
 purpose behind them. It seems that aerial "cam- 
 era" gunnery, in which pictures are taken instead 
 of bullets dispatched, might supply one of the fu- 
 ture sports or aerial contests because it would 
 measure skill and courage. The photographic 
 records could be adjudged according to definite 
 rules and thus the champion aerial duelist could 
 be determined. 
 
 The passenger and pilot are steadily gaining 
 altitude. If they could only meet an airman 
 equipped with a ' ' camera gun ' ' and play * * enemy ' ' 
 for him, the passenger's experiences with aerial 
 antics would be well-rounded out. In the excite- 
 ment of contest he would forget consequences and 
 perhaps find himself on his feet, popping away 
 with his pocket camera as his craft slipped, dived, 
 looped, and climbed. As the aerial gunner 
 swooped around him in wide circles and steep 
 banks, he would gain an idea of the terrific speed 
 of his craft because he now has an object close at 
 hand which makes it possible to appreciate speed. 
 Many in the recent past have enjoyed these superb 
 aerial contests during training for war, but will 
 they be perpetuated as a sport of the air? 
 
 In lieu of an imitation enemy the pilot and pas- 
 senger provide themselves with an imaginary one 
 and the latter gains an idea of fast work in maneu- 
 
AERIAL ANTICS 173 
 
 vering. The antics which he recently experienced 
 one at a time are now compressed or merged into 
 each other. A steep bank, a close spiral, a tailspin, 
 a nose-dive, evolve in" rapid succession, until it 
 appears to the passenger that the pilot's appetite 
 for thrUls is insatiable. During all this time they 
 have neared the ground and just as the passenger 
 becomes convinced of the pilot's suicidal intent, 
 the craft side-slips for a thousand feet or more, 
 rights itself over the field, and dips to a quiet land- 
 ing. 
 
 As the passenger walks away there is a note of 
 sobriety or even of sadness in his expression, for 
 he feels that the superb thrills of his life have been 
 passed. From now on, even the aerial world will 
 not yield thrills equaling those of the past hour 
 of first experiences with aerial antics. In aU the 
 wide scope of man's past, present, or future ac- 
 complishments, his imagination cannot hold forth 
 to him deeper thrills than those of the past hour. 
 But this note of sadness eventually is smothered 
 by the appreciation that the aerial world at least 
 win ever hold in store for him an intensity of liv- 
 ing incomprehensible before today. 
 
CHAPTER XVn 
 
 THE SUPREMACY OF AIE-TRAVEL 
 
 "The best of prophets of the future is the past." 
 
 A LTHOUGH pioneer experiments in tlie prin- 
 ^^ ciples of flight were being carried out in the 
 twilight of the last century, the first practical 
 flights by airplanes were initiated after the dawn 
 of the present century. However, tremendous 
 strides in aviation quickly followed and it is diffi- 
 cult to believe that mankind was gasping ten years 
 ago at flying achievements which in this brief in- 
 terval have dwindled to insignificance compared 
 with the mastery of the air of the present time. 
 Statements of twenty years ago in regard to flying 
 may be read with amusement to-day and they 
 stand as warnings to those who would prognosti- 
 cate the future of aviation. Ten years ago man- 
 kind would have gasped at a world's record flight 
 of fifty continuous miles in as many minutes. To- 
 day the Atlantic Ocean has been spaimed in non- 
 stop flights by airplane and by dirigible balloon, 
 and continuous flights by airplane of several hun- 
 
 174 
 

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THE SUPREMACY OF AIR-TRAVEL 175 
 
 dred miles at one hiindred miles an hour are com- 
 monplace events of daily occurrence. How long 
 will it be before the earth will be encircled in a 
 single flight? 
 
 These statements will be amusing some day, but 
 in order to safeguard them, it may be added that 
 •the marvelous development of flying in the early 
 morning of the twentieth century indicates unerr- 
 ingly that greater achievements in aviation will 
 come rapidly. Although prophecy will be avoided, 
 for it serves no important purpose, the supremacy 
 of aircraft of today is deserving of recognition. 
 
 The intensive experience with aircraft during 
 the past few years has proved their fitness for 
 many activities. Many of the chapters of this 
 little volume are tributes, inadequate though they 
 may be, to the supremacy of air-travel. Aircraft 
 have opened to mankind the delights of cloudland 
 which he could not enjoy otherwise. The mar- 
 velous development of electricity has influenced 
 civilization beyond conception, but the electric 
 motor did not supply something absolutely lack- 
 ing. Power could be had by other means. How- 
 ever, aircraft are essential for invading the aerial 
 world. This, then, is the first mark of supremacy 
 for aircraft, — it brought the delights of cloudland 
 to mankind and opened to civilization the possibili- 
 ties that air-travel may afford. 
 
 Fiction has already utilized the airplane and 
 dirigible balloon for smuggling, blockade-running, 
 and various other spectacular crimes. More than 
 
176 THE BOOK OF THE SKY, 
 
 one character has circumvented the desperate 
 villain by the aerial route. It is said that truth 
 is stranger than fiction, stUl all these events have 
 their parallels already in fact. 
 
 Earthly obstacles do not alter the course of the 
 aerial traveler. His route may be a straight line 
 except for occasional storms and winds. For this 
 reason, aircraft are already supreme for certain 
 journeys. The straight highways of the air re- 
 quire no maintenance and the aerial traveler 
 needs only to consider their signposts — ^barometer, 
 clouds, and winds — ^and look to the speed and en- 
 durance of his craft. MaU service is already out- 
 classing that of the fastest trains over the straight 
 paths of prairie country. Aerial mail service, then, 
 may easily outstrip the past methods of mail car- 
 riage in mountainous countries. In comparison 
 with water-routes the speed and directness of 
 aerial service reign supreme. Mail from interior 
 Africa, for example, may be carried to European 
 countries by aerial routes in a matter of hours in- 
 stead of days as is the case of combined land and 
 water-routes. 
 
 Hurried explorations of densely wooded, 
 swampy, or mountainous countries have already 
 been accomplished. Forest fires have been dis- 
 covered with ease from the air. In the lake-strewn 
 forests of Canada a flying-boat has its landing 
 places ever-waiting. The gliding range of air- 
 craft makes high-altitude flights over such coun- 
 tries fairly safe. For each thousand feet of alti- 
 
THE SUPREMACY OF AIR-TRAVEL 177 
 
 tude an airplane should be able easily to glide a 
 horizontal mile or two. With long-distance dirigi- 
 bles, the passengers need give little thought to 
 landing, and travel over the rough wild countries 
 should be looked upon as quite safe. When the 
 more spectacular flights have been consummated, 
 the aerial traveler still will find a vast world to 
 explore by way of the air. 
 
 As a convenient and rapid means of getting 
 somewhere, the airplane has thoroughly demon- 
 strated its superiority over any other present 
 mode of travel. Flights of two or three hours 
 replace the tedium of railway or steamship trips 
 which consume an entire day or night. As a means 
 for ordinary journeys the past achievements of 
 aircraft surely indicate a great future. There ap- 
 pears to be little danger in prophecy in this respect 
 except that the imagination can not comprehend 
 the possibilities. 
 
 Flying has shown mankind the deficiencies of 
 maps. As the aerial traveler looks down from the 
 heights upon the real map of the earth's surface, 
 and compares it with the one on paper before him, 
 he notes the great variations in most cases. Of 
 course, there are many government maps on which 
 such details as the intricate lacework of coast- 
 lines and the squirming paths of rivers are re- 
 corded with marvelous ability, but the aerial pho- 
 tograph records such details with absolute fidelity. 
 Map-making by means of aerial photography has 
 proved its worth already and there can be no 
 
178 THE BOOK OF THE SKY 
 
 doubt as to tlie supremacy of aircraft in many di- 
 rections in tMs field. 
 
 Already many persons have traveled by air over 
 territory wMcb bas rarely been crossed by any 
 other means of travel. The marvel is that the 
 speed of the aircraft is not cognizant of the topog- 
 raphy of the surface below. Its speed is just as 
 great over the jxmgle as over the rolling prairie. 
 In a few hours and with ease and safety to the 
 travelers, aircraft have made trips which could 
 not be made by other modes of travel in less than 
 days and even months of the greatest hardships. 
 It may aid in visualizing the supremacy of air- 
 travel to describe briefly a flight which illustrates 
 this feature of flying. The flight to be described 
 is commonplace in a certain swampy section of the 
 United States, and portions of it at least, have 
 been made by many persons. Similar examples 
 could be found in various parts of the world. 
 
 Two airmen are donning their helmets as they 
 walk toward their craft. They are about to start 
 on a two-hour flight most of which is over territory 
 which would be considered otherwise inaccessible. 
 Their course will be approximately circular and 
 in two hours they will complete a trip which could 
 not be made without great hardship in less than 
 months by other modes of travel. Still their 
 preparations are merely for a two-hour flight. One 
 can not help noting the extreme simplicity of the 
 preparation for this trip by airplane, compared 
 
THE SUPREMACY OF AIR-TRAVEL 179 
 
 with the outfitting of an expedition to make the 
 trip other-wise. 
 
 They take to the air from a field amid the watery 
 tentacles of a large arm of the ocean. As they 
 gain altitude a beautiful landscape unfolds, for 
 underneath them are inlets, tidal sloughs, and 
 streams, each fringed with the dark green lace of 
 bush or swamp timber. On one side, twenty miles 
 away, is the wide mouth of a large river whose 
 winding course may be traced back easily for fifty 
 miles toward its source. Along its way are many 
 silvery threads leading from it to die away amid 
 the green background. On the other side is the 
 mouth of another large river and its relatively 
 bright path may be followed toward its source in 
 the mountains indistinguishable at the distant 
 horizon. 
 
 As they mount higher other conspicuous details 
 of the landscape appear. These are chiefly rivers 
 and other areas of water. The water-shed of a 
 whole state is visible within their horizon. They 
 now start on their course. Ahead of them is a 
 huge arm of the sea and the coast-line of the ocean 
 is plainly visible thirty miles away. In a few min- 
 utes they are over a body of water which is sev- 
 eral miles wide along their course. As they reach 
 a point over land again they find that they have 
 been off the ground only fifteen minutes. They 
 look down at a certain point and recall that they 
 made a trip from the field to that point by launch 
 not long ago in several hours. The water-route is 
 
180 THE BOOK OF THE SKY 
 
 roundabout and the speed of the launch is slow. 
 Their present route is practically in a straight line 
 and their speed is one hundred miles an hour. 
 
