Qass. 
 Book. 
 
 COPYRIGHT DEPOSIT 
 
THE 
 
 NAVIGATOR'S POCKET-BOOK 
 
THE 
 
 NAVIGATOR'S POCKET-BOOK 
 
 ffilleD witb pure <3olD 
 
 ARRANGED FOR IMMEDIATE REFERENCE TO ANY 
 NAVIGATION SUBJECT 
 
 A Complete Guide and Instructor for the Navigator, containing Four 
 Hundred Exhaustive Definitions in Addition to all the Practical Rules 
 for Working Middle Latitude, Mercator's and Great Circle 
 Sailings, as well as Finding the Ship's Place by Nu- 
 merous Chart Considerations, and the Latitude and 
 Longitude by Dead Reckoning, and by the 
 Sun, Moon, Planets, and Stars 
 
 ACCORDING TO SHORT, SIMPLE, AND RELIABLE METHODS 
 
 Also the Arithmetic of Angular and Time Measure 
 Compass Deviation, Nautical Astronomy 
 
 Treatise on the Instruments of Navigation 
 
 Law of Storms, Keeping the Log Book 
 
 Magnetism. Logarithms, Measuring Altitudes 
 
 Sumner's Method, Time, Weather, etc., etc. 
 
 TOGETHER WITH DANGER- ANGLE AND OTHER TABLES 
 BY ,/ 
 
 CAPTAIN HOWAKD ^ATTERSON 
 
 Formerly Professor of Naval Science at Brown's College, Principal of The New 
 York Navigation School, and Commandant of the Haytien Navy 
 
 AUTHOR OF 
 
 "The Yachtsman's Guide,'" "Hand-book for Masters and ^M&be$? l ~ Xi Y&chting 
 Under American Statute," " The Illustrated Nautical Dictionary," etc., etc. 
 
 MUN i t*M 
 
 NEW YORK 
 
 CHARLES SCRIBNER'S 
 1894 
 
 HjZ/ 
 
y 
 
 COPYRIGHT, 1894, BY 
 
 CHARLES SCRIBNERS SONS 
 
 7<? ■■■'; 
 
 TROW DIRECTORY 
 
 PRINTING AND BOOKBINDING COMPANY 
 
 NEW YORK 
 
CHESTER W. CHAPIN, ESQ. 
 Corinthian Yachtsman 
 
 Steady at the helm from whatever quarter comes the wind 
 Quick to catch either the caressing or threatening whisperings of the sea 
 And novice in nothing that makes a sailor of the highest and truest 
 American type 
 
 THIS BOOK IS RESPECTFULLY DEDICATED 
 BY HIS FRIEND 
 
 THE AUTHOR 
 
PREFACE 
 
 There are many voluminous and bewildering works on the 
 subject of navigation, but up to the present time there has not 
 existed a series of short, simple laws founded on correct princi- 
 ples and expressed in homely language, whereby the navigator 
 might quickly develop his position under various conditions at 
 sea and along shore. In this little volume has been incorpo- 
 rated every practical formula for determining the latitude and 
 longitude by dead reckoning and by solar, lunar, and stellar 
 observations, as well as concise and lucid directions for chart- 
 work, the various sailings, and for accurately fixing the ship's 
 place when in sight of land, and in every consideration the 
 author has succeeded in simplifying and abridging the confus- 
 ing and tedious rules and methods in common use. The purely 
 original arrangement of this pocket edition of common-sense 
 navigation contributes generously to its value, as it affords means 
 of immediate recourse to any and every subject within the 
 sphere of the practical navigator. The problems are all worked 
 according to Bowditch's American Nautical Tables, which may 
 be purchased from any book-dealer for $1.25, but it is to 
 be explained that the numbers called for in the text may be 
 
Vlll PREFACE 
 
 changed to apply to other navigation tables. In no particular 
 lias it been attempted to go beyond the limits of honest, service- 
 able navigation as practised at* sea, consequently the reader 
 would seek in vain for fancy or abstruse sailings and irrelevant 
 definitions. 
 
 H. P. 
 New York, 1894. 
 
THE NAVIGATOR'S POCKET-BOOK 
 
 A. M. — Ante Meridiem ; before meridian ; embraces the 
 twelve hours from midnight to noon. 
 
 ABOVE THE POLE.— When the north star is situated so 
 that it is intercepted between the observer and the pole, it is said 
 to be above the pole. This applies to other circumpolar bodies. 
 (See Upper Transit.) 
 
 ADJUSTING SCREWS.-(See Sextant.) 
 
 ADJUSTMENT. — The correction of a compass for deviation 
 by the employment of magnets, or the regulation of the mirrors 
 of a sextant. (See Compass Adjusting ; Sextant.) 
 
 ALIDADE. — An instrument for taking bearings, consisting 
 of two arms revolving around a circular brass plate or dial 
 marked with the points and degrees of the compass. It is 
 secured on top of the binnacle hood and set to the ship's 
 course, so that any bearing given by it will represent the mag- 
 netic bearing as by the compass beneath. (See Azimuth 
 Attachment ; Pelorus.) 
 
 ALMANAC. — A nautical calendar in which is tabulated for 
 the various days of the month, the declinations of the sun, 
 moon, planets and stars ; their right ascensions ; the equation of 
 time, etc. 
 
2 THE NAVIGATOR'S POCKET-BOOK 
 
 ALTITUDE.— The angular height of a body above the 
 horizon. 
 
 Remarks Concerning Meridian Altitudes. — The term me- 
 ridian altitude means the highest point attained by a heavenly 
 body above the observer's horizon, which is secured when the 
 object bears either true north or south as the case may be. 
 When the observer is north of the body's declination it will be 
 observed to the south, but when the observer is south of the 
 body's declination its image will be thrown to the northern 
 horizon. 
 
 By mentally adding four minutes of time to the face of the 
 ship's clock for every degree of longitude sailed east since the 
 clock was last set, or subtracting four minutes for every degree 
 sailed west, the observer will be enabled to anticipate the time 
 of the meridian passage and be prepared to observe the same. 
 
 There are two methods employed for bringing the image of a 
 heavenly body to the horizon at the time of the meridian pas- 
 sage, the first of which is as follows : 
 
 Make the vernier and arc zeros cut one another, then, in the 
 case of the sun, turn down the shade-glasses to suit the eye ; 
 point the telescope toward the body so that its colored image is 
 seen in the horizon-glass ; now advance the sliding limb, and in 
 proportion as it is moved along the arc, bring the sextant to the 
 vertical — otherwise the image would disappear from the horizon- 
 glass. 
 
 The second method practised oftentimes at sea for the me- 
 ridian observation is to anticipate the approximate altitude 
 and to set the same on the sextant, then to direct the telescope 
 to that part of the horizon which is beneath the body, making a 
 perfect contact by the aid of the tangent screw. This latter 
 method obviates the necessity of " shooting the heavens" and 
 
THE XAVIGATOR S POCKET-BOOK o 
 
 insures against blinding from the dazzling effects of the sun 
 •when caught in the unsilvered part of the horizon-glass. To 
 calculate the approximate altitude, proceed as follows : 
 
 When the latitude by dead-reckoning and the declination of 
 the body are of the same name, subtract them from one another, 
 then subtract the remainder from 90° — the answer will be the 
 approximate altitude. 
 
 When the latitude by dead-reckoning and the declination of 
 the body are of contrary names, add them together, then sub- 
 tract their sum from 90° — the answer will be the approximate 
 altitude. 
 
 A meridian altitude will always be some part of 90°— an arc 
 from the horizon to the point directly over the head of the ob- 
 server, called the zenith. This arc is always a quadrant (90°), 
 and what an altitude lacks of 90° is always the zenith distance. 
 
 Meridian Altitude of the Sun.— Considering that the sun's 
 image has been brought almost in contact with the horizon, 
 proceed to make a perfect contact by the aid of the tangent 
 screw, fingering the same until the sun's lower limb is just kiss- 
 ing the horizon line. The vertical movement of this luminary 
 is very slow when approaching the meridian, and within several 
 minutes of noon on each side of that point its motion is imper- 
 ceptible. Until, however, the body is almost on the observer's 
 meridian its limb will show a slow but steady lifting above the 
 horizon, and must be brought down when it shows daylight be- 
 tween it and that part of the horizon which is directly beneath. 
 The idea is to secure the highest altitude which the sun offers. 
 
 In order to be positive of the proper place of contact, the 
 navigator should oscillate (swing) the instrument while keeping 
 the eye to the telescope, so that the sun's image will appear to 
 describe the lower segment of a circle, the lowest point of 
 
4 THE NAVIGATOR'S POCKET-BOOK 
 
 which will be the horizon directly beneath the sun, and to 
 which point the limb of the sun must be brought in contact. 
 
 As soon as it is decided that the sun is done rising, call " eight 
 bells ! " The hands of the ship's clock will then be set at twelve, 
 as the apparent or sun time at the ship. Although twelve 
 o'clock has been " made " at ship, do not consider the observa- 
 tion finished until the image of the sun's limb is seen to dip 
 below the horizon line ; but when this is observed, under no 
 circumstances bring the sun's limb up to the line of the horizon, 
 as the dipping of the limb proves that the body has crossed over 
 the highest point of the great circle which it describes from 
 rising to setting ; and it is from this highest altitude that we 
 must calculate the ship's distance from the equator by the appli- 
 cation of the declination. 
 
 In relation to the use of the upper and lower limbs of the sun 
 when observing its altitude, it will be found that the lower 
 limb will afford the most satisfactory result, as a daylight line 
 may be distinguished between it and the horizon : whereas the 
 sinking of the upper limb to the horizon is attended with danger 
 of inaccuracy. (See Latitude.) 
 
 Ex. Meridian Altitude of the Sun. — This altitude is meas- 
 ured by simply bringing the sun's image down to that part of the 
 horizon line that is directly beneath the body, proving the point 
 of contact by the oscillation of the sextant. Without further 
 consideration or delay the measured altitude is accepted and read. 
 
 Time Altitude of the Sun. — When observing an altitude of 
 the sun for finding the longitude by a chronometer sight or by 
 equal altitudes, simply throw the sun's image to that part of the 
 horizon which is directly beneath the body, proving the point of 
 contact by oscillating the sextant, and at the instant of proper 
 contact note the Greenwich hour, minute, and second shown 
 
THE NAVIGATOR'S POCKET-BOOK 5 
 
 by the chronometer. This may be done by having some one 
 stationed by the time-piece, who will make a memorandum of 
 the time when so directed by the navigator calling "time" 
 when he brings the sun's limb in perfect contact, or it may also 
 be done by the navigator himself having a hack watch set to 
 Greenwich time which he holds in the hollow of his left hand, 
 with its face toward him, so that it is in plain view while 
 measuring the altitude. (See Longitude.) 
 
 Altitudes in Foggy Weather. — When, owing to light fog or 
 mist, the radius of the visible horizon is only two or three miles, 
 get the eye as near to the surface of the water as possible when 
 measuring the altitude of a heavenly body, and by this means 
 the horizon may often be brought within the fog-described 
 circle. Should the fog be heavy, it may be possible to get above 
 it by going aloft. When this can be accomplished a good obser- 
 vation is obtainable. 
 
 Altitudes in Cloudy Weather. — When the mass of the sun 
 or moon is visible, but the limbs ill-defined in consequence of an 
 overcast sky or the body shining through a rain-cloud or light 
 fog, the image of the mass may be brought down and the centre 
 of this ball of light calculated and allowed to be cut by the 
 horizon line. In this case no allowance is to be made for 
 semi-diameter. The ship's position, determined by this method, 
 will probably be a little in error, but as a makeshift the rule has 
 its value. 
 
 Meridian Altitude of the Moon. — The astronomical mean 
 time of the moon's meridian passage is given in the nautical 
 almanac for everyday of the month at Greenwich, and this time 
 answers, within a few minutes, for all longitudes. Proceed to 
 observe the altitude in the same manner as explained for the sun, 
 but use no shade-glasses. If the horns of the moon are down it 
 
6 THE NAVIGATOR'S POCKET-BOOK 
 
 will be necessary to measure the altitude of the upper limb ; but 
 if the horns are up the lower limb will be measured. When the 
 moon is full, or nearly so, measure the lower limb always in 
 preference to the upper limb. (See Latitude.) 
 
 Time Altitude of the Moon. — This is observed in exactly the 
 same manner as described for a time altitude of the sun, omit- 
 ting the shade glasses and having regard to the upper and lower 
 limbs as explained in Meridian Altitude of the Moon. (See 
 Longitude.) 
 
 Meridian Altitude of a Planet. — The astronomical mean 
 times of the meridian passages of the planets are given in the 
 nautical almanac for every day of the month, and apply prac- 
 tically to all longitudes. Proceed in precisely the same way as 
 explained for a meridian sight of the sun, but use no shade- 
 glasses and do not take the semi-diameter into consideration. 
 (See Latitude.) 
 
 Time Altitude of a Planet. — This is observed in exactly the 
 same manner as described for a time altitude of the sun, omit- 
 ting, of course, the shade-glasses. (See Longitude.) 
 
 Meridian Altitude of a Star. — The following method of ap- 
 proximating the star's altitude and placing the same on the sex- 
 tant should be observed, as it insures against bringing down the 
 wrong body : 
 
 When the latitude by dead-reckoning and the star's declina- 
 tion are of the same name, subtract them from one another, then 
 subtract the remainder from 90°— the answer will be the rough 
 altitude; but when the latitude by dead-reckoning and the 
 star's declination are of contrary names, add them together and 
 subtract their sum from 90° — the answer will be the rough 
 altitude. 
 