 They head straight onward toward the coast 
 over low land seamed with inlets, streams, tidal 
 sloughs, and swamps. Their altitude is fifteen 
 thousand feet and they may glide twenty or thirty 
 miles in case their motor fails. Ahead of them 
 lies the coast-line mUes away. The horizon of the 
 ocean is barely distinguishable through the haze 
 and they know by their altitude that it is about 
 one hundred fifty miles distant. The brightness 
 of the sky and that of the distant water are so 
 nearly the same that the haze seems to blend sky 
 and ocean. High up in this sky the white sails of 
 a schooner appear to be suspended but it is merely 
 an illusion due to their height. The angular ex- 
 tent of the water between the coast-line and the 
 distant horizon is so much greater than that with 
 which they are accustomed from earthly views 
 that, for a moment, these white sails appear to 
 be suspended in the sky. 
 
 They near the coast-line which bends in a 
 rounded curve forming a well-known cape. Across 
 the wide mouth of the bay lies another rounded 
 cape and in the distance the huge neck of this 
 peninsula is seen to be a network of water and 
 earth. They near the coast and note that the 
 earth below them has become a vast waste of sand, 
 low land, and tidal sloughs. They bank to the 
 right and follow the coast-line. Ahead of them 
 
THE SUPREMACY OF AIR-TRAVEL 181 
 
 is a long sliver of bright barren sand extending for 
 many miles and losing itself in tbe haze off the 
 coast of an adjacent state. The earth below be- 
 comes a complete waste, for the trapezoidal areas 
 of cultivated land showing by their straight-line 
 boundaries the hand of man, have now entirely dis- 
 appeared. A few vessels dot the thousands of 
 square miles of ocean surface visible to their 
 left, but the lonely expanse of water is populous 
 compared with the many square miles of waste 
 below them. 
 
 The coast-line of the state to the south of them 
 unfolds and they are able to detect the chief char- 
 acteristics of the arms of the ocean which give to 
 the eastern boundary its irregular outline. Be- 
 yond all this extent of coast-line they see the be- 
 ginning of the second state to the south. Below 
 them the topography is still the same swampy 
 waste but near the coast it is cut by many shallow 
 indentations as indicated by the yellowish tint of 
 the water. After continuing a few miles beyond 
 the boundary of this adjacent state they describe 
 a huge arc and head westward. Their course now 
 leads them across the heart of this extensive 
 swamp. Down below, the earth appears to be cov- 
 ered by a vast forest. Indentations of water have 
 disappeared to the rear but they detect the sparkle 
 of water here and there amid the dark green 
 foliage of the timber. They are now over one of 
 the great wooded swamps of the country. Ahead 
 of them lies a circular lake two or three miles in 
 
182 THE BOOK OP THE SKY 
 
 diameter, alone, without apparent inlet or outlet 
 amid this area of wooded waste. 
 
 They have often discussed the results of a 
 forced landing on top of this scrubby timber and 
 have decided that a congested district of a city 
 would be more suitable. Here, with many miles of 
 swampy woodland between them and civilization, 
 the only succor which could arrive in time to be 
 of value to them would be a dirigible balloon. 
 Their tattered craft in the treetops woUld point 
 the way and their rescue may be left to the imagi- 
 nation. Despite these thoughts they are tempted 
 to see this dark forbidding swamp at closer 
 range. 
 
 Far beyond them in the distance the familiar 
 areas of cultivated fields are seen making their 
 way into the outskirts of this waste. With these 
 distant fields in view their altitude insures com- 
 parative safety; however, they throttle the motor 
 and glide downward. The details below them rap- 
 idly grow larger and soon they see the water 
 glinting everywhere through the treetops. They 
 continue their downward glide and as the altitude 
 decreases, the swamp appears more forbidding. 
 Their nerves grow more tense and their eyes and 
 ears are alert. A single "miss" of their motor 
 would lead to immediate action. Down and down 
 they glide and, finally, risking the chance of a 
 failing they dip for a skim over the treetops. Just 
 before they reach their low point the throttle is 
 opened and with a roar of disdain the motor pulls 
 
THE SUPREMACY OF AIR-TRAVEL 183 
 
 them rapidly upward out of reach of the watery 
 waste. They have been within a hundred feet of 
 the heart of the swamp, an added thrill to their 
 journey. 
 
 They continue to climb and when the earmarks 
 of civilization appear below them they are at an 
 altitude of many thousand feet. Large cities lie 
 in the distance as shown by the characteristic 
 smoky haze. They alter their course toward them 
 and soon the details of the cities become visible. 
 Their altitude is again fifteen thousand feet ias 
 they soar over them. The details of the harbor, 
 the little thread-like wharves, the alignment of the 
 tiny city blocks, the parking along the waterfront, 
 and a vast number of details of two large cities are 
 spread in miniature nearly three miles below 
 them. Their craft is a tiny speck to the inhabi- 
 tants below and doubtless is not seen. The posi- 
 tion of their landing field can be distinguished 
 several miles inland beyond the far shore of the 
 wide strip of water below them. They know that 
 it lies between the second and third arms of the 
 bay beyond, for the real map of the region as 
 seen from the heights of cloudland is well im- 
 pressed upon their memory. 
 
 As a safety valve for their nerves which are in 
 tension despite their calmness, they dip the craft 
 upward and topple into a nose-dive. Down they 
 go at a tremendous speed. The thousands of feet 
 of altitude rush past as the city spreads rapidly 
 and comes up to meet them. Then with a swoop- 
 
184 THE BOOK OF THE SKY 
 
 ing curve, they straigliten out and cross the sev- 
 eral miles of water toward home. They look back- 
 ward at the swampy region in the distance. At 
 their present low altitude it is merged into the 
 greater depths of haze. The horizon of the ocean 
 is no longer distinguishable because it lies beyond 
 through the maximum depth of haze. They are 
 back in the smudgy atmosphere of the earthly 
 world. The field rapidly spreads before them; 
 they dip into a gentle glide and land. 
 
 They have completed a trip which they have 
 made several times before. Superficially to them 
 it is merely a two-hour trip but they know that 
 the topography of the course on earth is such as 
 to mean months, perhaps a year, of the hardest 
 toil to cover the course in any other way. They 
 need no convincing regarding the supremacy of 
 air-travel. 
 
CHAPTER XVIII 
 
 METEOEOLOGY 
 
 "Knowledge alone is the being of Nature 
 Giving a soul to her manifold features." 
 — Bayaed Taylok. 
 
 METEOEOLOGY is the science of "things of 
 the air" and its development is extremely 
 important to civilization. The aspect of this sci- 
 ence which touches mankind in general is that 
 dealing with the weather, — past, present, and 
 future. Weather forecasts and storm warnings 
 as issued by the Weather Bureau are correct 
 about eight times out of ten despite the facetious 
 banter hurled at the official forecaster. The pres- 
 ent impossibility of obtaining simultaneous data 
 over a large portion of the globe and at sufficient 
 altitudes adds to the difficulties of forecasting in 
 such a matter as weather which has so many influ- 
 ences acting upon each other. Nevertheless, the 
 public should encourage the development of th6 
 science and should interest itself in those details 
 at least which pertain to the weather. Those who 
 will read the official forecasts and watch the signs 
 
 185 
 
186 THE BOOK OF THE SKY 
 
 in the sky will seldom become victims of a weatlier 
 surprise. 
 
 Meteorology is the science of the great sea 
 above which has always meant so much to man- 
 kind and now that the air has been invaded and is 
 to become a highway of travel, a widening useful- 
 ness of this science appears. The meteorologist 
 will be looked upon for prognostications regard- 
 ing ' ' flying ' ' weather. He will be expected to map 
 the air-currents in order that the traveler may 
 avoid unfavorable winds or may take advantage 
 of favorable ones. If the aerial traveler hitches 
 the wings of the wind to those of his craft he may 
 often increase his distance traveled in a given time 
 or reduce his time for a given distance very 
 greatly. Even the aerial traveler himself should 
 be acquainted with the general facts of meteor- 
 ology if he would be best equipped for venturing 
 into the air. On the other hand, air-travel doubt- 
 less will contribute much knowledge to this sci- 
 ence. 
 
 The earliest myths indicate that civilization be- 
 fore the dawn of history was interested in the 
 "things of the air." From early literature it is 
 possible to gain an idea of the climate of the coun- 
 try whence they came. Doubtless, there were per- 
 sons in all ages who acquired skill at forecasting 
 the weather but the first systematic records of 
 which there is any knowledge do not date back 
 farther than the twelfth century. These records 
 and those of succeeding centuries were entirely 
 
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METEOROLOGY 187 
 
 those of individuals until the middle of the nine-' 
 teenth century. During the latter half of the last 
 century national organizations began to take up a 
 systematic study of meteorology and today every 
 civilized nation has its weather bureau or meteor- 
 ological office. 
 
 The invention of the telegraph made it possible 
 to obtain simultaneous reports from many sections 
 of a country so essential to systematic study and 
 prognostication. The laying of the ocean cables 
 extended the area from which simultaneous re- 
 ports could be obtained and wireless telegraphy 
 made it possible for ships to exchange observa- 
 tions with land stations. Thus the web of stations 
 has been built up and with the addition of air- 
 travel, the development of meteorology should 
 grow apace. Today it may be said that weather 
 and storms may be predicted a day or two in ad- 
 vance with sufficient accuracy to be of valuable 
 service in many ways and to justify the cost of 
 such work. The science is so important and in- 
 teresting that every person should be stimulated 
 to give it at least casual attention. Furthermore, 
 it is such a vast field and so fraught with mys- 
 teries and difficulties that it should be attractive 
 to the best scientific talent. 
 
 Modern meteorology includes a study of all the 
 phenomena of the atmosphere of gases, dust, and 
 clouds which surround the earth and extend to 
 that unknown and undefined region of so-called in- 
 terstellar space. The collective influence of these 
 
188 THE BOOK OF THE SKY 
 
 many phenomena results in what is called climate, 
 hence, their collective study is that of climatology. 
 It is not the intention to go deeply into the sub- 
 ject of meteorology but a general view may 
 awaken in the reader an interest in the vast aerial 
 world now literally opened to him by the advent 
 of aircraft. Many details have been interwoven 
 in other chapters but repetition will be avoided in 
 so far as possible. At best, the present survey 
 will be merely a hurried one aiming to point out 
 the general aspects of an intricate science. 
 
 Obviously the content of the atmosphere is of 
 prime importance. Oxygen and nitrogen com- 
 prise nearly the total amount of the atmosphere. 
 The relative proportions of the various gases re- 
 main practically constant up to an altitude of 
 seven miles, or in the region of convection cur- 
 rents. The relative proportions of oxygen and 
 nitrogen vary only a fraction of one per cent over 
 the earth's surface and these variations seem to 
 be related to regions of high and low barometric 
 pressure. Carbon dioxide varies slightly with the 
 exposure of the locality to wind, increasing some- 
 what in proportion to the amount of shelter. It is 
 generally present in slightly greater amounts over 
 land than sea. These variations are of scientific 
 interest but not of everyday importance. 
 
 "Water-vapor is present in very small propor- 
 tions but these small amounts are exceedingly 
 important to mankind. Dry dust-free air is quite 
 transparent to the radiant energy from the sun, 
 
METEOROLOGY 189 
 
 but the presence of water-vapor makes it quite 
 absorbing of the so-called "heat rays." In fact, 
 on the average, only about sixty per cent of the 
 radiant energy from the zenith sun which is inci- 
 dent upon the upper atmosphere reaches the earth 
 on a clear day. As the sun decreases in altitude 
 the depth of atmosphere greatly increases, hence, 
 the greatest percentage of the energy from the 
 sun reaches the earth at noon. Clouds act as the 
 earth's surface and absorb and reflect most "bf 
 the radiant energy from the sun, hence, it is cool 
 in the shade of a cloud. 
 
 Interstellar space may contain molecules of the 
 highly volatile gases of the atmosphere which 
 escape from the earth's gravitational force. The 
 refraction of light, twilight, shooting stars, and 
 the aurora indicate that something material exists 
 in appreciable quantity as high as one hundred 
 miles at least. Shooting stars suddenly become 
 luminous by friction when they strike the upper 
 atmosphere. The aurora is supposed to be simi- 
 lar to electrical discharges in vacuum tubes, and 
 is generally accounted for by the presence of 
 electrons expelled from the sun and sent out 
 through space, finally to produce luminous dis- 
 plays in the extremely rarefied regions at the out- 
 skirts of the atmosphere. 
 
 The circulation of the atmosphere is perhaps, 
 the most important phase of meteorological 
 studies, for weather and climate are dependent 
 jipon it. Doubtless, in the heights of the atmos- 
 
190 THE BOOK OF THE SKY 
 
 phere quite free from the multitude of influences 
 found at or near the earth's surface, weather and 
 climate are synonymous — always the same. How- 
 ever, in so far as mankind is immediately con- 
 cerned the large local changes in weather are due 
 to the mechanical and thermodynamic interaction 
 of earth, ocean, and atmosphere. The Avinds are 
 fascinating in their magnitude, variety, and rela- 
 tions to each other and to other phases of meteor- 
 ology. Systematic studies and simultaneous re- 
 ports have done much toward ascertaining the 
 laws of these supposedly whimsical and unruly 
 currents. Owing to their importance they are 
 treated in another chapter. They have been 
 studied at high altitudes by observations on clouds 
 and by means of kites and balloons. The clouds 
 reveal much pertaining to the winds and they are 
 available to the amateur as well as to the meteor- 
 ologist. 
 
 In the development of theories, so essential for 
 the purpose of scientific explorations, the meteor- 
 ologist must obtain all the physical data possible 
 pertaining to the air. Therefore, he studies such 
 physical characteristics as specific heat, density, 
 expansion, elasticity, diffusion, viscosity, friction, 
 gravity, temperature, and pressure. 
 
 Cloudiness is a factor in climate and the details 
 of the clouds reveal much to the forecaster ; conse- 
 quently, reports of types of clouds are recorded 
 and the percentage of cloudiness is determined 
 daily at various stations. The average cloudiness 
 
METEOROLOGY 191 
 
 is intimately related to tlie density and circulation 
 of the atmosphere. 
 
 The apparatus used by the meteorologist in re- 
 cording the manifold observations are very exten- 
 sive. Many of these are recording instruments 
 which eliminate the necessity for personal atten- 
 tion. Such recording instruments are obviously 
 of great value for attaching to kites and to 
 balloons. By means of them attached to small 
 balloons, data pertaining to the atmosphere as 
 high as twenty-two miles have been obtained. 
 
 Various types of thermometers are used vary- 
 ing in principle, range, and sensitiveness. 
 
 Barometers record the atmospheric pressure. 
 These are of various types. The altimeter used 
 on aircraft is merely a barometer of the aneroid 
 type which is calibrated to read altitudes instead 
 of atmospheric pressures, there being a known 
 relation between these two factors. 
 
 The anemometer measures the velocity of the 
 wind. Those used at land stations consist usually 
 of cups which revolve in the wind at the end of 
 arms. The speed indicator of aircraft is really a 
 wind-gauge of another type and measures the 
 speed of the craft in relation to the air. Obviously, 
 this does not measure the speed of the craft in 
 relation to the earth. An airplane capable of a 
 speed of one hundred miles an hour in still air, 
 on heading into a fifty-mile wind, has a speed in 
 reference to the earth of only fifty miles an hour. 
 However, in the opposite direction its speed in 
 
192 THE BOOK OF THE SKY 
 
 reference to the earth would be one hundred and 
 fifty miles an hour. This accounts for some of 
 the "record" flights commonly reported. 
 
 The hygrometer indicates or records the rela- 
 tive or absolute humidity of the air, and, there- 
 fore, yields data pertaining to the quantity of 
 water-vapor present. The quantity of water- 
 vapor which air will hold before it becomes "full" 
 or saturated increases with the pressure and tem- 
 perature, hence, these quantities must be consid- 
 ered in connection with hygrometer records. 
 
 Eain and snow gauges supply the data pertain- 
 ing to precipitation. These are usually simple 
 receptacles but their forms have been the subject 
 of careful study. 
 
 By means of the evaporometer the quantity of 
 water evaporated from a given area is determined. 
 Obviously, this is determined by the "thirstiness" 
 of the air, that is, by its relative humidity. The 
 rate of evaporation, other things being equal, is 
 directly proportional to the difference in tempera- 
 ture indicated by wet and dry bulb thermometers. 
 It increases with the wind velocity. Sea-water 
 evaporates five per cent less rapidly than fresh 
 water. The size and shape of the area from which 
 evaporation takes place influence the rate of 
 evaporation. 
 
 Various devices are available for determining 
 the direction and apparent velocity of a cloud. 
 The heights of clouds may be determined by tri- 
 angulation, that is, by taking simultaneous obser- 
 
METEOROLOGY 193 
 
 vations at two points at a sufficient distance apart. 
 
 Several types of sunshine recorders are in use. 
 They are based on chemical and thermal princi- 
 ples. Obviously, sunshine may be recorded pho- 
 tographically or by charring a moving paper in 
 the focus of a lens. 
 
 Various kinds of electrical apparatus are in use 
 to obtain electrical data pertaining to the atmos- 
 phere too varied and too specialized for discus- 
 sion here. 
 
 Dust particles are important from various 
 standpoints. They absorb sunlight and they de- 
 crease visibility but they are useful as nuclei 
 upon which water-vapor condenses. If an en- 
 closed glass vessel contains a layer of water, the 
 air above the water will be saturated. If the 
 capacity of this air for water-vapor be reduced in 
 any manner, such as by suddenly reducing the 
 pressure, a cloud will be seen to form. This ex- 
 periment may be performed easily by having a 
 rubber tubing connected to the bottom of the ves- 
 sel and to another vessel containing water. The 
 reduction in the pressure of air in the former may 
 be obtained by suddenly lowering the latter. By 
 raising the latter to its original level the original 
 conditions may be obtained again. After repeat- 
 ing the process two or three times, each time per- 
 mitting the cloud to settle upon the water, it will 
 be noted that the cloud will no longer form. The 
 dust nuclei have been used up. If cigar snaoke or 
 electrified air be admitted, a dense cloud wiU be 
 
194 THE BOOK OF THE SKY 
 
 easily formed. Dust counters are used by the 
 meteorologist and it has been found that the num- 
 ber of dust particles in a given volume or mass 
 of air decreases greatly with altitude and varies 
 with locality 
 
 The brightness of the sky is of importance and 
 is measured by means of a photometer. The blue- 
 ness of the sky is also recorded. 
 
 The intensities of visible sunlight and of total 
 radiant energy from the sun are studied sys- 
 tematically. 
 
 The preceding paragraphs indicate in the brief- 
 est manner, the intricate web of the science of 
 "things of the air." From systematic records 
 much has been learned of the laws of the wonder- 
 world above the earth's surface, but much remains 
 to be explained. However, weather-prognostics 
 are now upon a basis of fact and are fairly reli- 
 able. Although weather forecasting is not the 
 sole aim of the meteorologist, it is the most im- 
 portant phase as far as mankind in general is 
 concerned. 
 
 The barometer is perhaps the best single tool of 
 the forecaster. Immediately after its invention, 
 nearly two hundred years ago, systematic observa- 
 tions showed that, in general, a low barometric 
 pressure preceded rain or snow; and a high 
 pressure attended fine weather. The systematic 
 simultaneous observation of atmospheric press- 
 ure, of temperature, of direction, and of velocity 
 of the wind and of the condition of the sky at many 
 
METEOROLOGY 195 
 
 places yields mucli data which, when placed upon 
 weather charts, make it easy for the meteorologist 
 to prognosticate with a fair degree of accuracy. 
 The paths of cyclones or areas of low pressure are 
 fairly well established by previous records. 
 
 Everyone knows, in a general way at least, that 
 the Weather Bureau issues such maps daily. If 
 one will take the pains to interest himself more in 
 these weather maps he wiU find much interest in 
 watching the progress of the cyclones and anti- 
 cyclones across the country. The former are en- 
 closed by more or less circular lines (isobars) each 
 of which represents the regions possessing the 
 same barometric pressure. The anticyclone is the 
 region of high pressure and is enclosed by isobars 
 each indicating the localities of the same baro- 
 metric pressure. 
 
 Systematic data on temperature show that many 
 meteorological elements, which otherwise may 
 appear capricious, to be related to the isotherms 
 (the lines connecting localities of equal tempera- 
 tures). Such data have revealed a definite part 
 played by the distribution of land and sea, for 
 example : 
 
 In the days of sailing vessels the systematic 
 tabulation of winds at sea resulted eventually iu 
 shortening many ocean voyages because the skip- 
 per was enabled to take the course showing gen- 
 erally favorable winds, and he learned also to 
 avoid the doldrums or extensive equatorial calms. 
 
 Average statistics numerically represent cli- 
 
196 THE BOOK OF THE SK5f 
 
 mate but are of little value in foretelling the 
 weather. The daily records combine to show the 
 weather over a large section of the earth and then 
 serve as statistics from the accumulation of which 
 many generalizations have been discovered. 
 