 A few minutes before the time given in the star tables (in the 
 
THE NAVIGATOR'S POCKET-BOOK 7 
 
 back of this volume) for the meridian passage, set the sextant, 
 direct it either to the north or south horizons, according to the 
 latitude of the ship and the declination of the body, and the 
 star's image will be seen in the horizon-glass of the instrument ; 
 then make a perfect contact by the aid of the tangent screw, and 
 wait for the star to reach its highest point, proceeding in the 
 same manner as described for a meridian observation of the sun, 
 it being understood that shade-glasses are not employed. 
 
 The declination of the star as compared with the latitude of 
 the ship will always dictate the direction (north or south) in 
 which to look for the horizon beneath the body. If the star's 
 declination is north of the ship's position, the northern horizon 
 will be used, but if the star's declination is south of the ship's 
 position, the southern horizon will be used. 
 
 Dawn and twilight afford the best horizons for star observa- 
 tions. (See Latitude.) 
 
 Time Altitude of a Star. — This is observed in the same man- 
 ner as described for a time altitude of the sun, only without 
 making use of the shade-glasses. It is to be explained, how- 
 ever, that until the navigator has studied the heavens and be- 
 come sufficiently familiar with them to locate the nautical stars 
 when they are off the meridian, this method of finding the 
 longitude cannot be employed by him. The superior size and 
 brilliancy of the planets will always prove an unfailing guide 
 when desiring to select one of those bodies, but confusion will 
 at once arise in seeking to fix upon particular stars unless the 
 observer is acquainted with their relative places. (See Fixed 
 Stars ; Longitude.) 
 
 Altitude of the Pole Star.— Simply throw the star's image to 
 that part of the horizon which is directly beneath the body, 
 proving the point of contact by oscillating the sextant, and note 
 
8 THE NAVIGATOR'S POCKET-BOOK 
 
 the local apparent time at ship as shown by the clock. (See 
 Latitude.) 
 
 Remarks. — Under the head of Sextant will be found full and 
 practical directions for adjusting the instrument and reading 
 the altitude. (See also Corrected Altitude ; Quadrant ; Oc- 
 tant.) 
 
 If the star telescope is used, be particular to observe as closely 
 as possible in the centre of the field. 
 
 AMPLITUDE.— The bearing (never exceeding 90°) of a 
 heavenly body at rising or setting. To ascertain the variation 
 and deviation of a compass by employing an amplitude, pro- 
 ceed as follows : 
 
 To Find the Magnetic Amplitude. — Observe the sun to 
 rise or set and note its magnetic bearing by the compass, pelorus, 
 or alidade, which bearing will be named east so many degrees 
 north or south at rising, but west so many degrees north or 
 south at setting, as the case may be. 
 
 To Find the True Amplitude.— With the latitude by dead- 
 reckoning to the nearest degree, and the sun's declination to the 
 nearest half degree, enter table 39 and select the sun's true bear- 
 ing, which will be named north if the declination is north, and 
 south if the declination is south. 
 
 To Find the Whole Variation. — The difference between the 
 compass bearing and the true bearing (subtracted if of the same 
 name, but added if of different names) will be the whole amount 
 of the compass variation, or the angle made with the true me- 
 ridian by the compass needle, and it will be named as follows : 
 
 To Name the Variation. — Refer to a compass card and mark 
 the points representing the bearings, then imagine the eye in 
 the centre of the compass looking at the point standing for the 
 magnetic (compass) bearing, and if the true bearing is to the 
 
THE NAVIGATOR'S POCKET-BOOK 9 
 
 right hand of the magnetic bearing the variation is easterly, 
 but if to the left hand it is westerly. 
 
 To Find the Deviation. — If the compass has no deviation, 
 then the whole amount of the variation determined by the am- 
 plitude will agree with the variation given by the chart for the 
 ship's position, but if they do not agree, their difference will be 
 the deviation of the compass for that particular course the ship 
 was heading at the time of the observation, and it will be named 
 according to the following : 
 
 To Name the Deviation. — Suppose that the variation found 
 by amplitude is 10° east, and the variation given by the chart is 
 5° west. Now as the chart tells us that the north point of our 
 compass needle in order to be correct magnetic should be in- 
 clined 5° to the west of the geographical or true north, and we 
 find by our observation that it is inclined 10° to the east, it stands 
 that the compass has 15° of easterly deviation. 
 
 Again, suppose the variation found by amplitude is 8° east, 
 and the variation given by chart is 3° east, it shows that the com- 
 pass needle is deflected 5° too much to the east, hence easterly 
 deviation. 
 
 Once more, suppose that the variation found by amplitude is 
 15° west and the variation given by chart is 13° west ; it shows 
 that the compass needle has 2° of westerly deviation. 
 
 AMPLITUDE TABLES.— True bearings of heavenly bodies 
 at rising and setting, calculated for various latitudes and dec- 
 linations. 
 
 ANEMOMETER. — An instrument that measures the force 
 of the wind. 
 
 ANEROID BAROMETER. — An instrument that registers 
 atmospheric pressure, its principle of construction being as fol- 
 
10 THE NAVIGATOR'S POCKET-BOOK 
 
 lows : The weight of the atmosphere presses on a thin metal 
 box from which the air has been extracted and which is kept 
 from collapsing by a spring. To this box is secured by a me- 
 chanical arrangement the index-hand that moves around the dial 
 or face of the barometer. When the atmospheric pressure in- 
 creases a spring, acting on a lever, turns the hand to the right, 
 and when the pressure decreases the hand turns to the left. (See 
 Barometer.) 
 
 ANGLE.— The divergence of two lines starting from the 
 same point. (See Angle of Incidence.) 
 
 ANGULAR DISTANCE.— Measured by an angle ; a certain 
 number of degrees of arc. 
 
 ANNUAL VARIATION.— The yearly change of the com- 
 pass variation in the same locality, or the yearly change of dec- 
 lination and right ascension tabulated for the fixed stars. 
 
 ANTARCTIC CIRCLE.— The parallel of 66° 32', which di- 
 vides the south temperate from the south frigid zone. 
 
 APPARENT TIME.— Time calculated by the sun. When 
 the sun crosses the meridian of the observer it is apparent noon 
 where he is, as well as at all places on his meridian from pole to 
 pole. 
 
 ARC. — A part of a circle. (See Diurnal Arc ; Nocturnal Arc ; 
 Sextant.) 
 
 ARCTIC CIRCLE,— The parallel of 66° 32', which divides 
 the north temperate from the north frigid zone. 
 
 ARITHMETIC OF NAVIGATION.— The arithmetic of 
 practical navigation is extremely simple and is included in the 
 following: 
 
THE NAVIGATOR'S POCKET-BOOK 11 
 
 Angular Measure. — 
 
 60 seconds (60") make 1 minute (1'). 
 60 minutes (60') make 1 degree (1°). 
 Time Measure. — 
 
 60 seconds (60 sec.) make 1 minute (1 m.). 
 60 minutes (60 m.) make 1 hour (1 h.). 
 To Convert Time into Arc. — Convert hours, minutes, and 
 seconds into arc according to table 7 or by the following : 
 1 hour is equal to 15°, so multiply the hours by 15. 
 4 m. is equal to 1°, so divide the minutes by 4. 
 4 sec. is equal to 1', so divide the seconds by 4. 
 To Convert Arc into Time. — Multiply the longitude by 4 
 and this will turn the degrees of arc into minutes of time, the 
 minutes of arc into seconds of time, and the seconds of arc into 
 what is known as thirds of time (a third is the name given to 
 the sixtieth part of a second). By dividing by 60 these quanti- 
 ties will be reduced to hours, minutes, and seconds of time. 
 (See table 7.) 
 
 Arithmetical Signs. — 
 
 == equal to, the sign of equality. 
 H- plus, the sign of addition. 
 — minus, the sign of subtraction. 
 x multiplied by, the sign of multiplication. 
 -f- divided by, the sign of division. 
 Addition of Degrees, Minutes, and Seconds. — 
 35° 30' 20" 27° 27' 56" 
 
 20° 20' 30 " 36° 57' 49 " 
 
 55° 50' 50" 64° 25' 45" 
 
 Subtraction of Degrees, Minutes, and Seconds. — 
 11° 12' 10" 26° 35' 42" 
 
 10° 10' 10" 12° 45' 50" 
 
 1° 02' 00" 13° 49' 52" 
 
12 THE NAVIGATOR'S POCKET-BOOK 
 
 Multiplication of Degrees, Minutes, and Seconds. — 
 
 10° 10' 10" 13° 59' 58" 
 
 _5 3 
 
 50° 50' 50" 41° 59' 54" 
 
 Division of Degrees, Minutes, and Seconds. — 
 
 2)40° 20' 10" 2)37° 15' 52" 
 
 20° 10' 05" 
 
 18° 37' 56 
 
 Addition of Decimals. — 
 
 
 6.5 
 
 7.9 
 
 5.2 
 
 6.9 
 
 3.2 
 
 4.9 
 
 14.9 
 
 19.7 
 
 Subtraction of Decimals. — 
 
 
 19.7 
 
 29.5 
 
 4.3 
 
 13.6 
 
 15.4 
 
 15.9 
 
 Multiplication of Decimals. — 
 
 
 20.1 
 
 15.6 
 
 5 
 
 4 
 
 100.5 
 
 62.4 
 
 Division of Decimals. — 
 
 
 2)18.4 
 
 2)17.6 
 
 9.2 
 
 8.8 
 
 ARTIFICIAL HORIZON.— A small trough rilled wilh 
 quicksilver, which latter is protected from the ruffling effects 
 of the wind by a glass roof. It is used on shore to catch the 
 image of a heavenly body and to measure its altitude for the 4 
 purpose of determining the latitude and longitude. A pan of 
 
THE NAVIGATOR'S POCKET-BOOK 13 
 
 molasses or liquid tar has often been employed with fairly good 
 results, in the absence of a regular artificial horizon. 
 
 The theory of the artificial horizon is based upon the estab- 
 lished principle that the angle of reflection is equal to the angle 
 of incidence — that a ray of light striking a plane-reflecting sur- 
 face will leave it at the same angle precisely. 
 
 Rules. — Place the trough on firm ground and as free from the 
 wind as possible so that the surface of the liquid may not be 
 disturbed, then face the heavenly body and step backward until 
 its reflection is seen in the quicksilver. The image will now be 
 brought down by the sextant until it is in contact with the other 
 image in the trough, and the angle shown on the sextant will be 
 double the altitude of the body, consequently it will be divided 
 by 2. 
 
 When observing the lower limb of the sun in the morning the 
 images will separate, but in the afternoon they will close. 
 
 In the case of the sun, if the nearest limbs of the two images 
 are brought in contact half of the angle obtained by the sextant 
 will be the altitude of the lower limb, but if the farthest limbs 
 are brought in contact half of the angle obtained will be the 
 altitude of the upper limb, and the semi-diameter will be applied 
 according to the regular rules given for the sun under the head 
 of Corrected Altitude. The sun's altitude obtained must also 
 be corrected for parallax and refraction, but not for dip, because 
 that quantity is eliminated by the use of the artificial horizon. 
 
 When ready to observe the altitude for a time sight it is best 
 to separate the images or overlap them a trifle, as the case may 
 require ; then wait, in the first place, for them to kiss (close), or, 
 in the second place, for the limbs to all but part, and at such 
 instant of perfect contact note the Greenwich time and proceed 
 to find the place of the observer by the given rules. 
 
14 THE NAVIGATOR'S POCKET-BOOK 
 
 Before observing an altitude the glass roof should be carefully 
 wiped clean, and if dust-scum is seen to rest on the surface of 
 the mercury it should be brushed off. 
 
 "When equal altitudes are observed be sure to measure the same 
 limb in the p.m. that was measured in the a.m.; otherwise the 
 result will be unsatisfactory. 
 
 It is to be explained that when a heavenly body is much more 
 than 60° above the horizon it cannot, as a rule, be measured by 
 an artificial horizon, because on the majority of sextants the 
 reading does not go far above 120°. 
 
 ASTRONOMICAL DAY.— This commences at noon of the 
 civil day, the hours being counted numerically from 1 to 24, so 
 that the day begins and ends at noon. 
 
 ASTRONOMICAL TIME.— The civil day begins at mid- 
 night, twelve hours before the astronomical day, which com- 
 mences at noon. To convert civil time into astronomical time 
 it is only necessary to proceed as follows : 
 
 If the civil time is a.m. take one from the date and add 12 to 
 the hours ; but if the civil time is p.m. simply take away the 
 sign p.m., and the answer will be. the astronomical time. 
 
 To change astronomical time into civil time, if the hours are 
 less than twelve, simply write p.m. after them ; but if the hours 
 are more than twelve subtract twelve hours from them, call the 
 remainder a.m., and add 1 to the days of the month. 
 
 ASTRONOMY.— That science which treats of the heavenly 
 bodies, their orbits, distances, etc. 
 
 AUGMENTED ALTITUDE.— Increased altitude ; the cor- 
 rection in arc added to an ex-meridian altitude. 
 
 AUTUMNAL EQUINOX.— The period of the year when 
 the sun crosses the equator from northern into southern declina 
 
THE NAVIGATOK'S POCKET-BOOK 15 
 
 tions. This is known as the First Point of Libra. (See Spring 
 Equinox.) 
 