 The science of meteorology still rests largely 
 upon pure observation. The "synoptic" charts 
 compiled from observations taken at the same 
 time of day enable the meteorologist to take a 
 bird's eye view, as it were, of the weather condi- 
 tions over the country from day to day. From 
 these charts it has been discovered that the con- 
 figuration of the isobars assumes several weU-de- 
 fined forms; that the wind takes certain definite 
 directions relative to the trend of these lines ; that 
 the velocity of the wind is usually proportional to 
 the closeness of the isobars; that the weather is 
 related to the shape of these lines ; that the posi- 
 tions of these lines are constantly shifting; that 
 many other details of weather are usually related 
 to the isobars in a systematic manner. 
 
 The whole meteorological scheme which appears 
 chaotic to the casual observer becomes very much 
 simplified when analyzed, and gradually by the 
 accumulation of records, the tangled web is being 
 unraveled. 
 
CHAPTER XIX 
 
 WINDS 
 
 "Wild spirit which art moving everywhere, 
 Destroyer and preserver; hear, oh, hear! 
 Thou on whose stream, 'mid the steep sky's commotion 
 Loose clouds like earth's deca/ying leaves are shed, 
 Shook from the tangled boughs of heaven and ocean, 
 Angels of rain and lightning; there are spread 
 On the Hue surface of thine airy surge. 
 Like the bright hair uplifted from the head 
 Of some fierce Maened, even from the dim verge 
 Of the horizon to the zenith's height. 
 The locks of the approaching storm." 
 
 — Shelley. 
 
 THE casual observer perhaps thinks of the in- 
 visible ocean of air as mere space but on 
 further thought he must attribute weight or mass 
 to this invisible sea. The barometer indicates that 
 mankind lives at the bottom of a fluid which exerts 
 a mean pressure at sea-leyel of slightly less than 
 fifteen pounds per square inch. This pressure is 
 ordinarily unnoticed by man because it is equal- 
 ized throughout the porous structure of his body. 
 However, when he ascends to high altitudes in an 
 
 197 
 
198 THE BOOK OF THE SKY 
 
 aircraft or up the mountain side, he notes symp- 
 toms which he has learned to attribute to de- 
 creased atmospheric pressure. Man lives at the 
 bottom of this sea which rapidly diminishes in 
 pressure and density as he ascends from the bot- 
 tom. From various considerations the extreme 
 upper limit of this atmospheric ocean is at an alti- 
 tude of from fifty to one hundred miles, but the 
 pressure decreases so rapidly with altitude that 
 the upper surface is not defined as is that of the 
 less compressible and less volatUe sea of water. 
 In fact, the airman has left half the total weight 
 of air below him before he reaches an altitude of 
 four miles and this rapidly diminishing density 
 limits the heights to which baUoons and airplanes 
 may ascend. 
 
 Air, having the property of mass in common 
 with all material substances, also possesses inertia 
 and it is this property that lends force to the wind 
 which drives windmills, speeds schooners on their 
 way, and blows down trees. The propeller of an 
 aircraft encountering this inertia of the air, which 
 it possesses by virtue of its mass, propels the 
 craft through this invisible sea inuch in the same 
 manner that the submarine is pi^opelled in the 
 ocean of water. 
 
 The magnitude of this ocean of air and a con- 
 ception of the force of its currents perhaps may 
 be obtained from some approximate figures. The 
 average pressure of air on each square foot of the 
 earth's surface is approximately one ton. The 
 
WINDS 199 
 
 weight of the air above each square mile of the 
 earth's surface is approximately thirty million 
 tons. The area of the surface of the earth being 
 approximately two hundred million square miles, 
 the total weight of the ocean of air is represented 
 by an incomprehensible value, namely, about six 
 billion million tons. 
 
 The general circulation of this mass of air de- 
 termines weather and climate and is now of a 
 new importance inasmuch as mankind has learned 
 to ascend from the bottom of this sea and navigate 
 its lower strata. There are certain great general 
 movements of the air, upon which many minor 
 currents are superposed. A river affords an 
 analogy with its bends, eddies, whirlpools, ripples, 
 backwaters, and varying currents, but despite 
 these, there is the general trend. 
 
 Atmospheric circulation is a gravitational phe- 
 nomenon caused by temperature differences ; that 
 is, it is due to the different weights of equal vol- 
 umes of air of different temperatures. The circu- 
 lation of water of different temperatures is a help- 
 ful analogy. "Water in heating or cooling systems, 
 in the teakettle or in the ocean, circulates in a 
 complex, though law-abiding manner. The mag- 
 nitude of the atmosphere, the manifold influences, 
 the lack of data pertaining especially to high alti- 
 tudes and latitudes, render it impossible at pres- 
 ent for meteorologists to explain atmospheric eir- 
 feulation completely or to map out all the details. 
 
 The heated air in the equatorial region rises 
 
200 THE BOOK OF THE SKY 
 
 and there is a higher pressure established at the 
 equator than at the poles. As a consequence of 
 this pressure gradient, air flows toward the poles. 
 On its way toward the polar regions it cools and 
 sinks toward the earth, eventually to return to the 
 equatorial region to begin its cycle again. Some 
 of this air returns near the surface of the earth 
 but it is thought that high up in the stratosphere, 
 in regions above ten miles, there may be steady 
 winds from polar regions toward the equator. This 
 conclusion seems plausible because the tempera- 
 ture of that high region is lower over the equator 
 than over regions of higher latitude. 
 
 Such permanent temperature contrasts are 
 chief factors in atmospheric circulation. On a 
 very much smaller scale are the land and sea 
 breezes. During a summer's day the land heats 
 more rapidly than the sea; hence, the air rises 
 over the land and a pressure difference or gradi- 
 ent is established. The air from over the sea 
 flows over the land in a natural attempt to equalize 
 this pressure; hence, the sea breeze is born. At 
 night the land cools more rapidly than the sea and 
 it finally becomes colder than the water. A land 
 breeze then flows out over the water. These cur- 
 rents are gentle as a rule and do not extend far 
 inland or to sea. 
 
 If the earth's surface were smooth and of a uni- 
 form composition and if the earth did not rotate 
 about its axis, the general circulation of the atmos- 
 phere doubtless would be simple. Air would rise 
 
WINDS 201 
 
 from, the equator and flow north and south to the 
 respective poles and return in simple paths. How- 
 ever, there are many factors which influence the 
 general circulation of the atmosphere, a very im- 
 portant one being the rotation of the earth. Any 
 mass at the equator possesses a certain momentum 
 proportional to the velocity of the surface of the 
 earth due to a,xial rotation. The west-to-east 
 velocity of a point on the equator is about one 
 thousand miles an hour, hence, the rising equa- 
 torial air possesses this velocity toward the east. 
 The pressure gradient from equator to pole causes 
 the air to tend to flow' north in the northern 
 hemisphere, but owing to the west-to-east velocity 
 of the air, its actual path is toward the northeast. 
 This point will be clearer if it be noted that the 
 velocity of the earth's surface due to axial rota- 
 tion diminishes gradually to zero at the poles. As 
 the equatorial air reaches higher latitudes its 
 "equatorial" west-to-east velocity causes it to 
 "get ahead of the earth"; hence, in this hemi- 
 sphere it sheers toward the right as it travels 
 toward the north pole. 
 
 This tendency toward the right adds one of the 
 many influences which result in extreme com- 
 plexity by building up a pressure gradient from 
 east to west, because the air tends to pile up on 
 the right and diminish on the left. Of course, there 
 is a very great resultant retardation due to fric- 
 tion, viscosity, and many other causes. This cur- 
 rent gradually descends as it leaves the equator; 
 
202 THE BOOK OF THE SKY 
 
 behind and in the temperate zones is practically a 
 surface wind. This may give a glimpse of some 
 of the chief influences which are the laws behind 
 the general circulation of the atmosphere. Per- 
 haps a further idea of the causes of aerial cur- 
 rents may be gained from brief discussions of 
 characteristic winds. It is understood that the di- 
 rections of winds are those from which they blow. 
 For example, a west wind is one blowing from 
 west to east or a current in which the air is travel- 
 ing from west to east. 
 
 The foregoing accounts for the prevailing 
 westerly winds in the United States but, of course, 
 there are permanent and temporary diverting in- 
 fluences. The distribution of land and sea ac- 
 counts for certain temperature differences of suf- 
 ficient magnitude and extent to become a powerful 
 influence upon the course of even the great flow 
 of air from equator to pole and return. These 
 temperature differences depend upon the season 
 and may actually reverse from summer to winter. 
 Hence, there arises certain prevailing winds with 
 respect to land, water, and season. 
 
 On a more local scale the topography of the 
 earth may cause a permanent diversion of the gen- 
 eral trend of the wind. But all these prevailing 
 winds in the stratum of air below an altitude of 
 seven miles in this zone are continually being influ- 
 enced and even temporarily overcome by cyclonic 
 storms, anticyclones, and even the more local dis- 
 turbances. 
 
WINDS 203 
 
 If air is heated locally, whirlwinds may be gen- 
 erated; cumulus clouds may be formed by con- 
 densation of the water-vapor due to the cooling of 
 the rising vapor-laden air ; breezes may flow down 
 valleys to replenish rising air; sea breezes may 
 blow inland to replace the air which rises over 
 the heated land. 
 
 If air is locally cooled, breezes may blow from 
 land to sea at night or in winter; air may fall 
 down from mountain tops, giving rise to mountain 
 breezes; winds may blow out of the cavities of 
 glaciers or out of caves ; various local winds may 
 arise from cooled sources; the sluggish drainage 
 winds over extensive areas known as continental 
 fall-winds are formed. The ice-caps of Greenland 
 and of Antarctica produce strong and fairly con- 
 tinuous fall-winds. These extensive cold areas 
 control the direction and velocity of the local 
 winds of the regions and are so extensive as to 
 influence the general circulation of the atmosphere 
 over large portions of the globe. The extensive 
 area of Antarctica and its low temperature cause 
 strong continuous surface winds averaging in 
 some localities on the edge of this polar cap as 
 high as fifty miles per hour for the entire year. 
 
 If extensive areas are continuously heated and 
 cooled respectively, gradient winds are born such 
 as those across flat desert regions. Besides these 
 are the trades, antitrades, monsoons, cyclonic 
 winds, and anticyclonic winds. Over level regions 
 gentle gradient winds are of highest velocity in the 
 
204 THE BOOK OF THE SKY 
 
 early afternoon and are least at about dawn. 
 Their depth above the earth's surface is usually 
 only a few hundred feet which is less in winter 
 than in summer. There is a tendency of the wind 
 to change slightly during the day with the sun, that 
 is, to follow the hottest region. Obviously, this 
 weak tendency is usually masked by more power- 
 ful influences. 
 
 The normal state of atmospheric circulation in 
 middle latitudes is a definite west-to-east velocity, 
 therefore, other winds and calms are really dis- 
 turbances. 
 
 The trade winds are very constant over the 
 tropics and are peculiar to the oceans. They usu- 
 ally have a large east-to-west component. In the 
 higher latitudes of the tropics of the northern 
 hemisphere they generally blow from the north- 
 east, that is, they are northeasterly winds. As 
 they approach the equator they tend to become 
 east winds. Their steadiness, upon which early 
 commerce depended, won for them their name. 
 
 Calms, of course, may appear any place if there 
 is no pressure gradient, but the doldrums near the 
 equator are famous. They are found in peculiar 
 depressions between the northeast trades of the 
 northern hemisphere and the southeast trades of 
 the southern hemisphere. The southeast trades 
 gradually change to east winds as they progress 
 north toward the equator in qidte the same man- 
 ner as trades of the northern hemisphere. 
 
 The heated air which rises from the equator to 
 
WINDS 205 
 
 begin its journey toward the poles changes, in the 
 northern hemisphere, from an east wind near the 
 equator to southeast, south, southwest as it pro- 
 gresses northward, becoming nearly a west wind 
 as it enters the temperate zone. That portion 
 which goes south changes in a similar manner 
 from an east wind to northeast, north, northwest 
 and finally becomes practically a west wind as it 
 enters the south temperate zone. 
 
 The antitrades are of the same depth as the 
 trades and are merely an overhead continuation 
 of the latter. The trade winds ascend as they ap- 
 proach the equator and flow poleward, thus pro- 
 ducing the antitrades of general atmospheric cir- 
 culation. They return eventually to the equator 
 to begin again their cycle, from trades to anti- 
 trades, and finally to westerlies of middle lati- 
 tudes. These, of course, are modified by many 
 secondary air-currents, storms, etc. 
 
 Monsoons are the winds caused by seasonal dif- 
 ferences in the temperatures of land and water 
 and, therefore, bear the same relation to summer 
 and winter as the land and sea breezes bear to 
 night and day. 
 
 Thunderstorm winds are due to excessive tem- 
 perature contrasts of adjacent local heating and 
 cooling. Shortly before a thunderstorm takes 
 place at a given locality, a south wind may be 
 blowing. When the storm is near, the wind begins 
 to blow from the storm and when rain is close 
 the wind becomes violent from the storm front. 
 
THE BOOK OF THE SKY 
 
 This wind is usually gusty for a few minutes, then 
 becomes steady. After the storm has passed the 
 wind generally assumes its original direction. 
 
 There are many definite forced winds caused by 
 other winds or by the earth's contour. These may 
 be represented by tornadoes, water-spouts (torna- 
 does over water), chinooks, and various eddies. 
 The earth's contour and various obstructions obvi- 
 ously cause eddies. The chinook or foehn is a 
 dry wind blowing down a mountain slope. The 
 tornado usually precedes a thunderstorm and ap- 
 parently the whirl is induced by adjacent strong 
 currents of air flowing in opposite directions. 
 When the circular path is once established, a 
 well-known physical law accounts for the tremen- 
 dous velocity in the small part of the funnel near 
 the earth. There is a tendency for the product 
 of the velocity times the radius of the circular path 
 to remain constant ; therefore, as the cross-section 
 diminishes toward the lower small end of the fun- 
 nel, it is obvious that the velocity must greatly in- 
 crease. Velocities as high as five hundred miles 
 per hour are estimated to exist in the smaller por- 
 tions of the funnel of a tornado, but the actual 
 translational velocity is low, usually about twenty- 
 five miles per hour. Tornadoes are peculiar to the 
 United States and invariably travel from west to 
 east, usually toward the northeast. They are 
 often called cyclones but in meteorological term- 
 inology the term cyclone is applied to a storm of 
 much greater area and is a system of winds whose 
 
WINDS 207 
 
 center is an area of low barometric pressure or a 
 "low" as it is called. 
 
 Tlie cyclone and its antithesis, the anticyclone, 
 are perhaps the most important atmospheric phe- 
 nomena to mankind, for they usually dominate the 
 local weather conditions. Strong winds and heavy 
 rain or snow in the temperate zone are associated 
 with a barometric "low." Moderate and gentle 
 winds and a clear sky are associated with a baro- 
 metric "high." The anticyclone is the system of 
 winds whose center is the "high." The average 
 diameter of a cyclonic storm in the United States 
 is at least one thousand mUes. Although some of 
 these cyclones remain stationary or nearly so and 
 thus may be termed semi-permanent, they travel 
 in general at an average speed of about twenty 
 miles per hour, in a general west-to-east direction 
 in middle latitudes. In the northern hemisphere 
 they generally have a southerly dip over conti- 
 nents and a northerly dip over oceans. These 
 storms from the west coast of the United States 
 travel generally eastward, with a southerly dip in 
 the region of the Great Lakes, then following the 
 direction of the St. Lawrence river, they leave this 
 continent through Newfoundland. 
 
 The direction of the winds in a cyclonic storm- 
 center may be described briefly in the following 
 cycle: counter clockwise around the barometric 
 low, spirally inward and upward, thence, outward 
 as they gain altitude. This process takes moist 
 air to high altitudes where the filmy clouds which 
 
208 THE BOOK OF THE SKY 
 
 are formed are spread by the high winds of the 
 upper regions over a large front far in advance 
 and to the sides of the storm-center. The cyclone 
 is a huge whirlwind usually of hundreds of miles 
 in diameter. The anticyclone is the system of 
 winds blowing out of a central "high." These 
 *' highs" and "lows" are seen on the weather 
 maps and one may find a fascination in viewing 
 the progress of these large disturbances across 
 the continent. Such maps are bird's-eye views of 
 the essential meteorological data in connection 
 with the general weather of the entire country. 
 From systematic observation of these maps and 
 of the sky one will be rewarded by much of inter- 
 est and eventually by a comprehensive knowl- 
 edge of the laws and eccentricities of weather. 
 
 In the preceding paragraphs an attempt has 
 been made to give not only a general idea of at- 
 mospheric circulation but also to present the 
 characteristics of various distinct types of winds 
 and their causes. It is seen that there are many 
 factors which influence the currents in the aerial 
 world. Even the earth's rotation is a funda- 
 mental influence, and besides the resultant effect 
 already mentioned, there is the effect of the curv- 
 ature of the earth. The deflective force due to the 
 earth's rotation and the horizontal component of 
 the centrifugal force due to the curvature of the 
 path are at right angles to the course of the ex- 
 tensive winds from the equator to the poles, hence, 
 
WINDS 209 
 
 they affect the direction of these winds. The 
 pressure gradient due to gravity not only influ- 
 ences the direction but also the speed of winds. 
 
 It is well known that winds increase in velocity 
 with elevation. The actual velocity close to the 
 surface of the earth is very irregular and it in- 
 creases with elevation more rapidly when the 
 average velocity is high than when low. There 
 is usually a rapid increase in velocity up to an 
 elevation of about one thousand feet above the 
 surface of the earth. Obviously, this is the region 
 where surface friction and the disturbances and 
 retardation therefrom are effective. Next there is 
 a region, from about one thousand to five thousand 
 feet, of irregular winds very slowly increasing 
 in velocity with altitude. Throughout the region 
 from elevations of about one to seven miles, the 
 velocity of the winds increases steadily with alti- 
 tude in the middle latitudes. These winds, out of 
 reach of frictional retardation and the ordinary 
 vertical convection currents, possess velocities 
 quite proportional to the pressure gradients. 
 These velocities reach two hundred miles per 
 hour. In the stratosphere, that is, above seven 
 miles in the temperate zone, the average velocity 
 appears to be less than just below it. 
 
 Although there are many uncertainties pertain- 
 ing to atmospheric circulation, some generalities 
 have been arrived at which may be of interest. 
 Apparently there is no great overflow of air at 
 
210 THE BOOK OF THE SKY 
 
 all in localities from the equator to the polar ice- 
 caps. At elevations of six or seven miles the wind 
 seems to have southerly components as frequently 
 as northerly components. This is an indication 
 that the circulation from the equator toward the 
 poles is complex at even higher altitudes. The 
 equatorial winds are not consistently easterly at 
 all altitudes. In fact, west winds are observed at 
 altitudes of ten to twelve miles and east winds 
 have been observed at higher altitudes. There 
 are strata of air in which the temperature some- 
 times increases with elevation and sometimes re- 
 mains stationary. This condition has been ob- 
 served in various localities from the equator to 
 the polar regions. The pressure gradient of the 
 upper atmosphere toward the poles is small in 
 the polar regions and reaches a low value even 
 in the northern portion of the temperate zone. 
 Furthermore, the winds in the polar regions are 
 not consistently westerly. The upper winds are 
 exceedingly variable in certain regions. 
 
 The phenomena of the circulation of the atmos- 
 phere are numerous and their combined influences 
 make a complex web. However, the subject may 
 be easily studied by anyone and surely the advent 
 of the aerial age has made the winds a subject 
 of general interest. Winds do not merely whip 
 the clouds into interesting and beautiful forms, 
 thereby revealing themselves and adding variety 
 to the sky, but they serve very useful purposes. 
 
WINDS 211 
 
 They help to make this earth inhabitable. Now 
 that man has invaded the aerial world he must 
 learn more of the winds so that he may avoid 
 those which do not suit his purpose and harness 
 those which do. 
 
CHAPTEE XX 
 
 WEATHER AND THE SKY 
 
 "And the hooded clouds, like friars, 
 Tell their heads in drops of rain." 
 
 — Longfellow. 
 
 TT is astonisHng that tte sky with its variety 
 -■- of beauty and moods does not have more ad- 
 mirers and interested observers. It can not be 
 that it is outclassed by other areas or aspects of 
 Nature because it occupies a prominent position 
 in landscapes and it is usually a dominating area. 
 Furthermore, its displays often overwhelm other 
 aspects of Nature in variety of color, pattern, and 
 mood. It is the only part of the great open places 
 that foUows civilization into its bewailed cities. 
 But it is even more astonishing that the sky does 
 not attract more observers with its utility as a 
 weather-indicator so definitely established. The 
 average city-dweller and many villagers look with 
 awe upon the ability of the farmer, the sailor, the 
 woodsman, and others who live in the open places 
 to foretell the weather. And this ability assumes 
 an uncanniness because the forecasts of these 
 
 212 
 
WEATHER AND THE SKY 213 
 
 prophets are so often made either in. picturesque 
 weather-lore or in such a manner as to bestow 
 the ability of self-expression to inanimate objects 
 apparently unrelated to the weather. For ex- 
 ample, the Indians had a sure sign of pending 
 rain when the "scalps" hanging among their 
 trophies became damp. Obviously, if these ob- 
 jects are hygroscopic they will get limp or damp 
 in humid air just as salt and cellar-walls indicate 
 humidity, and such moist air is often the fore- 
 runner of rain. 
 