 AXIS. — A line on which a body is supposed to revolve. 
 
 AXIS OF COLLIMATION.— The line of sight in an instru- 
 ment, being the line which passes through the centre of the 
 object-glass and the intersection of the wires placed in its focus. 
 What is known as the error of collimation is the difference 
 between the actual line of sight and the position which that line 
 should have in reference to the axis of motion of the instrument. 
 Should the line of sight of the telescope be inclined to the plane 
 of the instrument, instead of perfectly parallel to it, all angles 
 measured by the sextant will be too great, 
 
 AZIMUTH.— The bearing (never exceeding 180 c ) of a heav- 
 enly body calculated from the north or south points of the 
 heavens. To ascertain the variation and deviation of the com- 
 pass by an azimuth, proceed as follows : 
 
 To Find the Magnetic Azimuth and Time. — Observe the 
 sun's bearing by compass, alidade, or pelorus, and note the local 
 time shown by the ship's clock, which latter correct by adding 
 to it four minutes of time for every degree of longitude sailed 
 east since the clock was last set, but by subtracting four min- 
 utes for every degree sailed west. 
 
 In north latitudes a.m. azimuth bearings are counted north so 
 many degrees east, and p.m. azimuth bearings are counted north 
 so many degrees west. 
 
 In south latitudes a.m. azimuth bearings are counted south so 
 many degrees east, and p.m. azimuth bearings are counted south 
 so many degrees west. 
 
 To Find the True Azimuth. — With the corrected local ap- 
 parent time and the latitude of the ship to the nearest degree 
 
16 THE NAVIGATOR'S POCKET-BOOK 
 
 by dead-reckoning, also the declination of the sun to the nearest 
 degree, enter the azimuth tables and select the sun's true bearing. 
 
 To Find the Whole Variation. — The difference between the 
 compass and true bearings (always found by subtracting one 
 from the other) will be the whole amount of the variation of 
 the compass needle from the true north, and it will be named as 
 follows : 
 
 To Name the Variation. — Refer to a compass card and mark 
 the two points representing the bearings, then imagine the eye 
 in the centre of the compass looking at the point standing for 
 the magnetic (compass) bearing, and if the true bearing is to the 
 right hand of the magnetic bearing the variation is easterly, but 
 if to the left hand, it is westerly. 
 
 To Find the Deviation. — If the compass has no deviation, 
 then the whole amount of the variation determined by the azi- 
 muth will agree with the variation given by the chart for the 
 ship's position, but if they do not agree their difference will be 
 the deviation of the compass for that particular course headed 
 by the ship at the time of the observation, and it will be named 
 according to the following : 
 
 To Name the Deviation. — Suppose that the variation found 
 by azimuth is 7° west and the variation given by chart is 9° east. 
 ISfow as the chart tells us that the north point of our compass 
 needle in order to point correct magnetic should be inclined 9° 
 to the east of the geographical or true north, and we find by our 
 observation that it is inclined 7° to the west, it stands that the 
 compass has 16° of westerly deviation. 
 
 Again, suppose that the variation found by azimuth is 14° 
 west and the variation given by chart is 6° west : it shows that 
 the compass needle is deflected 8° too much to the w T est, hence 
 westerly deviation. 
 
THE NAVIGATOR'S POCKET-BOOK 17 
 
 Once more, suppose that the variation found by azimuth is 
 20° east and the variation given by the chart is 19° east : it 
 proves that the compass needle has 1° of easterly deviation. 
 
 AZIMUTH ATTACHMENT.— A small, portable, mechani- 
 cal device, consisting of two revolving arms or sight-vanes, for 
 resting on the compass-glass and by which bearings are taken. 
 (See Alidade ; Pelorus.) 
 
 AZIMUTH CIRCLE.— Another name for an azimuth at- 
 tachment. 
 
 AZIMUTH COMPASS.— A portable, dry -card compass 
 provided with sight- vanes and used for taking bearings. It is 
 now obsolete. 
 
 AZIMUTH MIRROR.— A small, portable instrument pro- 
 vided with a silvered glass and used for taking bearings. It 
 steps in a small, shallow hole bored in the centre of the com- 
 pass-glass, and is turned around until the image of the desired 
 object is seen in the mirror, when its bearing is read. (See Ali- 
 dade ; Azimuth Attachment ; Pelorus.) 
 
 AZIMUTH TABLES.— True bearings of the sun calculated 
 for various latitudes, declinations, and times from sunrise to 
 sunset. 
 
 BACK SHADES.— (See Sextant.) 
 
 BAROMETER. — An instrument for measuring the weight 
 or pressure of the atmosphere, and sometimes referred to as a 
 weather-glass, as it indicates the probable changes in the weather. 
 The normal condition or average standing of the barometer for 
 the sea-level is about thirty inches. As a rule, when the barom- 
 eter continues steady, settled weather may be anticipated ; but 
 if it is unsteady, a change is promised. A sudden rise of the 
 2 
 
18 THE NAVIGATOR'S POCKET-BOOK 
 
 barometer is nearly as bad as a sudden fall, as it proves that the 
 equilibrium of the atmosphere is unsettled. The average range 
 (rise and fall) of the barometer in the higher latitudes is 1.5 (one 
 inch and five-tenths) ; in the intertropical parallels from 0.2 to 
 0.4 (two to four-tenths), and near the equator only 0.15 (fifteen- 
 hundred ths of an inch). In hurricanes the barometer ranges 
 from 1.0 to 2.5 (one to two and a half inches) — the rapidity of 
 the fall increasing as the storm-centre approaches. 
 
 On the mercurial barometer the scale is spaced off in inches, 
 whence is derived such terms as " the barometer staudsat thirty 
 inches/' etc., meaniDg in this instance that the level of the mer- 
 cury in the glass tube is opposite the thirty-inch division of the 
 scale. (See Aneroid Barometer ; Mercurial Barometer ; Law of 
 Storms; Weather.) 
 
 BASE-LINE. — The lowest side of a geometrical figure ; at 
 a right angle to the perpendicular. 
 
 BEARING. — The direction of one object from another ac- 
 cording to the compass. (See Alidade ; Azimuth Attachment ; 
 Pelorus.) 
 
 BELOW THE POLE. — When the north star is situated so 
 that the pole is intercepted between it and the observer, it is said 
 to be below the pole. This applies to other circumpolar bodies. 
 (See Latitude ; Upper Transit.) 
 
 BOXING THE COMPASS.— (See Compass.) 
 
 CARDINAL POINTS.— North, East, South, and West. (See 
 Intercardinal Points.) 
 
 CELESTIAL.— Relating to the heavens. 
 
 CELESTIAL CONCAVE.— The heavens. 
 
 CHART.— A marine map showing coasts, shoals, etc., etc. 
 
THE NAVIGATOR'S POCKET-BOOK 19 
 
 All charts are projected true (parallels and meridians geographi- 
 cal), but the compass diagrams printed on them may be either 
 true or magnetic, as described under the head of Chart Sailing. 
 The parallels are represented by straight lines drawn true east 
 and west across the chart, and the meridians by straight lines 
 drawn true north and south. If the degrees and minutes marked 
 on the right and left hand margins of the chart increase upward, 
 the chart represents north latitudes, but if they decrease upward 
 the chart represents south latitudes. If the degrees and minutes 
 marked on the top and bottom margins of the chart increase 
 toward the right hand, the chart represents east longitudes, but 
 if they decrease toward the right hand the chart represents west 
 longitudes. Charts are drawn on a large scale or a small scale 
 according to the extent of ocean or coast to be delineated, and it 
 is to be understood that buoyage, lights, soundings, etc., are 
 fully explained on the charts representing the waters they refer 
 to, and such explanations and directions as are given apply 
 especially to that particular chart on which the details are read. 
 
 Buoys are marked B. (black), Cheq. (chequered), H. S. (hori- 
 zontal stripes), R (reel), W. (white), B. W. (black and white), 
 B. R. (black and red), R. W. (red and white), V. S. (vertical 
 stripes). Buoys painted with black and white perpendicular 
 stripes mark a mid-channel and must be passed close to to avoid 
 danger. A green buoy marks a wreck. Perches with balls, 
 cages, etc., mark turning-points in the channel. On the coast 
 of the United States, when approaching a channel from seaward, 
 red buoys with even numbers are left on the starboard side, and 
 black buoys with odd numbers are left on the port side. Buoys 
 painted with red and black horizontal stripes indicate obstruc- 
 tions with channel -ways on either side. 
 
 The quality of the bottom is expressed in abbreviations, as 
 
20 THE KAVIGATOK'S POCKET-BOOK 
 
 follows : blk. (black), b. (blue), bkn. (broken), br. (brown), cl. 
 (clay), co. (coarse), crl. (coral), d. (dark), f. (fine), gy. (gray), g. 
 (gravel), gn. (green), grd. (ground), h. (hard), m. (mud), oz. 
 (ooze), oys. (oysters), peb. (pebbles), rd. (red), r. (rock), rot. 
 (rotten), s. (sand), sli. (shells), sft. (soft), spk. (speckled), stf. 
 (stiff), st. (stones), wd. (weed), w. (white), y. (yellow). 
 
 Soundings, unless otherwise specified, are indicated according 
 to the following : The numerals marked on the white surfaces 
 represent the depth of the water at that point in fathoms (six 
 feet), and when marked on the dotted surfaces they indicate the 
 depth in feet (12 inches). All soundings are given for mean 
 low water, and the rise of the tide at the given place is to be 
 added to the sounding to ascertain the greatest depth of water 
 at high tide at that particular point. 
 
 During fog or falling snow, vessels approaching light-ships 
 will be warned by the alternate ringing of a bell and the blow- 
 ing of a fog-horn. 
 
 Lights are shown by a dot of yellow having a red spot in the 
 middle, and if any uncertainty exists concerning the character 
 of a light it is simply marked Lt. Other abbreviations and 
 their significance are as follows : F. (fixed), Fl. (flashing), Int. 
 (intermittent), Eev. (revolving), F. and Fl. (fixed and flashing 
 alternately), Fig. (floating), Lt. Yes. (light-vessel). When no 
 color is expressed the light may be taken to be white. When- 
 ever the color is given the word is spelled in full, as red, etc. 
 
 Currents are shown by a feathered arrow; the direction of the 
 same indicating the flow of the current. Flood- tide stream is 
 indicated by an arrow feathered on one side only, and ebb-tide 
 stream by an unfeathered arrow. 
 
 Rocks just below the surface of the water are shown by a 
 small dotted circle having a cross in the centre. Rocks awash 
 
THE NAVIGATOR'S POCKET-BOOK 21 
 
 or just above water are shown by a dotted circle with one or 
 more dots inclosed according to the number or extent of the 
 rocks indicated. A dotted circle with a numeral in it signifies 
 a shoal with the number of feet or fathoms over it. Either a 
 rock, an island, or a shoal marked E. D. signifies existence 
 doubtful, and if marked P. D., it means position doubtful, al- 
 though known to exist. (See Pricking Position.) 
 
 Mercator's Chart. — This is the chart universally adopted as 
 the only proper chart for general navigation. The parallels 
 and meridians are all straight parallel lines, but the meridians 
 only are equidistant. The distance between the parallels in- 
 creases from the equator toward the poles in proportion as the 
 meridians converge. This chart projection is constructed by 
 the aid of the table of meridional parts and the rule given in 
 Bow ditch. 
 
 On the surface of the globe the parallels of latitude are every- 
 where equidistant, while the distance between the meridians 
 lessens as we proceed polar wise. Thus it will be appreciated 
 that if on a plane chart the parallels are retained equidistant 
 while the meridians are widened out in order to show them as 
 straight lines and as far apart in the vicinity of the poles as 
 they are at the equator, there must be considerable distortion in 
 one direction — namely, the longitude. This difficulty of de- 
 lineation may be surmounted and the relation between the 
 principal parts maintained by also distorting the chart polarwise 
 or in a north and south direction; consequently the distance be- 
 tween the parallels is widened in the same proportion that the 
 meridians have been widened. Of course this will distort the 
 land and sea more and more in the parallels approaching 
 the poles, but as the scale on the right and left hand margins of 
 the chart allows for this, and as the contour of the countries is 
 
22 THE navigator's pocket-book 
 
 preserved, as well as the relative directions from one point to 
 another, no inconvenience is experienced by the navigator. 
 (See Chart Sailing.) 
 
 Chart of the Inclination. — A chart which shows the dip of 
 the magnetic needle for various latitudes and longitudes. 
 
 Coast Survey Chart. — A chart of the coast published by 
 Government. 
 
 General Chart. — A chart embracing a large expanse of ocean 
 or extent of coast. 
 
 Harbor Chart. — A chart, as its name implies, which de- 
 lineates a harbor. 
 
 It is a detached portion of a general chart and is shown on a 
 large scale. As a rule the parallels and meridians are not 
 shown on harbor charts, and the scale is given in miles. 
 
 Physical Chart. — A chart showing ocean currents, winds, 
 ice limits, etc. 
 
 Great Circle Chart. — A chart constructed specially so that 
 all great circles are represented as straight lines. This answers 
 the same purpose for great-circle sailing that Mercator's chart 
 answers for rhumb-sailing. The construction of the great-circle 
 chart is such that a straight line drawn on it connecting the 
 place of departure with the place of destination gives imme- 
 diately the great-circle track. 
 