 Doubtless, most of the weather-lore was fairly 
 dependable in the localities in which it originated 
 and, notwithstanding the fact that it usually ex- 
 presses weather-signs indirectly, it may often be 
 traced to a logical source. It appears that most 
 of it evolved from the accumulated experiences 
 of years of everyday observation of the sky and 
 the weather. However, the weather-signs differ 
 somewhat in various parts of the world; hence, 
 those sayings which have been transplanted into 
 regions remote from their sources are liable to 
 appear to be merely "rhyme" without the "rea- 
 son." Nevertheless, it is interesting and worth 
 while to analyze the weather-lore which has been 
 handed down through many generations and to 
 attempt to ascertain its foundations. In other 
 words, it is hardly safe to laugh at the picturesque 
 sayings of the weather-wise layman regardless 
 of their apparent lack of connection with the sky 
 or with other direct weather-signs. 
 
214 THE BOOK OF THE SKY 
 
 However, meteorologists during the past fifty 
 years have gathered so much scientific data per- 
 taining to the winds, the sky, and barometric pres- 
 sure, that it is easy, to base weather-prognostics 
 upon these facts. This adds another interesting 
 phase to the appreciation of cloudland. 
 
 The cyclonic storm and the anticyclone are such 
 important factors in the weather that a brief con- 
 sideration of them will reveal the portent of 
 many of the weather-signs in the sky. As already 
 indicated, the cyclone is a huge system of winds 
 surrounding a region of low barometric pressure. 
 The weather-maps may show the distribution of 
 pressure, the direction and velocity of the wind, 
 the character of the sky, and the kind of weather 
 in various regions of the cyclone. As one of these 
 storms approaches and passes over a given lo- 
 cality, the sequence of the essential details is more 
 or less as follows: clear sky, cirrus clouds, east 
 wind, denser cirro-stratus, stratus, cumulo- 
 nimbus, a rainy period, mists, west wind, squalls, 
 final shower, breaking clouds, clear sky. 
 
 In the United States the shape of these cyclones 
 is such that the region of low barometer or the 
 storm-center is not in the center of the cyclone. 
 This "low" is usually not as far from the north- 
 ern and western edges as from the other edges. 
 Inasmuch as these cyclonic storms travel gener- 
 ally from west to east, the sky-signs are farther 
 in advance of the storm-center than to the rear. 
 
WEATHER AND THE SKY 215 
 
 Likewise, they extend much farther south than to 
 the north. 
 
 If the reader will vislialize this cyclonic storm 
 as described in the chapter on "Winds" the 
 changes in the direction of the wind become obvi- 
 ous. In general, the winds are blowing toward 
 the center, although their actual paths may be 
 loosely described as spirals. Before the actual 
 storm-center arrives, the wind is easterly, that is, 
 toward the west and the storm-center. They shift 
 gradually as the storm-center approaches and 
 finally after it passes, the winds are westerly, 
 though still toward the storm-center. The actual 
 directions during this shift depend somewhat upon 
 whether the storm-center passes directly over or 
 to one side or the other of the observer's locality. 
 
 As has been mentioned several times in other 
 chapters, the cirrus clouds are formed by the 
 moist air drawn into the storm-center and pro- 
 jected to high altitudes where the moisture con- 
 denses. The high westerly winds of those upper 
 regions, from four to seven miles above the sea- 
 level, carry these fihny cirri far in advance of 
 the storm-center and they become weather-signs 
 for the cloud-wise. They foretell the approach of 
 the storm and only fail when the storm wears out 
 or shifts its course radically from the general 
 course of such storms. 
 
 But there are various forms of cirrus clouds, 
 some of which are fair-weather and others are 
 foul-weather clouds. There are many forms of 
 
216 THE BOOK OF THE SKY 
 
 pure hairy cirri which indicate fine weather while 
 others such as "mare's tails," "cat's tails," and 
 "goat's hair" are forerunners of foul weather. 
 In general, rapidly moving upper clouds signify 
 worse weather than those which move more slowly. 
 In some places the "mare's tails" usually indi- 
 cate approaching wind and "goat's hair" merely 
 rain. "Mare's tails" and "cat's tails" precede 
 the violent cyclonic storms known as hurricanes in 
 the tropics. "Mare's tails" are long straight 
 fibers of gray cirri; "cat's tails" are denser; 
 "goat's hair" is a short bunch of white fihny 
 cirrus fibers. All these are found in the outer 
 areas of a cyclone and after a little experience 
 they will be recognized as being intermediate be- 
 tween the cirrus stripes and the pure filmy veil- 
 like cirri attending fine weather. 
 
 Clouds and other weather-signs should be 
 judged with preceding conditions in mind. False 
 cirri may be formed in connection with cumulus 
 clouds and these may be mistaken for the cy- 
 clonic cirri. Toward evening thin cirrus-like 
 clouds sometimes appear similar in form to 
 "mare's tails" but these are often decadent 
 cumuli which soon disappear. Foul-weather cirri, 
 which herald the approach of a cyclonic storm, do 
 not disappear after sunset. If these gradually 
 thicken and the barometer steadily falls a storm 
 is not far away. Cirrus clouds precede the storm- 
 center by an interval of from ten to thirty hours. 
 The foregoing illustrates a general principle, 
 
WEATHER AND THE SKY 217 
 
 namely, tliat the same cloud-forms may not al- 
 ways indicate the same kind of weather. A gen- 
 eral knowledge of preceding weather and sky 
 conditions and of the formation of clouds is 
 necessary if the weather is to be foretold with a 
 fair degree of accuracy. 
 
 Wisps of thin cirri are formed in fine weather 
 by condensation in ascending air. Owing to the 
 low humidity during fine weather and the less 
 forceful ascension of air, these fair-weather cirri 
 are very thin and wispy. The foul-weather cirri 
 which are born in the cradle of the storm are gen- 
 erally denser and are likely to consist of longer 
 streamers crossing the entire sky. 
 
 The thin layer of cirro-stratus soon follows the 
 first appearance of foul-weather cirrus. This may 
 be considered merely a thickened layer of cirri 
 nearer the storm-center. It is this thin fog of ice 
 crystals at altitudes of five or six miles which is 
 responsible for a "watery" sun or moon and for 
 halos. The latter generally appear before the 
 former in the cyclonic cycle of events. The por- 
 tent of the halo has been incorporated in weather- 
 lore in many ways, an example of which is, — 
 
 "Last night the moon had a silvery ring 
 Tonight no moon we see." 
 
 Continuing toward the storm-center, fine rain 
 is next encountered which soon becomes driving 
 rain. In the storm-center squalls and heavy 
 
218 THE BOOK OF THE SKY 
 
 showers are common and, of course, there always 
 comes the clearing shower. 
 
 "When rise begins after low, 
 Squalls expect and clear blow." 
 
 As the center passes, the sky is full of broken 
 clouds and the rear of the storm is characterized 
 by cool dry air and a blue sky with well-defined 
 cumulus clouds. The conditions of the rear are 
 quite the opposite of those of the front of ^he 
 storm. In front the clouds appear generally 
 stratified but in the rear they are generally 
 cumuli with a clear blue sky above. Cirrus clouds 
 do not often appear in the rear of the cyclone. 
 The "mare's tails" and long wispy cirri often 
 appear to the south of the center and indicate 
 wind rather than rain. 
 
 The corona is formed by the diffraction of sun- 
 light usually in alto-stratus cloud which is at an 
 altitude between two and three mUes. The corona 
 exhibits the colors of the rainbow with blue inside 
 and red outside. If conditions are right, a corona 
 will be seen in advance of the cyclone. The halo 
 is a phenomenon of the ice crystals of the cirro- 
 stratus ordinarily at twice the elevation of the 
 alto-stratus. It usually is followed by rain within 
 twenty-four hours. A corona may be formed 
 when any thin cloud of water particles passes be- 
 tween the observer and the sun or moon. Ap- 
 parently the smaller the particles of the cloud, 
 
WEATHER AND THE SKY 219 
 
 the larger the corona, consequently, if the diam- 
 eter of the corona rapidly grows smaller and the 
 clouds denser, the storm is rapidly approaching. 
 Mock-suns or mock-moons are caused by the inter- 
 section of halos and are merely brighter spots 
 due to the reinforcement of one halo at this point 
 by the brightness of the intersecting halo. Some- 
 times the halos are too faint to be seen, but the 
 mock-suns or sun-dogs may be visible. 
 
 The anticyclone is in many respects the antith- 
 esis of the cyclone. It is the system surround- 
 ing a barometric "high" and the air is cahn and 
 cold in this central region. In the outskirts the 
 wind blows clockwise around the center and 
 spirally outward as seen in an imaginary bird's- 
 eye view as on a weather map. The direction of 
 the air-currents is such as to bring the cold air 
 from high altitudes down to the surface of the 
 earth, hence, the regions of "highs" are cooler 
 than "lows." The anticyclone is often compara- 
 tively stationary for many days while the cyclone 
 generally moves steadily and sometimes fairly 
 rapidly. It is characterized by blue sky with, of 
 course, fair-weather cumulus clouds, by much 
 dew, and often by a hazy horizon, and by mists 
 in the valleys during the night and early morning. 
 No dew after a hot day often foretells rain ap- 
 proaching. 
 
 Fleecy cirro-cumulus are often formed near the 
 edges of anticyclones and under these conditions 
 foretell fair weather. 
 
220 THE BOOK OF THE SKY 
 
 "If woolly fleeces spread the heavenly way 
 No rain, be sure, disturbs the summer's day." 
 
 They are sometimes formed before thunder- 
 storms and under such circumstances, they would 
 not be fair-weather clouds. When occurring in 
 large numbers they form the "mackerel" or 
 "curdled" sky. In weather-lore there is some 
 conflict in regard to the portent of these clouds, 
 but mackerel skies are usually considered to por- 
 tend approaching rain. 
 
 "Mackerel scales and mare's tails 
 Make lofty ships carry low sails." 
 
 Perhaps it is safe to state that no cyclonic foul 
 weather is indicated by wooUy cirro-cumuli. If 
 a mackerel sky is followed by a general thicken- 
 ing, precipitation is usually only a few hours dis- 
 tant, but if the scales diminish in size and disap- 
 pear, or nearly so, dry weather is generally as- 
 sured. Cirro-cumuli sometimes develop into 
 strato-cumuii, but despite the general suspicion 
 with which stratus clouds should be viewed, 
 strato-cumuii do not bring precipitation. 
 