 Hydrographic Charts. — Charts published by the Washington 
 Hydrographic Office, which delineate the navigable waters of 
 the world, rocks, shoals, tides, currents, depths, etc., and give 
 the varied information in a convenient form for the navigator. 
 The surveys are made by American naval officers and the charts 
 are published by the United States Government. 
 
 Variation Chart. — A chart of the world on Mercator's pro- 
 jection, on which is represented the variation of the compass in 
 
THE NAVIGATOR'S POCKET-BOOK 23 
 
 different latitudes and longitudes by a series of curved lines ; 
 also known as an isogonic chart. 
 
 CHART SAILING. — This ebmraces several considerations, 
 which will be taken up in order. 
 
 To Shape the Course.— Place the same bevelled edge of the 
 parallel rules over the ship's place and the point bound to ; then, 
 preserving the angle, slide the edge to the nearest compass dia- 
 gram printed on the chart until it lies on the dot in the centre ; 
 now read the compass-point looking toward the place sought, 
 and that will be the required course. (See Course Protractor ; 
 Graduated Rulers.) 
 
 In case the distance between the two places is too great to be 
 reached by the parallel rules, take a piece of string and stretch 
 it from one point to the other by the aid of pins stuck in the 
 chart through the two places ; then lay the bevelled edge of the 
 rule against the string to obtain the angle, and proceed as before 
 explained. 
 
 To Allow for Variation. — On some charts the north and 
 south line of the diagram compass is parallel with the meridian 
 line, while on other charts the north and south line of the dia- 
 gram compass forms an angle with the meridian line. In the 
 latter case it proves that the diagram indicates magnetic direc- 
 tions ; consequently the course found by the parallel rules will 
 be steered (unless deviation exists), as the diagram on the chart 
 is a reflection of the compass on board the vessel. On the other 
 hand, where the north and south line of the diagram compass 
 is parallel with the meridian, it proves that the diagram indi- 
 cates true or geographical directions. In this case it becomes 
 necessary to allow for the variation of the compass as fol- 
 lows : 
 
 Example. — Suppose that the course found by a true compass 
 
24 THE navigator's pocket-book 
 
 diagram is north and the chart tells us that where the ship is 
 situated there is one point of westerly variation, which means 
 that the north end of the compass needle is inclined one point 
 to the west of the true or geographical noith. Under these 
 circumstances, it will be necessary to steer north-by-east by the 
 ship's compass in order to make a true north course. 
 
 Note. — A simple rule to remember for converting true courses 
 into magnetic courses is to allow the amount of westerly varia- 
 tion away from the true course in the direction that the Jiands 
 of a watch revolve, and easterly variation contrary, or against 
 the hands of a watch. 
 
 To Allow for Deviation. — If deviation exists for the correct 
 magnetic course found, then the correct magnetic course must 
 have the amount of the deviation applied to it on exactly the 
 same principle as explained for variation in the preceding para- 
 graph. 
 
 Example. — The correct magnetic course is east and there is 
 one point of westerly deviation to be allowed when the ship's 
 head is on that course ; consequently the compass course to be 
 steered is east-by-south in order to make a correct magnetic east 
 course. 
 
 Always apply the variation before applying the deviation. 
 
 To Measure the Distance. — Contain between the points of 
 the dividers the position of the ship and the port bound to, then 
 apply this span to the graduated meridian (side margin or bor- 
 der) of the chart directly opposite the latitudes you are to sail in, 
 and read the distance indicated. 
 
 If the span is too great to be contained between the points of 
 the dividers, then set the latter to any convenient number of 
 miles or degrees by the scale on the side of the chart opposite the 
 latitudes the ship is to traverse, and ascertain the number of 
 
THE ^AYIGATOK'S POCKET-BOOK 25 
 
 times that this " set" is contained on the direct line of the ship's 
 course, and so calculate the distance. 
 
 The reason for setting the dividers to the scale opposite the 
 parallels to be sailed in is on account of that particular scale 
 belonging to those parallels. As explained under the head of 
 Charts, the distance between the parallels increases from the 
 equator toward the poles, consequently the scale given for the 
 parallels near the equator will not answer for higher latitudes. 
 
 The two graduated parallels (top and bottom margins on bor- 
 ders) on the chart are marked in degrees and minutes, but on 
 these parallels longitude-in-arc is measured, nothing more ; dis- 
 tance cannot be taken from them, and they are only employed 
 for laying off the longitude. 
 
 Cross-Bearings. — Observe in quick succession the compass- 
 bearings of two lights (or other stationary objects which are 
 defined on the chart), then refer to the chart, and by the aid of 
 the parallel rules and the magnetic diagram compass draw pencil 
 lines along the paper from the lights in question, according to 
 the respective bearings of the two objects, and the point where 
 the lines cross will show the position of the ship at the time the 
 bearings were taken. 
 
 Remarks. — It is to be understood that the compass bearings 
 are to be corrected for the deviation (if any exists) of the ship's 
 head at the time the bearings were taken, so as to convert them 
 into correct magnetic bearings before applying the lines to the 
 chart. 
 
 It must be remembered that if the chart is provided with true, 
 instead of magnetic compass diagrams, the variation of the com- 
 pass must also be applied to the respective bearings in order to 
 convert them into true bearings ; then these latter must be trans- 
 ferred to the chart, plotting them from the true compass diagram. 
 
26 THE navigator's pocket-book 
 
 Vertical Danger Angle. — The danger angle Las, to a great 
 extent, taken the place of cross-bearings for locating the posi- 
 tion of a vessel when in sight of lighthouses, either by day or 
 night. It is extremely easy of solution, and by the aid of the 
 danger-angle tables to be found in the back of this little volume 
 the navigator will discover it to be a very simple matter, both to 
 fix the position of his ship and to keep outside of dangers in the 
 way of rocks and shoals situated at a distance from the shore. 
 (See Danger-xAngle Tables.) 
 
 First Consideration. — To determine the place of the ship, 
 take a compass-bearing of any lighthouse in sight ; the vessel 
 will be somewhere on this line of bearing. Then with the 
 sextant measure the altitude of the light by throwing the reflec- 
 tion of the lantern to the water line. By consulting the danger- 
 angle tables with the measured angle and the height of the light 
 above the sea-level (the latter is given on the chart) the distance 
 of the vessel seawards from the light will be read in the side 
 column to the left. 
 
 Second Consideration. — To explain another practical applica- 
 tion of the vertical danger angle, let it be supposed that a ves- 
 sel is forced to closely round a lighthouse, at some distance 
 seawards of which there is a cluster of rocks a few feet under 
 water. Now with the dividers measure the distance from the 
 light to a point well outside of the danger, then with this dis- 
 tance and the height of the light enter the danger-angle tables 
 and read the angle given. Place this angle on the sextant and 
 when approaching and passing the light observe that this angle 
 does not increase, otherwise the ship will be inside the danger 
 mark. If the angle decreases the ship will be farther outside 
 the danger mark than there is necessity 7 for. 
 
 Remarks. — In measuring vertical danger angles, when the 
 
THE NAVIGATOR'S POCKET-BOOK 27 
 
 lighthouse is comparatively close, the observer should get as 
 near to the surface of the water as the deck will admit in order 
 to reduce the error arising from the eye being elevated above 
 the sea -level. It is to be explained, however, that if this 
 point is disregarded altogether, the slight error will lie on the 
 safe side, so long as there exists no danger seawards of the 
 ship. 
 
 If the sextant has an index-error the same must be allowed 
 for in measuring danger angles. (See Sextant.) 
 
 Horizontal Danger Angle. — Where the vertical danger angle 
 is dependent upon a lighthouse, the height of which is known, 
 the horizontal danger angle may not only be worked by two 
 lighthouses independent of their height, bnt in the daytime it 
 may be employed by using any two well-defined objects on 
 shore, such, for instance, as prominent features of the coast-line, 
 buildings, etc. In the horizontal danger angle no tables are 
 used, the navigator calculating his own angle. 
 
 We will suppose that the chart shows a number of rocks or 
 shoals stretching for some little distance along the coast, and 
 that back of them on the shore are a life-saving station and a 
 church. Sweep the smallest circle with a pencil point dividers 
 that will pass through the two shore objects and inclose all the 
 dangerous features between them. Now from a seawards point 
 on this circle, draw lines to the two objects on shore so that the 
 lines will look like the plotting of a cross-bearing. The respect- 
 ive directions of these two lines will be measured by the parallel 
 rules and the nearest chart compass, and the angle shown by the 
 divergence of the lines will be turned into degrees. This angle 
 will be placed on the sextant, and when approaching and pass- 
 ing the danger the navigator will observe that the angle does 
 not increase, otherwise he will know that he is inside the danger 
 
28 the navigator's pocket-book 
 
 line. If the angle decreases it is a sign that he is outside or sea- 
 wards of the danger line. 
 
 As its name implies, this angle is measured by holding the 
 sextant horizontal and sweeping one object into the other. 
 
 It matters not from what seawards point of the circumference 
 of this circle the angle is measured — it will give the same re- 
 sult ; consequently by steering the ship so as to preserve the 
 given angle, the navigator would sail right around the circle 
 drawn by the pencil-point dividers. 
 
 Example. — We will suppose that off a section of the coast 
 defined by two headlands, several clusters of rock are shown to 
 extend between them and to lie off shore at a distance of two 
 miles. Our course being close along the coast it is necessary to 
 take precautions in approaching and passing this dangerous 
 point. 
 
 By the aid of a pencil-point dividers (or a small piece of lead- 
 pencil fastened to one leg of the common dividers) we sweep a 
 circle which passes through the headlands and incloses every 
 part of the shoal. Next we draw two pencil lines from a sea- 
 wards point on this circle so that they will pass through each 
 headland ; then we ^determine their respective bearings by the 
 parallel rules and the chart compass. 
 
 One headland, we will say, we find to bear north -northeast, 
 and the other northwest. These bearings equal six compass- 
 points, or 67°; consequently this is the horizontal danger angle, 
 and we place the same on the sextant and observe that it does 
 not increase as we approach and pass the shoal. 
 
 Four-Point Bearing. — This is an extremely simple and use- 
 ful problem. When approaching a lighthouse, light-vessel, or 
 a point of land, note its compass-bearing when it is four points 
 on the bow. When the object is exactly abeam calculate the 
 
THE NAVIGATOR'S POCKET-BOOK 29 
 
 distance run from the time the first bearing was taken, and this 
 will be the distance of the ship from the light abeam. 
 
 Example. — A ship is steering north, making ten knots per 
 hour. At 7 o'clock a lighthouse bears northwest, and at 7.30 
 o'clock it bears west, or directly abeam. The distance run in 
 the interval is five miles ; consequently the ship is five miles east 
 of the light. 
 
 Remarks. — The ship is not supposed to change her course in 
 the interval between bearings. 
 
 In this problem the deviation of the compass is not considered, 
 as the vessel maintains the same course ; consequently, the devia- 
 tion being the same for both bearings, it is ignored. 
 
 An object to bear directly abeam must subtend an angle of 
 eight points of the compass, or 90°, to the ship's course ; for ex- 
 ample, if a ship is steering northwest, an object will be directly 
 abeam on the port side when it bears southwest, and directly 
 abeam on the starboard side when it bears northeast. 
 
 Patterson's Method. — This conception of the author's affords 
 the means of locating the vessel by two compass-bearings of the 
 same object when in sight of land, where only a single light, 
 headland, or other fixed feature is to be seen. 
 
 Rule. — Observe the bearing of the object and note the time. 
 After holding the course until the object has changed its bearing 
 at least two or three points, note again its bearing and the time, 
 and calculate the distance the vessel has run in the interval be- 
 tween the first and last bearings. Trace the two lines of bear- 
 ing on the chart in pencil, then span the dividers to the distance 
 run, and proceed as follows : 
 
 With the parallel rules set to the course sailed by the ship be- 
 tween bearings, move them along the pencil lines until both 
 points of the dividers, held against the bevelled edge of the rules, 
 
30 THE NAVIGATOR'S POCKET-BOOK 
 
 just fit across the lines, and these two points where the dividers 
 rest w T ill show the position of the vessel at the time of the first 
 hearing as well as her place at the time of the second bearing. 
 
 Remarks. — The two compass-bearings must be corrected for 
 the deviation (if any exists) of the ship's head at the time the 
 bearings were taken, so as to convert them into correct magnetic 
 bearings before tracing them on the chart. 
 
 The compass course must also have the deviation applied to 
 it so as to reduce it to a correct magnetic course before setting 
 the parallel rules by the diagram compass on the chart. 
 
 CHIP LOG —This log can claim at least one advantage over 
 the patent log, inasmuch as the vessel's rate of speed can be de- 
 termined by it at any given instant, whereas the patent log is 
 useful only for recording a considerable distance run. 
 
 The log line should be about one hundred and fifty fathoms 
 long and marked off in knots, the distance between which should 
 stand for the same part of a sea mile as the 30 seconds sand- 
 glass stands for an hour — namely, the 120th part — which would 
 make the lengths between the knots about fifty-one feet. When 
 a 28 seconds glass is used the length between the knots should 
 be about forty-seven feet. 
 
 It has been found, however, from practical experience, that 
 the chip log records somewhat less than it should owing to the 
 log coming home after being hove. To compensate for this, 
 navigators should shorten the distance between the knots so that 
 for a 30 seconds glass they should be forty-eight feet apart, and 
 for a 28 seconds glass, forty-five feet apart. 
 
 Heaving the Log.— One man holds the reel and another the 
 sand-glass. The officer throws the log chip over the ship's stern, 
 and when he observes that the stray line is run off (about ten fath- 
 oms—this distance being allowed to carry the log out of the in- 
 
THE NAVIGATOR'S POCKET-BOOK 31 
 
 fluence of the ship's wake), he calls " turn ; " the seaman upsets 
 the glass and watches until the sand is run out, then calls " stop." 
 The officer stops the line by a sudden jerk which pulls the plug 
 out of its hole in the chip and so allows the log to float horizon- 
 tal, then observes the number of marks that have passed over the 
 tafirail. The last mark shown indicates the knots, and the dis- 
 tance of the mark outside of the tanrail shows the fractions of 
 the knot estimated in eighths (eight furlongs to the mile). The 
 knots and furlongs give the speed of the vessel in nautical miles 
 or knots. 
 
 Remarks. — When running before a heavy sea, allowance 
 must be made, for the ship will make greater speed than indi- 
 cated by the log. Under such conditions it is customary to add 
 one mile for every ten knots run out. 
 
 Driving against a heavy sea it is the rule to subtract one mile 
 for every ten knots run out. 
 
 In heaving the log, the line must be helped from the reel by 
 the officer, so that no strain is brought upon the chip as it rests 
 in a perpendicular position in the water ; otherwise the wooden 
 peg which forms a part of the bridle will pull out and the log 
 will lie flat on the surface. 
 
 The line must be measured occasionally, and if it is found to 
 be stretched, it must be carefully remarked, otherwise it will 
 prove deceptive. 
 
 Compare the sand-glass at times with a watch to see that it runs 
 out in the prescribed number of seconds. 
 
 The glass is more or less influenced by the weather, running 
 slower in a damp atmosphere than in a dry one. 
 
 In case of accident to the sand-glass, time the log-line by a 
 watch. 
 
 When a vessel is going at a high rate of speed it is usual to use 
 
32 THE NAVIGATORS pocket-book 
 
 a 14 seconds glass and then double the indicated number of knots ; 
 this saves the paying out of a long length of line and the at- 
 tendant effort of hauling it in. 
 
 The first knot on the log line is measured from the white rag, 
 which terminates the ten fathoms allowed to drift the chip far 
 enough astern to be out of the eddies of the wake. When this 
 white rag passes over the taffrail the sand-glass is turned. 
 
 CHRONOMETER. — A marine time-piece constructed with 
 the idea of great accuracy, and set to the time of some first me- 
 ridian. The Americans and English use the time of the me- 
 ridian of Greenwich ; the French that of Paris, etc. 
 
 Care of Chronometers. — Chronometers should be wound at 
 the same hour each day, the key being turned gently so that no 
 shock may be imparted when the key butts. They should be 
 stowed as near the centre of motion as possible, and the tempera- 
 ture near them kept as uniform as possible. When transported 
 by hand they should be clamped securely by the clamp-screw, 
 to prevent them from swinging about in their gimbals. In wind- 
 ing a chronometer the instrument is to be inverted with the left 
 hand and the key turned with the right. At all times, except 
 when being transported by hand, the chronometer must be left 
 to swing freely in its gimbals, like a compass. Never stow a 
 chronometer close against an iron bulkhead, or near an iron 
 stanchion, or, beyond all, near spare compasses or artificial 
 magnets, otherwise magnetism will be induced into the steel 
 balance and ruin the going of the chronometer. Avoid placing 
 a chronometer in the after-end of a screw steamer on account of 
 the vibration . When a chronometer is being transported by hand 
 be careful not to knock it against anything or to give it a sud- 
 den twist. (See Rate.) 
 
THE NAVIGATOR'S POCKET-BOOK 33 
 
 CHRONOMETER COMPARISON. — To determine the 
 error of a chronometer by observatory clocks or by comparing 
 the longitude of the ship found by observation with the known 
 longitude of a visible point of land. 
 
 CHRONOMETER RATE.— (See Rate.) 
 
 CHRONOMETER-TIME SIGHT.— (See Longitude.) 
 
 CIRCUM-MERIDIAN ALTITUDE. — An altitude of a 
 heavenly body observed a short time before or after its meridian 
 passage. This is also known as an ex-meridian altitude. (See 
 Latitude.) 
 
 CIRCUMNAVIGATE.— To sail completely around. To 
 sail around the world is to circumnavigate it. 
 
 CIRCUMNAVIGATOR'S DAY. — In circumnavigating 
 the globe by sailing west the ship and the sun move in the same 
 direction, but by sailing east the ship and the sun move in oppo- 
 site directions. In the former case the sun overtakes the ship, 
 and in the latter case the sun advances to meet the ship. There- 
 fore in sailing west the ship's day is lengthened and in sailing 
 east it is shortened at the rate of one hour for every 15° of 
 longitude made. 
 
 Should a vessel start from Greenwich and sail east until the 
 meridian of 180° was reached, arriving at that point at 2 o'clock 
 in the morning of Sunday, the 20th day of the month (according 
 to the ship's date and time), it would only be 2 o'clock in 
 the afternoon at Greenwich on Saturday, the 19th. Thus the 
 ship's time w r ould be twelve hours ahead of the time at Green- 
 wich. Now if the ship, without changing her date, continued 
 sailing to the eastward until Greenwich was reached, another 
 twelve hours w r ould be gained, and the ship's time would be 
 twenty-four hours, or one day, ahead of the Greenwich time. 
 3 
 
34 THE NAVIGATOR'S POCKET-BOOK 
 
 On the other band, should a vessel start from Greenwich and 
 sail west until the meridian of 180° was reached, arriving at that 
 point at 2 o'clock in the morning of Sunday, the 20th day of 
 the month (according to the ship's date and time), it would be 
 2 o'clock in the afternoon of the same day (Sunday, 20th) at 
 Greenwich, so that the ship's time would be twelve hours behind 
 the Greenwich time. If the ship, without changing her date, 
 continued to sail to the westward until Greenwich was reached, 
 another twelve hours would be lost, and the ship's time would 
 be twenty-four hours, or one day, behind the Greenwich time. 
 
 Rule. — When crossing the meridian of 180°, if the ship is 
 sailing eastward, the navigator must reckon the given day over 
 again, so that there will be two Sundays, or Mondays, or Tues- 
 days, etc., in the log-book for that particular week, according to 
 the day that he crosses. By doing this the ship's date will be 
 found to correspond with the Greenwich date when the vessel 
 reaches that port. 
 
 But w T hen crossing the meridian of 180°, if the ship is sailing 
 westward, the navigator must skip a day, so that there will be a 
 Sunday, or a Monday, or a Tuesday, etc., omitted in the log- 
 book for that particular week, according to the day that he 
 crosses. This insures the ship's date agreeing with the Green- 
 wich date when the vessel reaches the latter port. 
 
 Warning. — The great point for the navigator to bear in mind 
 is that he is not to interfere with the Greenwich date shown by 
 the chronometer, but that he is religiousty to keep the run of 
 and hold on to same, and select the sun's declination, equation, 
 etc., from the nautical almanac for the Greenicich date, and cor- 
 rect the hourly difference of declination, etc., according to the 
 regular rule given under the head of Declination. 
 
 Examples. — A ship leaves Greenwich and sails east, reaching 
 
THE NAVIGATOR'S POCKET-BOOK 35 
 
 the meridian of 180° on Sunday, the 20th (according to the 
 ship's date). Instead of calling the next day Monday, the 21st, 
 it must be considered again as Sunday, the 20th, so that two Sun- 
 days and two 20th days for that month will appear in succession 
 in the log-book. 
 
 A ship leaves Greenwich and sails icesi, reaching the meridian 
 of 180° on Sunday, the 20th (according to the ship's date). In- 
 stead of calling the next day Monday, the 21st, it must be con- 
 sidered as Tuesday, the 22d, so that there will not appear either 
 a Monday or a 21st day for that month in the log book. 
 
 CIVIL TIME. — The civil day consists of twenty-four hours ; 
 it commences at midnight, and the first twelve hours are called 
 a.m., and the latter twelve hours are called p.m. (See a.m. p.m.) 
 
 CLAMP-SCREW.— (See Sextant.) 
 
 CLOUDS.— (See Weather.) 
 
 COLLIMATION.— The line of sight in the direction of any 
 object. (See Axis of Collimation.) 
 
 COMBINED ALTITUDE PROBLEM.— (See Sumner's 
 Method.) 
 
 COMPASS. — The mariner's compass consists of a magnetized 
 steel bar secured parallel to the north and south line of a circu- 
 lar card, which latter is balanced on a pi^ot so as to turn freely 
 in the horizontal plane and to indicate the magnetic meridian. 
 The surface of the card is divided into thirty-two courses with 
 their intermediate quarters, and in addition to this all steam- 
 ships have the circumference of the compass card graduated into 
 degrees. 
 
 Boxing the Compass. — What is known as boxing the com- 
 pass is calling the thirty-two courses in order from north by the 
 
3G THE NAVIGATORS POCKET-BOOK 
 
 way of east, as shown on the diagram in front of this book. 
 To box the compass backward is to call the courses from north 
 by the way of west, or contrary to the order in which the hands 
 of a watch revolve. 
 
 Points and Degrees. — By consulting the diagram it will be 
 seen that compass courses are given a value both in points and 
 degrees, the same commencing at the two poles of the circle 
 (north and south) and ending at the equator line of the compass 
 (east and west). Thus the north and south points are zero and 
 the east and west points have a numerical value of 8 and an 
 angular value of 90°. 
 
 Variation of the Compass. — The compass needle when un- 
 influenced by deviation points to the magnetic poles of the earth, 
 and as these do not coincide with the true or geographical poles, 
 the magnetic meridians form an angle with the true meridians, 
 and this is called the variation of the compass, which varies in 
 extent in different parts of the world. The magnetic north pole 
 is situated on the parallel of 70° north and the meridian of 97° 
 west. The magnetic south pole is situated on the parallel of 70° 
 south and the meridian of 145° east. 
 
 Over the North Atlantic, the greater part of the South At- 
 lantic, and the Indian Ocean, the variation is westerly, and over 
 a part of the South Atlantic and in the -Pacific the variation is 
 easterly. There are places on the surface of the globe where 
 variation does not exist, or in other words, where the compass 
 points true north, and these places are said to be situated on the 
 line of no variation. One of these lines runs through Eastern 
 Europe, Asia, and Australia ; the other through North Ameri- 
 ca, the eastern part of South America, and the southwestern 
 part of the South Atlantic Ocean. 
 
 The magnetic equator is not the same as the earth's equator, 
 
THE NAVIGATOR'S POCKET-BOOK 37 
 
 but an irregular line running round the globe, near the earth's 
 equator, which it crosses in two places, one near the west coast 
 of Africa, the other about the middle of the Pacific Ocean. 
 
 The variation of the compass is not constant, but undergoes 
 an annual change, and the amount of this yearly increase or de- 
 crease will be found plainly marked on charts. 
 
 Deviation of the Compass. — What is known as the devia- 
 tion of the compass is the deflection of the needle from the 
 magnetic meridian, caused in iron sailing ships by the attraction 
 of the hull and iron lowermasts, and in an iron steamship by 
 the attraction of the hull, machinery, smokestack and masts. 
 In addition to this it must be understood that deviation is often 
 caused by certain elements of magnetism in the cargo. The 
 manner of ascertaining the existence and extent of compass de- 
 viation will be found explained under the heads of Amplitude 
 and Azimuth. When shaping a course, or when taking com- 
 pass-bearings, the deviation existing for the ship's head must be 
 considered, as explained under the head of Chart Sailing. De- 
 viation is named east or west according as the north point of 
 the compass is drawn to the eastward or westward of the mag- 
 netic meridian. 
 
 Deviation Card. — This is a tabulated account of the devia- 
 tion of the compass for each one of the thirty-two courses, and 
 directs the navigator as to the course to be steered by compass 
 in order to make the required correct magnetic course. Devia- 
 tion always refers to the ship's head. In other words, where 
 deviation is given it means for a certain course. If the card 
 tells us that for an east course the compass has 10° of westerly 
 deviation, it signifies that when the ship heads east the north end 
 of the compass needle will be drawn 10° to the westward of the 
 correct magnetic north, and any bearing taken when the ship is 
 
38 the navigator's pocket-book 
 
 on such course must be corrected for 10° of westerly deviation, 
 and not for the deviation given for the point represented by the 
 bearing. 
 
 A deviation card refers to one particular compass, and to no 
 other, consequently a course set or a bearing taken by a certain 
 compass must have the deviation of that compass applied to it 
 according to its own deviation card. 
 
 Residual Errors. — When a compass is affected by deviation 
 it is sought to adjust it by placing artificial magnets in its 
 vicinity, so as to draw the compass needle to the correct mag- 
 netic meridian, and the remaining deviations for the various 
 courses are classed as residual errors. 
 
 Loeal Attraction of the Compass. — Elements of magnetism 
 outside (away) from the vessel which influence the pointing of 
 the compass. In sailing very close along some coasts where 
 there are large deposits of iron ore or volcanic disturbances the 
 compass has been found to be slightly and temporarily drawn 
 away from the correct magnetic north. It will be understood 
 that, as its name implies, this disturbing quantity is purely 
 local. A vessel's compass is often affected when lying alongside 
 of a dock or other vessel, owing to the near presence of iron 
 used in construction of same. (See Compensated, Demagnet- 
 ized, Dry, Elevated, Liquid, Masthead, Oil, Pole, Spirit, Stand- 
 ard, Steering, and Tripod Compasses.) 
 