 Clouds may appear very dark and foreboding 
 but as long as they are broken, there will be little 
 or no precipitation. This darkness is caused by 
 the great thickness through which little of the 
 sunlight illuminating their upper surfaces is able 
 to penetrate. "When these coalesce into a uniform 
 
WEATHER AND THE SKY 221 
 
 sheet and grow gray, rain or snow is usually ap- 
 proaching. Little need be said of the nimbus 
 clouds because rain or snow is falling from them 
 and the weather is obvious. If the sky is lighter 
 beyond them, the rain or snow is likely to be of 
 short duration. 
 
 Local weather conditions are quite varied 
 owing to local influences but sky-signs are 
 usually plentiful and reliable. However, the de- 
 tails of such weather may be best studied by 
 observation fortified by a knowledge of the details 
 of general storms. This phase of weather be- 
 comes exceedingly obvious to the aerial traveler. 
 For example, during a dry spell when there is not 
 enough moisture in the air from which cumulus 
 clouds may form over wide areas, it is not tmusual 
 to look down upon clouds floating over woods, 
 river valleys, and swampy regions with no clouds 
 appearing elsewhere. The local variations of 
 weather conditions and of the appearance of 
 clouds very soon impress the observant cross- 
 country traveler in cloudland. The details of 
 local conditions cannot be adequately discussed 
 within the boundaries of a single chapter, there- 
 fore, they will be left to each interested reader 
 to observe and to analyze in his own locality. It 
 should be noted that local variations are usually 
 merely a matter of intensity and that principles 
 remain fairly definite and universal over the 
 entire globe. Superposed on the general and local 
 storms or weather, there are always the diurnal 
 
222 THE BOOK OF THE SKY 
 
 weather conditions. Today one of these may- 
 dominate, tomorrow, another, but local or diurnal 
 conditions can hardly convert the foul-weather 
 cirrus into the fair-weather cumulus clouds. 
 
 The sky displays the effects of the seasons. 
 During dry weather months in some regions only 
 blue sky is seen in the rear of a cyclone because 
 there is not enough moisture to form cumuli ; how- 
 ever, in damp localities the cumuli may be formed 
 in all seasons, though they may be denser in 
 summer than in winter. It is perhaps commonly 
 observed that similar weather is experienced 
 about the same time every year. This does not 
 appear strange when the seasonal variation of 
 winds, for example, is considered. In fact, the 
 word "monsoon" is derived from an Arabic word 
 meaning "season." However, the seasonal vari- 
 ation of weather is not sufficiently alike from year 
 to year to warrant the compilation of daily 
 weather charts and prognostics a year in advance. 
 Furthermore, there are stiU too many complex 
 influences which are not thoroughly correlated at 
 present, to trust a year in advance to statistical 
 averages. Possibly in the distant future the mete- 
 orological web win be so completely untangled 
 that the weather may be prophesied a year in 
 advance, but a day or two is the safe limit at pres- 
 ent. In fact, these are further reasons for observ- 
 ing the sky-signs from day to day; furthermore, 
 the sky foretells weather sometimes in advance 
 of the Ibarometer. 
 
WEATHER AND THE SKY 22S 
 
 In the doldrums, where calms may endure for 
 weeks, the sky is of a hazy white color, occasion- 
 ally becoming uniformly gloomy but remaining 
 cloudless. At other times small patches of cumuli 
 appear. In the trades the sky is usually strewn 
 with small detached cumuli floating high. 
 
 A complete discussion of the relation of sky- 
 signs to the weather would be extensive and could 
 not be presented without extensive tedious quali- 
 fications, therefore in the foregoing paragraphs 
 some general aspects have been discussed. The 
 reader who is already interested or who plans to 
 absorb some of the interest in the sky, whether 
 from the earthly world or the aerial one, wiU find 
 it easy to obtain much experience in reading the 
 sky-signs as a by-product of his observations. The 
 clouds cannot alone be depended upon always. 
 Their origin and meaning, however, are usually 
 evident if preceding weather and conditions of the 
 sky have been noted. These combined observa- 
 tions will aid in developing accuracy in weather 
 forecasting. By all means, the beginner should 
 observe daily if possible the charts issued by the 
 Weather Bureau. These, reinforced by observa- 
 tions of the sky, will make for proficiency. This 
 aspect of the sky as well as the others treated in 
 various chapters supply just so much more of 
 interest along the highway of life. 
 
 A few brief statements, devoid of their quali- 
 fications, which would be tedious to read, may be 
 of interest. 
 
THE BOOK OF THE SKY 
 
 Cumulus clouds are likely to be fair-weather 
 clouds if they are small, harsh, and high. When 
 they grow large and dark, showers should not 
 come as a surprise. 
 
 "When clouds appear like rocks and towers 
 The earth's refreshed by frequent showers." 
 
 If huge ranges of ctunuli lie beyond in the di- 
 rection of the wind, a heavy storm is probable. 
 
 The details of the thunderstorm have been pre- 
 sented in other chapters. 
 
 When clouds of various levels are moving in 
 different directions there is obviously an unset- 
 tled state. Eain or snow may follow but often 
 this is a condition preceding the close of a cyclonic 
 storm. 
 
 Huge cumulus clouds against a blue sky some- 
 times in winter are responsible for snow flurries 
 after which a period of clear cold weather sets in. 
 
 Turbulent clouds obviously indicate violent 
 gusty winds, and squalls may be looked for in 
 proper season. 
 
 Cloudy nights are warmer than clear ones. 
 
 The cloudless sky will yield various signs to 
 the experienced observer. Its color and haziness 
 in conjunction with the preceding clouds and 
 other conditions should be observed and the re- 
 sulting weather noted. 
 
 Continued fair weather generally follows: if 
 cumulus clouds decrease toward evening ; if cirrus 
 
WEATHER AND THE SKY 225 
 
 clouds disappear; if clouds rise on mountains; 
 if the sun sets in a cloudless sky; if myriads of 
 stars are visible; if the wind is gentle and west- 
 erly. 
 
 "A rainbow in the morning 
 Is the shepherd's warning; 
 But a rainbow at night 
 Is the shepherd's delight." 
 
 In the former case there is a bank of cloud and 
 rain to the west, but in the latter case the sun 
 has broken through and indicates a clearing. 
 
 Foul weather is generally approaching: if 
 cirrus clouds appear well-defined and extend 
 across the sky from the west; if cirrus develop 
 into cirro-stratus clouds; if scuds are drifting 
 from east to west; if a ring surrounds sun or 
 moon; if stars are indistinct; if clouds gather or 
 lower upon mountain peaks ; if the sun is gradu- 
 ally obscured by clouds. 
 
 There will be precipitation: shortly after 
 cumulus clouds darken and show trailing showers ; 
 several hours after the sun or moon has been 
 blotted out by cirro-stratus ; in from ten to thirty 
 hours after the first foul- weather cirri appear; 
 shortly after a thunder-cloud appears on the west 
 wind ; an hour or more after a thunder-cloud ap- 
 pears with an east or southeast wind. 
 
 There will be a clearing if the clouds rise and 
 break up and the wind shifts toward the west. 
 
THE BOOK OP THE SKY 
 
 The temperature will decrease if the sky clears 
 up toward nightfall. 
 
 Of course, winds play a dominating part in the 
 weather and in weather forecasting. Their course 
 is determined by the direction in which the clouds 
 are moving with more certainty generally than at 
 the surface of the earth. Westerly winds mean 
 fair weather ; a shift to the south or to the north- 
 east indicates the approach of foul weather; a 
 shift from easterly to westerly indicates a clear- 
 ing. 
 
 At best, the foregoing is only a brief introduc- 
 tion to the extensive phase of the sky as a weather- 
 indicator, but it should be helpful to the earthly 
 observer and to the aerial traveler if he wishes to 
 become weather-wise. Those who are content to 
 be admirers of the sky without considering its 
 utility may find that a general appreciation of 
 the utility of the sky may intensify its beauty as 
 well. 
 
CHAPTER XXI 
 
 THE CONVOY 
 
 "And when the stream. 
 Which overflowed the soul had passed away, 
 A consciousness remained that it had left, 
 Deposited upon the silent shore 
 Of memory, images and precious thoughts, 
 That shall not die, and cannot he destroyed." 
 
 — ^WOEDSWORTH. 
 
 GLOTJDLAND is versatile. It is a fairyland 
 of beauties and wonders wMcli awaken ad- 
 miration and awe. It is a dreamland of inspiring 
 panoramas and awesome spectacles which, chal- 
 lenge the senses. It is moody and reflects the 
 intent and action of Nature. It has enslaved 
 poets of all ages and its infinitude lends wings to 
 the imagination. It has helped to make this globe 
 inhabitable by bringing rain and by screening the 
 earth from the burning rays of the untempered 
 sun of space. All these functions it has performed 
 unasked, unaided, and uncontrolled until, in gen- 
 eral, man in his growing independence has be- 
 come indifferent to its beauty, its wonders, and 
 even its utility. 
 
 227 
 
228 THE BOOK OF THE SKY 
 
 But cloudland has become a Hghway of travel, 
 and as man takes to the air the novelty will set 
 his senses keenly alert. His nascent condition 
 may give clondland its great opportunity for 
 captivating his interest and admiration. Aerial 
 travel is a superb achievement which has ex- 
 panded the world and the experiences which it 
 affords will not be quickly exhausted. However, 
 they will not be adequately described untU poets 
 have flown for ages through cloudland. 
 
 With all that is ahead it may seem unnecessary 
 to look back; still certain cherished memories 
 linger behind which wiU always glow despite the 
 experiences to come. And the immortal glow of 
 a cherished memory so often colors the experi- 
 ences and gives to them a fuller significance. In 
 this little volume the recent war has not been 
 mentioned except to credit it with vastly hasten- 
 ing the realization of man's mastery of the air. 
 An attempt has been made to describe the delights 
 of air-travel and the facts of the aerial world as 
 they wiU always be. 
 
 During the war numberless aerial experiences 
 were accumulated. Most of them were colored by 
 the awfulness of warfare. Men braved the dan- 
 gers of the air at the front, fought gallantly and 
 unselfishly, and performed wonderful deeds 
 worthy of high places in the traditions of the 
 peoples for whom they fought. But such deeds 
 are for the annals of war. Worthy as they are, 
 they have no logical place in this little volume. 
 
THE CONVOY 229 
 
 Still the mastery of the air donbtless will be as- 
 sociated for many years to come with the terrible 
 strife which developed the airplane so rapidly 
 from a doubtful infancy to its present confident 
 and successful youth. War is a bloody blot which 
 should be forgotten but its lessons should be re- 
 membered and the memory of its victims and 
 heroes should be reverently cherished. 
 