 COMPASS ADJUSTING.— Correcting a compass for devia- 
 tion by placing artificial magnets in its immediate vicinity, so as 
 to draw the north end of the compass needle to the correct mag- 
 netic north. As a rule compass adjusting-is performed by pro- 
 fessional adjusters, it being a profession in itself, "although there 
 are shipmasters who have made a study of the science, and in 
 consequence are able to dispense with outside talent. In the 
 
THE NAVIGATOR'S POCKET-BOOK 39 
 
 case of tlie patent-adjusting-binnacle compass, where the mag- 
 nets are contained in racks within the binnacle stand, full direc- 
 tions for adjusting the compass are furnished with the instru- 
 ment. 
 
 COMPASS-BEARING.— The direction of an object accord- 
 ing to one of the divisions of the compass card. 
 
 COMPASS CARD. — The circle to which is secured the mag- 
 netized bar of steel and on which circle the thirty-two compass 
 courses are shown. 
 
 COMPASS CORRECTIONS. — Allowances for variation 
 and deviation. 
 
 COMPASS COURSE.— The track made by a vessel accord- 
 ing to one of the divisions of the compass card. 
 
 COMPASS NEEDLE.— The name often applied to the 
 magnetized steel bar secured to the compass card. 
 
 COMPASS POINT.— One of the divisions of the compass 
 card. 
 
 COMPASS ROSE. — The diagram compass on a chart is 
 referred to in some works on navigation as a compass rose. 
 
 COMPENSATED COMPASS.— An adjusted compass; a 
 compass that has been freed, to a greater or less extent, of its 
 deviation by the employment of artificial magnets, the same 
 being placed in close proximity to the compass, so as to draw 
 the needle to the correct magnetic meridian. 
 
 COMPENSATING MAGNETS.— Artificial magnets used 
 in compass adjusting. (See Magnet.) 
 
 COMPLEMENT.— The full number or quantity; what an 
 altitude lacks of 90° . The zenith distance is the complement 
 of the altitude. 
 
40 THE NAVIGATOR'S POCKET-BOOK 
 
 CO-LATITUDE.— The complement of the latitude, or what 
 it lacks of 90°; as, for instance, 50° is the co-latitude of 40°. 
 
 COMPOSITE SAILING.— This is a combination of great- 
 circle and parallel sailing, and is adopted when the great-circle 
 track, by passing in the neighborhood of ice, land, or other dan- 
 ger, becomes impracticable. In other words, it is a modification 
 of the great-circle track. (See Great- Circle Sailing.) 
 
 CONSTELLATION.— A group of stars to which is given 
 the name of some classical hero, beast, bird, fish, figure, etc. 
 The Pole Star is in the constellation of Ursa Minor (The Little 
 Bear), and the Dipper is in the constellation of Ursa Major (The 
 Great Bear), etc. (See Fixed Stars ; Planets.) 
 
 CORRECTED ALTITUDE.— The observed altitude of a 
 heavenly body, with allowances made for dip, refraction, etc. 
 (See Eighty-Nine-Forty-Eight.) 
 
 Sun. — If the altitude of the sun's lower limb is measured, the 
 semidiameter (Nautical Almanac) must be added, but if the 
 upper limb is observed, the semidiameter must be subtracted, 
 in order to obtain the altitude of the sun's centre from the hori- 
 zon. For practical purposes the semidiameter of the sun may 
 be called 16'. 
 
 Parallax (Table 16) is always added, because the body appears 
 lower when viewed from the surface of the earth than it would 
 if observed from the earth's centre — except when the body is in 
 the observer's zenith when it has no parallax. 
 
 Dip (Table 14) is always subtracted, as the elevation of the 
 observer's eye above the sea-level causes the navigator to meas- 
 ure too great an altitude. 
 
 Refraction (Table 20) is always subtracted, owing to the body 
 
THE NAVIGATOR'S POCKET-BOOK 41 
 
 being seen above its true place, except when it is in the zenith 
 of the observer, when it has no refraction. 
 
 Moon. — The semidiameter (Nautical Almanac) of the moon 
 and the dip (Table 14) are applied in exactly the same manner as 
 explained for the sun ; but parallax in the case of the moon is 
 large as compared with refraction, and it is so arranged that the 
 moon's parallax (Table 23) is given minus the refraction, so that 
 the figures selected from this table must always be added to the 
 altitude. For practical purposes the semidiameter of the moon 
 may be called 16', the same as the sun. 
 
 Planets — The altitudes of these bodies are corrected for 
 dip (Table 14) and refraction (Table 20) as usual, but the correc- 
 tion for parallax involves a new process. With the planet's hori- 
 zontal parallax (Nautical Almanac) and the observed altitude, 
 find the planet's parallax (Table 17) by applying the first two 
 quantities in their respective columns. The semidiameters of 
 the planets are given in the almanac, and if used must be 
 applied as usual, but it is to be explained that for practical pur- 
 poses the altitude of a planet is never corrected for semidiam- 
 eter and parallax. 
 
 Stars.— The altitudes of the stars are corrected for dip (Table 
 14) and refraction (Table 20) as usual ; they have no apparent 
 diameter or parallax. 
 
 Recapitulation. — Note the following: 
 
 Semidiameter is always added for the lower limb and sub- 
 tracted for the upper limb. 
 
 Parallax is always added. 
 
 Dip is always subtracted. 
 
 Refraction is always subtracted. 
 
 It is to be remembered that the sextant's index error (if it has any) 
 is always to be figured as an altitude correction. (See Sextant.) 
 
42 the navigator's pocket-book 
 
 CORRECTED COURSE.— As a preliminary to working 
 out a ship's position by dead-reckoning, the compass courses 
 that have been sailed are converted into true or geographical 
 courses by correcting them for leeway, deviation, and varia- 
 tion. 
 
 Leeway. — The amount is determined as explained under the 
 head of Leeway, and this quantity is allowed to leeward of the 
 compass course. For example, if the course sailed was east 
 and the vessel was on the starboard tack making one point of 
 leeway, the same must be allowed toward the north, making the 
 so far corrected course east- by-north. 
 
 Deviation. — Westerly deviation must be allowed away from 
 the compass course in a direction contrary to the way that the 
 hands of a watch revolve. For instance, if the course after be- 
 ing corrected for leeway is east-by-north, and there is one point 
 of westerly deviation to be considered, the same must be allowed 
 toward the north, making the correct magnetic course east- 
 northeast. On the other hand, easterly deviation will be al- 
 lowed away from the compass course in a direction the same 
 as the hands of a watch revolve. To illustrate : if the course is 
 east-by-north, and there is one point of easterly deviation to be 
 considered, the same must be allowed toward the east, making, 
 in this case, the course east. 
 
 Variation.— This is allowed in exactly the same way as 
 explained for deviation, as will be seen following : we will say 
 that the compass course after being corrected for leeway and 
 deviation is east-north-east, and that there is one point of west- 
 erly variation to be considered. In this case the true or geo- 
 graphical track that the ship has made is northeast-by-east. 
 
 Again, suppose that the compass course after being corrected 
 for leeway and deviation is east, and that there is one point of 
 
THE NAVIGATOR'S POCKET-BOOK 43 
 
 easterly variation to be considered. In this case the true or 
 geographical track that the ship has made is east- by -south. 
 
 Remarks. — When the variation and deviation are of the same 
 name (both east or both west) they may be added together and 
 applied. 
 
 If the variation and deviation are of contrary names they may 
 be subtracted one from the other and the balance applied in the 
 name of the greater of the two quantities. 
 
 It is to be explained that leeway made on the starboard tack 
 is applied in the same direction as westerly variation and devia- 
 tion, and that leeway made on the port tack is applied in the 
 same direction as easterly variation and deviation ; consequently 
 there are times when the three quantities of leeway, variation, 
 and deviation may be added together and applied as a whole to 
 a compass course. 
 
 CORRECTED LOCAL TIME.— To ascertain the correct 
 local time at the ship, proceed as follows : to the sun's time 
 shown by the ship's clock (set when the sun crossed the ship's 
 meridian) add four minutes for every degree of longitude sailed 
 east since the clock was last set, but subtract four minutes for 
 every degree sailed west ; the answer will be the local apparent 
 time at ship. 
 
 COURSE AND DISTANCE.— (See Chart Sailing ; Great- 
 Circle Sailing ; Mercator's Sailing ; Middle Latitude Sailing.) 
 
 COURSE MADE GOOD.— The bearing of the vessel from 
 the latitude and longitude last determined, irrespective of the 
 traverse sailed. (See Dead-Reckoning.) 
 
 COURSE PROTRACTOR.— This consists of a half circle of 
 thin horn or isinglass, having its circular edge graduated into 
 degrees, and a long thread leading from the centre of the instru- 
 
44 the navigator's pocket-book 
 
 ment. To ascertain the course by tliis little contrivance place 
 its zero line on any convenient meridian on the chart, then slide 
 it up or down on this true north and south line until the thread 
 lies in a straight line over the position of the ship and the place 
 sought. The course between the two points will be indicated in 
 degrees on the circle by the direction of the thread. 
 
 Remarks. — The course protractor always gives the true or 
 geographical course, to which must be allowed the variation of 
 the compass for the locality of the ship in order to convert it into 
 a magnetic course. If deviation exists for the compass course 
 found, then this quantity must also be applied. (See Chart 
 Sailing.) 
 
 CROSS-BEARINGS.— (See Chart Sailing.) 
 
 CULMINATE. — When a heavenly body crosses the meridian 
 of the observer it is said to culminate. Upper culmination is 
 when a heavenly body crosses the meridian above the pole, 
 and lower culmination is when it crosses the meridian below 
 the pole. What is known as a moon-culminating star is one that 
 comes to the meridian at the same time with the moon. 
 
 CURRENT. — A progressive motion of the water of the sea at 
 a certain place ; an ocean river. The flow of a current is named 
 according to the direction in which it sets, hence a northeast 
 current comes out of the southwest and flows toward the 
 northeast. (See Patent Log.) 
 
 CURRENT LOG.— Same as ground log, which see. 
 
 CURRENT SAILING. — When a vessel experiences a cur- 
 rent, the effect is to set her in the direction of its flow. This 
 must be considered as a regular and separate course, and the 
 hourly velocity of the current is to be taken as the rate of speed 
 made on such course, as shown following : 
 
THE NAVIGATOR'S POCKET-BOOK 45 
 
 Example. — A ship while sailing southeast enters the Gulf 
 Stream at a point where it is flowing northeast at the rate of two 
 knots per hour, and remains in the stream ten hours. This data 
 is recorded in the log-book, and when working out the dead- 
 reckoning this course of northeast must be entered on the trav- 
 erse table, and the distance of twenty miles considered as the 
 number of knots sailed on that course. 
 
 Remarks. — The chart will give the flow of the current either 
 as true or magnetic. If the former, no correction is to be ap- 
 plied to it after entering it on the traverse table ; but if the latter, 
 then the variation must be applied in order to convert it into a 
 true course. The deviation of the compass never enters into 
 this consideration, because the direction is given by the chart. 
 (See Patent Log.) 
 
 CUT. — When referring to the graduation of the sextant arc, 
 it is said to be cut to ten minutes (10'), and the vernier is said to 
 be cut to ten seconds (10"). 
 
 CYCLONE— (See Law of Storms.) 
 
 DANGER ANGLE— (See Chart Sailing.) 
 
 DANGER-ANGLE TABLES.— Tables that give by mere 
 inspection the distance of a vessel from a certain object. In this 
 consideration the known height of the lighthouse and the verti- 
 cal angle of the same measured to the surface of the water are all 
 that is required for the navigator to ascertain his distance from 
 the object. The danger-angle tables found in the back of this 
 book have been arranged by the author to the nearest 10" of arc 
 (that being the lowest graduation shown on sextants) and extend 
 from thirty feet to three hundred and twenty feet. The manner 
 of using these tables is explained under the head of Chart Sail- 
 ing. To determine the distance of a vessel from a lighthouse 
 
46 THE NAVIGATOR'S POCKET-BOOK 
 
 when beyond the limit of the figures in the danger-angle tables, 
 the " Distance" table in the back of this book may be employed. 
 
 DARKS. — Having reference to those nights during which the 
 moon is not seen in the heavens. 
 
 DAY. — (See Astronomical Day ; Circumnavigator's Day ; 
 Gained Day ; Lost Day ; Lunar Day ; Sea Day ; Sidereal Day ; 
 Solar Day.) 
 
 DAY'S WORK.— The calculation of the ship's latitude and 
 longitude by dead-reckoning. 
 
 DEAD-RECKONING.— The position of the ship found by 
 referring the true courses to the nautical tables and selecting for 
 each course the respective amounts of latitude and departure, 
 then applying the aggregate value of these to the latitude and 
 longitude left. The manner of converting compass courses into 
 true or geographical courses is explained under the head of 
 Corrected Course. 
 
 To Find the Latitude and Longitude. — Convert the compass 
 courses sailed into true or geographical courses by applying the 
 leeway, deviation, and variation. With the distance made on 
 each course, find separately (Table 1 or 2) the difference of lati- 
 tude and departure. After selecting for all, foot the columns of 
 the traverse table, and if both northing and southing have been 
 made subtract one from the other ; also if both easting and west- 
 ing have been made subtract one from the other. 
 