 The glory won by aircraft in war has been ade- 
 quately recorded in the annals of the recent con- 
 flict but it is difficult to close without adding a 
 note reminiscent of the service which aircraft 
 have rendered and of their meteoric development. 
 A certain event appears to supply this note with- 
 out introducing the terrible side of warfare. 
 Furthermore, this event has a broader signifi- 
 cance, for it not only pictures the remarkable 
 development of the airplane from a hazardous 
 plaything to a mighty conqueror of the air but it 
 also symbolizes a nation unified in its imselfish 
 mission. 
 
 It was a midsummer's morning on the Atlantic 
 coast and those who were abroad on the bay at 
 daybreak saw many dim shadowy hulks outlined 
 in the dawn against the brightening sky over the 
 watery horizon framed in the gateway to the 
 ocean. Several hours later at the naval air-sta- 
 tion the usual routine activity was augmented, but 
 owing to the nature of the business at hand, a 
 knowledge of it reposed only in the minds of a 
 few superior officers. Two gigantic flying-boats 
 
230 THE BOOK OF THE SKY 
 
 were roaring eagerly as they were being warmed 
 up for their continuous all-day patrol. They 
 weighed many tons and the spread of their wings 
 dwarfed all ordinary airplanes into insignificant 
 pigmies. Fuel by the ton was being poured into 
 their depths. They bristled with the accoutre- 
 ments of war and the crew of six men was com- 
 fortably quartered with room for many more. 
 These huge flying-machines with a cruising range 
 of a thousand mUes and a net lifting force of sev- 
 eral tons, had evolved under the stress of war 
 from the weakest infancy in less than four years. 
 As they roared in their majestic confidence amid 
 their surroundings, which bore aU the earmarks 
 of hurried construction, they symbolized the 
 power of knowledge if commandeered and di- 
 rected to the utmost. 
 
 Suddenly the impatient roar of the motors 
 diminished and one of the huge craft slid easily 
 into the water to ride the gentle swells with purr- 
 ing motors suggestive of a contented water-fowl. A 
 few moments later its mate took to the water with 
 the same air of satisfaction. After a little ma- 
 neuvering everything seemed to be in readiness 
 for the pair to start on an aerial cruise which, 
 barring mishaps, would be at least an eight-hour 
 patrol. The motors of one of them increased to 
 a terrific roar as the craft gained speed down the 
 great harbor. It showered spray as it plowed 
 through the surface of the water. The white 
 ispray grew less as the depth of the furrow de- 
 
THE CONVOY 231 
 
 creased and soon the forward observer became 
 conscious that the surface of the water was reced- 
 ing downward. Straight for a battleship the huge 
 craft flew as though bent on a mission of destruc- 
 tion, but the grotesquely painted man-of-war 
 passed underneath by a safe margin. 
 
 How intimate one felt with the vessels glisten- 
 ing upon the water below! "With a safe landing 
 surface on all sides the crew of a flying-boat may 
 be intimate with the water's surface, but not so 
 for those who fly over the harbor in airplanes. 
 An occasional dip in an airplane in order to pass 
 close to the bow or stern of a cruiser and to wave 
 to the "jackies" is a thrilling and suspended 
 moment for the occupant of an airplane. But this 
 huge flying-boat with wings spread considerably 
 more than a hundred feet, was intimate with the 
 vessels because it is as much at home on water as 
 in the air. Describing a huge arc this super-air- 
 craft made for the bay and once over the bay it 
 curved again toward the gateway to the ocean 
 twenty miles away. 
 
 At an altitude of a few hundred feet in a stable 
 flying-boat one enjoys comforts not afforded in 
 the small high-flying airplanes. Besides, there is 
 novelty in the security of this low altitude in a 
 flying-boat because airplanes must go high for 
 safety. At an altitude of a thousand feet or more 
 the details of the harbor, the bay, and the gate- 
 way to the ocean are visible for many miles. 
 Steadily the coast-line draws near and the mine- 
 
THE BOOK OF THE SKY 
 
 sweepers and patrol boats are seen on duty at the 
 gateway. Passing over this junction of ocean and 
 its inland arm, the details of the submarine net 
 are visible below. 
 
 The huge aircraft is now over the dark blue- 
 green Atlantic Ocean and heads for the eastern 
 horizon. As the observer notes the coast-Une 
 being left behind at the rate of seventy-five knots 
 per hour, he turns unconsciously to look back for 
 the mate of the craft. There it comes, on the 
 same course, a smaU speck to the west. Down 
 below on. one side is a tramp schooner with bril- 
 liant white sails distended in a fine breeze. On 
 the other side four small freighters are abreast. 
 "In company there is strength" seems to be the 
 motto in the waters below, for submarines are 
 abroad in this region where the highways of the 
 sea converge. Are those smaU cigar-shaped ob- 
 jects sharks? They must be, for the sharks are 
 in this region this summer. 
 
 The observer in the prow pf this huge flying- 
 boat is busy, for there is so much to see and to 
 feel. All about him above and below, there is 
 much of interest, for up to this time few persons 
 have been abroad in this aerial world over the 
 Atlantic and headed east for a day's cruise for 
 the most part out of sight of land. He looks back 
 in admiration upon the mechanism weighing sev- 
 eral tons which not only supports itself by its 
 own power but carries him and several tons of 
 men and equipment. As he looks backward he 
 
THE CONVOY 283 
 
 sees a pair of heads projecting above the curved 
 back of the hull. They are the stalwart pilots 
 who guide the craft. Still farther back, perhaps 
 thirty feet, is a cabin from which huge wings 
 spread laterally. Out upon one of these wings 
 stands a human being with leg twisted round a 
 strut, tinkering with a piece of the mechanism. 
 
 During this time the craft has curved in a great 
 arc and the observer is suddenly surprised to see 
 the craft's mate come alongside. They cruise 
 side by side for some time, then the mate veers 
 off as if bent upon some mission. As it dwindles 
 in the distance the observer seats himself in the 
 cockpit out of the terrific wind and reflects upon 
 the wonders of flying. In his notebook he jots 
 down the things he has seen and attempts to de- 
 scribe his feelings. The situation impresses him 
 with the same unreality that he felt in the polar 
 regions four miles above or far out on the aerial 
 highway in a cross-country flight. 
 
 Minutes pass as his psychological being tries 
 to digest and to assimilate the impressions of the 
 past half-hour. Down in this cock-pit with only 
 the sky visible of all the infinitude of space and 
 area which surrounds him, his thoughts wander 
 back a score of years to the advent of the first 
 automobile. Then back a century to the first 
 steamboat and then to the intrepid explorer who 
 sailed out from the east to discover the continent 
 which is now disappearing in the western haze. 
 In the course of a few moments his thoughts scan 
 
234 THE BOOK OF THE SKY 
 
 the entire development of travel and he sees in 
 Ms mind's eye the epochal achievements of the 
 past. But how progress has accelerated until 
 achievements have become massed in the present 
 century! Surely it is wonderful to live in this 
 age of accumulated and directed knowledge. 
 
 But he may reminisce at home without wasting 
 wonderful opportunities of a life-time. He rises 
 to mount his high perch whence his gaze may span 
 almost the entire circle of the horizon. He 
 glances downward over the nose of the craft and 
 becomes transfixed. Down there upon that ruffled 
 blue-green area is a group of more than a score 
 of vessels. They are orderly, grim, and bent upon 
 a purpose. Ahead is the zigzag white wake of the 
 destroyer in the lead. Beyond the outskirts are 
 the busy little submarine chasers. The observer 
 now accounts for the ghostly forms which he saw 
 toward the east at dawn. They comprised this 
 convoy bound for the sea and Europe. 
 
 As the huge craft dips downward toward this 
 group of vessels, khaH-clad beings turn their 
 faces upward and wave their caps. To them this 
 crew on wings is a guardian angel whose watchful 
 and penetrating eyes look for the submerged 
 enemy. To the observer this group of silent, grim, 
 speeding vessels with its cargo of men, food, and 
 munitions is the answer of a nation which loves 
 freedom and whose purpose is to aid others 
 against the tyranny of aggression. 
 
 The aircraft soars over and beyond for several 
 
THE CONVOY 235 
 
 miles, then in ahnge circle it sweeps tlie ocean for 
 many miles. Its mate is patrolling a similar area 
 ahead and on the other side. Each hour a circle is 
 described and the aircraft returns to the convoy. 
 
 "With each bird's-eye view of the convoy steadily 
 steaming eastward in an orderly manner bespeak- 
 ing a grimness of purpose, the observer's feelings 
 become more definite and vivid. With each inter- 
 yening hour for reflection the great significance of 
 this group of vessels becomes clearer. They sym- 
 bolize a nation's unity, its strength, its determina- 
 tion, its grimness of purpose. 
 
 All day long the huge aircraft circles far and 
 wide and with each successive return to the group 
 of vessels so tiny upon the vast ocean down below, 
 the convoy is ten miles farther upon its eastward 
 course. The day passes and the sun is low in the 
 west. The aircraft does not head out again in ad- 
 vance of the convoy but circling over it as if reluc- 
 tant to leave, it finally turns its prow toward the 
 sunset and home. It seems cruel to desert that 
 silent determined group, but Night will soon 
 drop its protecting curtain. 
 
 To the west the sun is sinking low upon the 
 watery horizon, for the coast lies beyond the curve 
 of the earth, an hour's flight away. The observer 
 looks back upon the group of vessels rapidly 
 diminishing in the distance. He longs for ade- 
 quate words for his notebook and wishes that a 
 poet might have witnessed the inspiring sight. 
 
THE BOOK OF THE SKY 
 
 Surely only a poet could do justi9e to the symbol- 
 ism of that convoy. 
 
 As the aircraft roars toward the west the hori- 
 zon becomes a roughened line of land cutting the 
 red disk of the sun as it sinks to rest. The sunset 
 is tinged with the sadness of a double farewell — 
 one to Day and one to that group of vessels dis- 
 appearing into the night at the eastern horizon. 
 For the observer, twilight's curtain is closing the 
 fullest day of his life. The hollowness and in- 
 adequacy of words mock him as he reads these 
 (lines in his notebook, — 
 
 THE CONVOY 
 
 Par below, furrowing the sea, 
 
 A score of ships with purpose grim 
 
 Sent forth to curb War's cruel whim, 
 
 You symbolize our unity. 
 
 To enemy of liberty 
 
 You bear the cup filled to its brim 
 
 With dark despair. Our eyes grow dim: 
 
 With pride as you steam eastwardly. 
 
 We soar above and watch below 
 With eyes which pierce with greater sight 
 The depths where lurk determined foe. 
 But tired wings must soon alight. 
 Godspeed ! We turn toward sunset glow 
 While you steam on into the night.