 Apply the difference of latitude to the latitude left, adding 
 the same if the ship has sailed toward the poles, but subtracting 
 if the ship has sailed toward the equator ; the answer will be the 
 latitude by dead-reckoning. 
 
 Next turn to the page (Table 2) marked with the degrees of the 
 middle latitude, apply the departure in the latitude column (read- 
 
THE NAVIGATOR'S POCKET-BOOK 47 
 
 ing from top of page if the degrees of the middle latitude were 
 found there, but from the bottom if the degrees were found 
 there), and opposite to the left in the distance column will stand 
 the difference of longitude. Apply this latter to the longitude 
 left, adding the same if the longitude has been increased, but sub- 
 tracting if the longitude has been decreased ; the answer will be 
 the longitude by dead-reckoning. 
 
 To Find the Course and Distance. — With the difference of 
 latitude and departure, make them compare (Table 2) in their 
 respective columns opposite each other, and in the distance 
 column to the left will be seen the distance in nautical miles 
 made good, and the true or geographical bearing (called course 
 made good) of the vessel from her former calculated position 
 will be read in degrees from the top of the page if the difference 
 of latitude is greater than the departure, but from the bottom of 
 the page if the departure exceeds the difference of latitude. 
 
 Remarks. — If the vessel has been sailing in a current, or has 
 been hove-to, or has taken farewell from the land, these are con- 
 siderations for the traverse table. (See Current Sailing ; Depart- 
 ure ; Drift.) 
 
 Sailing-vessels steer by quarter points, but steamships steer by 
 degrees, consequently in the former sailing, Table 1 is employed, 
 and in the latter sailing Table 2 is made use of. 
 
 To select the difference of latitude and departure, apply the 
 distance sailed on the particular course in the column marked 
 " Dist." in the tables, then read the figures in the two right- 
 hand columns. If the course was found at the top of the page 
 the latitude and departure must be read from the top ; but if 
 the course was found at the bottom of the page the latitude and 
 departure must be read from the bottom. 
 
 DECLINATION.— The angular distance of a heavenly body 
 
48 the navigator's pocket-book 
 
 north or south of the equinoctial. Declination may be expressed 
 as celestial latitude. The declinations of the sun, moon, planets, 
 and stars are to be corrected as explained following : 
 
 Sun.— Select from the Nautical Almanac the sun's declination 
 for Greenwich noon of the Greenwich date, and correct this for 
 the hourly difference of declination by multiplying the latter 
 by the number of hours that the chronometer showed before or 
 past noon at Greenwich at the time the altitude was measured, 
 and either add this correction to or subtract it from the declina- 
 tion given for Greenwich noon, according as the declination is 
 increasing or decreasing. The idea is to ascertain the distance 
 of the sun north or south of the equator at the time of observa- 
 tion. (See Inclination.) 
 
 Moon. — Convert into astronomical time and date the Green- 
 wich time shown by chronometer when the moon's altitude was 
 observed, calling the hours numerically from one to twenty-four 
 instead of referring to them as a.m. and p.m. For example, 
 if, when the observation was taken, the chronometer showed 
 Greenwich civil time November 5th, 8 p.m., both date and hour 
 would be astronomical, and would stand as such ; but if the 
 chronometer showed Greenwich civil time November 5th, 2 
 a.m., then call the astronomical date November 4th and the time 
 fourteen hours. (See Astronomical Time.) 
 
 Now turn to the Nautical Almanac, and under the astronomical 
 date and opposite the astronomical hour select the moon's dec- 
 lination given. Opposite to this to the right will be seen the 
 moon's change of declination for one minute of time. Multiply 
 this minute difference by the number of minutes over the even 
 astronomical hour, and if the moon's declination is increasing 
 add the correction to the declination given for the hour ; but if 
 the moon's declination is decreasing subtract the correction. 
 
THE NAVIGATOR'S POCKET-BOOK 49 
 
 Planets. — The declination of a planet is given for Greenwich 
 noon, and must be corrected in precisely the same manner as 
 described for the sun— the hourly difference of the planet's dec- 
 lination being multiplied by the number of hours shown from 
 Greenwich noon by the chronometer at the time of observation, 
 and this correction either added to or subtracted from the dec- 
 lination of the planet given for Greenwich noon, according as 
 the planet's declination is increasing or decreasing. 
 
 Sta- s. — The declinations of the stars being practically a fixed 
 quantity, no correction is necessary for the declinations given 
 for those bodies— accepting the declinations for the given year 
 as shown in the Nautical Almanac being all-sufficient. 
 
 DEGREE.— The 380th part of the circumference of a circle. 
 The value of a degree is 60'. A degree of latitude is equal to 
 sixty nautical miles or knots, anywhere from the equator to the 
 poles ; but a degree of longitude is equal to sixty nautical miles 
 only on the equator. Leaving the equator, the distance between 
 the meridians constantly contracts, so that at the poles there is 
 no such thing as longitude, all the meridians meeting at those 
 points. If it is desired to learn the distance between any two 
 meridians on a certain parallel of latitude, simply open the 
 nautical tables (Table 2) at the page marked with the parallel in 
 question, then opposite the figures 60 in the distance column 
 will be found (to the right) in the latitude column the number 
 of miles between the meridians. 
 
 Examples. — On the parallel of 40° the distance between the 
 meridians is forty six nautical miles or knots ; consequently, if 
 the ship started from the longitude of 74° and sailed forty-six 
 nautical miles east on the parallel of 40°, she would reach the 
 longitude of 73°. 
 
50 THE NAVIGATOR'S POCKET-BOOK 
 
 On the parallel of 47° the distance between the meridians is 
 40.9 (forty and nine-tenths) nautical miles. 
 
 DEMAGNETIZED COMPASS.— A compass the needle of 
 which has parted with its magnetism. 
 
 DEPARTURE. — The amount of easting or westing made by 
 a vessel from a certain point. To "take departure" is to ob- 
 serve the bearing of and calculate the distance of the vessel from 
 a lighthouse or other point when the harbor is cleared and the 
 first course set. This is also known as "taking farewell." 
 
 Example. — Departure is taken, Sandy Hook light bearing 
 west by compass, distant six miles. This is entered as a mem- 
 orandum in the column of remarks in the log-book, and when 
 working up the dead-reckoning the navigator must set down in 
 the traverse table, as a regular compass course and distance 
 sailed by the ship, east, six miles. The latitude and longitude of 
 Sandy Hook light being accepted as a point of farewell, the 
 opposite point to the bearing of the light and the distance from 
 it must be considered as having been sailed ; otherwise the ship 
 would be six miles out in her dead-reckoning. 
 
 This course of east must be corrected for the deviation of the 
 compass for the ship's head (if deviation exists), also for the 
 variation of the compass given by the chart for the locality of 
 the vessel ; this will convert it into a true or geographical course. 
 (See Corrected Course.) 
 
 DEVIATION.— (See Compass ; Amplitude ; Azimuth ; Cor- 
 rected Course.) 
 
 DIP. — A heavenly body is understood to dip when it disap- 
 pears below the horizon. When a heavenly body crosses the 
 meridian of the observer the limb of its image, as viewed in the 
 
THE NAVIGATOR'S POCKET-BOOK 51 
 
 sextant-glass, will drop below the horizon line, and under such 
 conditions it -is said to dip. (See Dipping Needle.) 
 
 DIP OF THE HORIZON.— As the observer's eye is natu- 
 rally above the sea-level, the limit of view is called the visible or 
 apparent horizon, and the angle between this and the sensible 
 horizon is called the dip of the horizon, which is further ex- 
 plained under the head of Corrected Altitude. 
 
 DIPPER. — The seven stars forming the constellation of the 
 Great Bear, and by means of which the Pole Star, in the tail of 
 the Little Bear, can be readily found. 
 
 DIPPING NEEDLE.— A magnetic needle suspended at its 
 centre of gravity so as to move freely from the horizontal to the 
 perpendicular. On the magnetic equator the needle assumes 
 the horizontal, but at the magnetic poles it stands perpendicular 
 or has a dip of 90°. 
 
 DISTANCE TABLES.— Tabulated distances at which ob- 
 jects can be seen at sea according to their respective elevations, 
 combined with the height of the observer's eye above the sea- 
 level. A distance table will be found in the back of this book. 
 ^See Danger- Angle Tables. ) 
 
 DIURNAL.— Relating to the day. 
 
 DIURNAL ARC. — The half circle described by a heavenly 
 body from its rising to its setting. (See Nocturnal Arc.) 
 
 DIVIDERS.— An instrument consisting of two pivoted legs, 
 used by navigators for measuring distance on a chart, pricking 
 off positions, etc. 
 
 DOMESTIC NAVIGATION.— Generally refers to inland 
 sailing. 
 
52 the navigatok's pocket-book 
 
 DOUBLE ALTITUDE PROBLEM. — (See Sumner's 
 Method.) 
 
 DOUBLE STAR. — Two stars appearing so close together 
 that they seem to touch. 
 
 D. R. — Letters employed to express the word dead-reckoning. 
 
 DRIFT. — When a ship is hove-to she will continually come 
 up and fall off. The middle point between this coming up and 
 falling off must be considered as her compass course, and the 
 leeway, deviation, and variation applied to this compass course 
 in order to obtain the true or geographical track of the ship. 
 
 Example. — A ship is hove-to on the starboard tack ; her head 
 comes up to east and falls off to east-northeast; leeway, four 
 points ; deviation of the compass, one point westerly; variation 
 of the compass, one point westerly. 
 
 Now the middle point between east and east-northeast is east- 
 by-north, and to this we apply the leeway, which gives us 
 northeast-by-north. Next we apply the deviation and variation, 
 and obtain for the true or geographical course of the ship north- 
 b} r -east. 
 
 DRY COMPASS. — A compass card enclosed in an air-cham- 
 ber, commonly referred to as a dry-card compass. (See Liquid 
 Compass.) 
 
 DUMB COMPASS. — A circle of brass or other substance 
 having engraved or printed on it the points of the compass. 
 
 EARTH. — The third planet in order of distance from the sun ; 
 equatorial diameter, 7,926 miles ; polar diameter, 7,899 miles. 
 The difference between the two diameters (twenty-seven miles) 
 is called the compression. Surface, one hundred and ninety- 
 seven millions of square statute miles, of which fifty-one mill- 
 ions is land ; mean distance from the sun, ninety-five millions 
 
THE NAVIGATORS POCKET-BOOK 53 
 
 of miles ; circumference at the equator, about twenty-five thou- 
 sand miles ; inclination to the plane of the ecliptic, 23£°. 
 EARTH'S INDUCTION.— (See Magnetic Induction.) 
 EIGHTY-NINE-FORTY-EIGHT. — In working latitude 
 some navigators lump the correction for the lower limb of the 
 sun as a constant plus 12' quantity, and simply add this amount 
 to their observed altitude in order to obtain the central altitude 
 of the body. They then subtract the latter from 90°, as usual, 
 to find the zenith distance. Others adopt a still shorter method 
 for obtaining the zenith distance : instead of adding 12' to their 
 observed altitude they subtract the observed altitude from 89 D 
 48' (which is 12' less than 90 r ), which at once gives the zenith 
 distance. This twelve-minute or eighty-nine-forty-eight meth- 
 od is liable to make an error of several miles in the answer to 
 the problem when the height of eye correction (dip) is large, 
 such as it would be on the deck and bridge of a vessel with a 
 high freeboard. Altitudes should always be corrected as ex- 
 plained under the head of Corrected Altitude. 
 
 ECLIPTIC— The apparent path of the sun around the earth, 
 but the earth's real path. (See Inclination.) 
 
 ELEVATED COMPASS.— A masthead or a pole compass 
 raised above the deck for the purpose of getting it beyond the 
 magnetic influence of the ship's iron and machinery. 
 
 ELEVATED POLE.— The pole which is above the horizon. 
 The elevation of the pole is the altitude of the pole above the 
 true horizon, and it is equal to the latitude of the place. 
 
 EPHEMERIS. — An unabridged astronomical almanac. 
 
 EPITOME. — An abridged treatise, such as an epitome of 
 navigation. 
 
54 the navigator's pocket-book 
 
 EQUAL ALTITUDES.— (See Longitude.) 
 
 EQUATION OF TIME.— The difference between mean and 
 apparent time. The equation of time selected from the Nautical 
 Almanac for Greenwich noon of the given Greenwich date must 
 always be corrected for the number of hours shown from Green- 
 wich noon by the chronometer when the altitude of the heavenly 
 body was measured. 
 
 Rule. — Select from the Nautical Almanac the equation of time 
 for the given Greenwich noon, also the hourly difference of 
 equation, and multiply the latter by the number of hours shown 
 from Greenwich noon by the chronometer when the observation 
 w r as taken ; then either add this correction to or subtract it 
 from the equation given for Greenwich noon, according as the 
 equation of time is increasing or decreasing. The idea is to 
 find the equation of time for the hour of observation. (See 
 Mean Sun.) 
 
 EQUATOR. — The imaginary line encircling the earth, equi- 
 distant 90° from the north and south poles. 
 
 EQUINOCTIAL The celestial equator. 
 
 EQUINOCTIAL POINTS.— (See First Point of Aries.) 
 
 EQUINOX. — (See Autumnal Equinox ; Vernal Equinox.) 
 
 ERROR OF COLLIMATION.— (See Axis of Collimation.) 
 
 EVENING STAR.— (See Morning Star.) 
 
 EX-MERIDIAN.— (See Latitude.) 
 
 FARE WELL.— (See Departure. ) 
 
 FATHOM.— (Six feet.) 
 
 FINDING THE TIME.— (See Regulating.) 
 
THE XAYIGATOR S POCKET-BOOK 00 
 
 FIRST MERIDIAN,,— (See Prime Meridian ; Circumnavi- 
 gator's Day.) 
 
 FIRST POINT OF ARIES.— That point of the ecliptic 
 which the sun crosses on March 21st from the south to the 
 north side of the equator. The point of the ecliptic which the 
 sun crosses on September 23d from the north to the south 
 side of the equator is known as the First Point of Libra. These 
 two points are termed the Equinoctial Points, and when the 
 sun crosses them the lengths of the days and nights are equal 
 throughout the world. The First Point of xAries is the Spring 
 (or Vernal) Equinox, and the First Point of Libra is the Au- 
 tumnal Equinox. 
 
 FIRST POINT OF CANCER— That point of the ecliptic 
 which the sun enters about June 21st, when its declination is 
 23^° north. 
 
 FIRST POINT OF CAPRICORN. — That point of the 
 ecliptic which the sun enters about December 21st, when its 
 declination is 23|° south. 
 FIRST POINT OF LIBRA.— (See First Point of Aries.) 
 FIXED STARS.— The term "fixed stars" applies to those bod- 
 ies in the heavens which appear constantly in the same relative 
 position. The fixed stars shine by their own light, and their ap- 
 parent twinkling and their smaller appearance distinguish them 
 from the planets. The planets are seen sometimes in one posi- 
 tion and sometimes in another, the same planet being at one 
 time the morning star and at another time the evening star. The 
 fixed stars are separated into classes, the brightest being stars of 
 the first magnitude, of which it is generally accepted there are 
 nineteen ; the second in order of brightness are classed under 
 the head of second magnitude and number about sixty ; next 
 
56 THE navigator's pocket-book 
 
 the third magnitude, numbering about two hundred ; then follow 
 fourth, fifth, and sixth magnitudes, beyond which they cannot 
 be distinguished without the aid of a telescope, consequently 
 such stars are known as telescopic stars. Variable stars are those 
 which appear to intermit in the way of brightness, and inter- 
 mediate stars are those which are divided between two magni- 
 tudes, and may be seen expressed as 1-2, meaning that they are 
 nearer 1 than 2 ; but if they are expressed as 2-1, it means that 
 they are nearer 2 than 1. The term magnitude has no reference 
 to the dimensions or masses of the stars, but only to their bright- 
 ness. The word constellation means a group of stars, fanci- 
 fully supposed to represent some figure, such as a classical hero, 
 a beast, bird, fish, etc. The brightest stars were distinguished 
 by the ancient astronomers by proper names, such as Rigel, Sir- 
 ius, etc.; but the commonest practice is to use the small letters 
 of the Greek and Roman alphabets to classify their degrees of 
 brightness, a being prefixed to the brightest, & to the next 
 brightest, and so on. When the Greek letters are exhausted the 
 Roman are made use of, such as a, b, c, d, etc., and when these 
 are also exhausted then numerals are made use of, such as 1, 2, 
 3, 4, etc. 
 
 The following nine stars (Arietis, Aldebaran, Pollux, Regulus, 
 Spica, Antares, Aquilse, Fomalhaut, and Pegasi) are those prin- 
 cipally used by navigators for finding the longitude, and the 
 navigator should not rest satisfied until he has succeeded in so 
 familiarizing himself with those parts of the heavens in which 
 they are placed as to be able to readily refer to them. By fol- 
 lowing the directions given he may soon impress their relative 
 positions upon his memory. 
 
 In the higher northern latitudes if the observer will look 
 toward the north pole he will see (as shown following) a star 
 
THE NAVIGATOR'S POCKET-BOOK 
 
 57 
 
 a Arietis. 
 
 Aldebaran. 
 
 ' Pollux. 
 
 of the second magnitude, called the Pole Star. It 
 is easily recognized because it Las no other star of 
 equal brightness in its immediate vicinity, and be- 
 cause it is always seen in the same direction — bear- 
 ing north. Another distinguishing feature in rela- 
 tion to it is the constellation of the Seven Stars, 
 commonly known as the Dipper, the two stars in 
 the dipper end of which (called the Pointers) point 
 to the Pole Star. 
 
 This star bears about west, distant 23° from the 
 Seven Stars ; it is of the second magnitude, and 
 may be known by means of a star of the third magni- 
 tude, situated southwest from a Arietis, at the dis- 
 tance of 3^°. South from this star, at a distance of 
 H°, is a star of the fourth magnitude. 
 
 About 35° east-southeast from a Arietis, and 14° 
 southeast from the Seven Stars, is the bright star 
 Aldebaran. Near this star to the westward are sev- 
 eral stars of the third and fourth magnitudes, form- 
 ing with Aldebaran the letter V. At the distance 
 of 23° from this star, in a southeast direction, are 
 three very bright stars, situated in a straight line, 
 near to each other, being known as The Belt of 
 Orion. 
 
 At a distance of 45° from Aldebaran, in the di- 
 rection of east-northeast, is the bright star Pollux. 
 Northwest from Pollux, distant 5°, is the bright 
 star Castor. 
 
 East-southeast-half-east from Pollux, at a dis- 
 tance of 37-|°, is the bright star Eegulus. North of 
 
58 THE NAVIGATOR'S POCKET-BOOK 
 
 # # this star, at a distance of 8", is a star of the second 
 
 magnitude, and further to the northward are five 
 
 # stars of the third magnitude, the whole forming a 
 * cluster resembling a sickle, Regulus being the ex- 
 
 Regulus. * tremity of the handle. A line drawn from the 
 Pole Star, through its pointers, will pass about 12° 
 to the eastward of Regulus. 
 
 '""Spica. East-southeast from Regulus, at a distance of 54°, 
 
 * is the bright star Spica, with no other bright star 
 near it. Southwest from this star, at a distance of 
 about 16°, are five stars of the third and fourth 
 
 * * magnitudes, situated as shown in adioinimr figure, 
 
 the two northernmost of which form a straight line 
 with Spica. 
 
 East-southeast from Spica, at a distance of 46°, 
 is the remarkable star Antares, being of a reddish 
 color, so that it is easily distinguishable. On each 
 w Antares. side of it, about 2° distant, is to be found a star of 
 the fourth magnitude, these stars bearing respect- 
 ively from Antares west-northwest and south- 
 southeast. In the vicinity of Antares there is no 
 very bright star. 
 
 Northeast from Antares, at the distance of 60°, 
 
 # is the bright star a Aquilse ; north-northwest of 
 *a Aquilse. w ^ch, at 2° distant, is a star of the third magni- 
 
 % tude, and south-southeast, at 3° distant, is a star 
 
 of the fourth magnitude. These three stars ap- 
 pear practically in a straight line. aAquilaa may 
 be readily distinguished, as it is of a reddish nature, 
 being nearly of the same color as Antares. 
 
Fomalhaut. 
 
 THE NAVIGATOR'S POCKET-BOOK 59 
 
 Southeast from aAquilve, at a distance of 60°, is 
 the bright star Fomalhaut. It is in high southern 
 declination, so that in northern latitudes its altitude 
 is small. On the parallel of 40° north its altitude 
 is about 20°. Fomalhaut bears nearly south from 
 j4 the star a Pegasi, being about 45° distant. A line 
 drawn from the pointers in the Dipper, through the 
 Pole Star, and continued to the opposite meridian, 
 will pass very near to a Pegasi and Fomalhaut. 
 
 East-by-north from a Aquilse, at a distance of 48°, 
 
 * and westward from aArietis, at a distance of 44°, 
 
 * is the star a Pegasi, which may be distinguished by 
 
 means of four stars of varying magnitudes, situated 
 
 * as shown in the adjoining figure. The star due 
 
 north of a Pegasi is of the second magnitude, and 
 
 ■fc a Pegasi. is distant 13°. The two close stars northwest of 
 
 a Pegasi point to this star, and the most northern 
 
 one of the two close stars is in line with a Pegasi 
 
 and the most northern and western star in the 
 
 group. 
 
 Remarks. — To reconcile compass directions with the fore- 
 going star diagrams, the navigator must hold the page upside 
 down over his head, directing the top of the page toward the 
 north. 
 
 FOCAL DISTANCE. — The distance between the object-glass 
 and the image. Focal length means the same as focal distance. 
 
 FOUR-POINT BEARING.— (See Chart Sailing.) 
 
 FURLONG. — An eighth of a mile ; == forty rods ; — two 
 hundred and twenty yards ; — six hundred and sixty feet. 
 
60 THE NAVIGATORS POCKET-BOOK 
 
 GAINED DAY.— (See Circumnavigator's Day.) 
 
 GEOGRAPHICAL MILE.— A nautical or sea mile of 
 6,082.66 feet ; the mean length of a minute of latitude ; a knot. 
 
 GEOGRAPHICAL POLES.— The extremities of the earth's 
 axis ; the two points of 90° north and south. 
 
 GRADUATED. — Divided ; a scale, as, for instance, the grad- 
 uated arc of a quadrant, octant, and sextant, or a graduated 
 vernier. 
 
 GRADUATED RULES.— Parallel rules having one of the 
 bevelled edges divided into degrees and the other edge divided 
 into quarter points of the compass. They are used for shaping 
 a course and are independent of the diagram compasses on the 
 chart. 
 
 Rule. — Lay the rules on the chart on the course to be deter- 
 mined so that the centre mark of the rules rests on a meridian 
 line, and read the true course on the divided edge where it is cut 
 by the meridian line. This true course must always have the 
 variation of the compass for the ship's locality applied to it in 
 order to convert it into a correct magnetic course ; and provided 
 deviation of the compass exists, this quantity must also be taken 
 into consideration. (See Chart Sailing.) 
 
 GREAT-CIRCLE CHART.— (See Chart.) 
 
 GREAT-CIRCLE SAILING.— A straight course between 
 two places is the arc of a great circle. A great-circle track 
 drawn on a Mercator's chart represents a curve, except on the 
 meridians and on the equator, which are great-circle tracks of 
 themselves. According to a great-circle track plotted on a 
 Mercator's chart a ship in following it would constantly change 
 the direction of her head, but in reality she would sail in a 
 
THE NAVIGATOR'S POCKET-BOOK 61 
 
 straight line. This is to be explained by stating that a Merca- 
 tor's chart gives a distorted view of the earth's surface. 
 
 When a vessel, as in the case of a steamship, is navigated on 
 a straight-line course on a Mercator's chart her head is never 
 pointed in the exact direction of the port to which she is bound 
 until that port heaves into sight ; but when following a great- 
 circle track her head is from first to last pointed direct for her 
 destined port. In other words, when a vessel is navigated on a 
 straight line course on a Mercator's chart, her head at starting 
 points toward the equatorial side of the port bound to, and 
 gradually, as the voyage progresses, her head turns in the right 
 direction, or toward the point of her destination ; whereas the 
 great-circle track leads direct from one port to the other. 
 
 As well as shortening the distance between two places, the 
 great-circle track is of the highest importance for sailing ships, 
 as it often happens that a more or less head wind according to a 
 Mercator's course is made a fair wind on a great-circle course. 
 The real direction of the port bound to can only be ascertained by 
 consulting the great circle, and this determines whether the exist- 
 ing wind is fair or ahead for the great-circle course. 
 
 To illustrate the foregoing theory the author shows the follow- 
 ing example, given by Captain S. T. S. Lecky, in his masterly 
 digest of navigation entitled "Wrinkles." It proves the possi- 
 bilities of the great-circle track for sailing vessels : 
 
 Example. — "Take, for instance, the case of a vessel bound 
 from Quebec to Greenock or Liverpool. The true course and 
 distance by Mercator's chart from Belleisle Light -house to Inish- 
 trahul Light-house is N. 83° E., 1,722 miles ; but the distance on 
 the great circle is 1,690 miles, or thirty-two miles less; whilst 
 the course at starting is N. 63|° E. , or 19^° more to the north- 
 ward. Now if a sailing ship on clearing the Strait has the wind 
 
62 the navigator's pocket-book 
 
 at east-half -north, it would at first seem immaterial on looking 
 at Mercator's chart which tack she was put upon ; but if placed 
 on the starboard tack she would lie up within 3^ points of the 
 true direction of her port, whilst if placed on the other tack, 
 instead of approaching her port she would be actually going 
 away from it." 
 
 To Draw the Great-Circle Track.— Professor Airy's exceed- 
 ingly simple and valuable table for sweeping an arc of a great 
 circle on a Mercator's chart on one side of the equator is given 
 following, and is heartily indorsed by the author of this volume. 
 
 Join the place of the ship and the place of destination by a 
 straight line and find the middle point. 
 
 Draw from this middle point a perpendicular line toward the 
 equator and continue the line beyond the equator if found neces- 
 sary in order to sweep the arc. 
 
 With the middle latitude between the two places enter the 
 following table and take out the " corresponding parallel." 
 
 The resting-point for the sharp leg of the pencil-point dividers 
 will be the intersection of the corresponding parallel with the 
 perpendicular line. Place the sharp point of the dividers in 
 this intersection, then with the pencil leg of the instrument 
 sweep an arc that will pass through the place of the ship and 
 the place of destination, and this curved line will be the great- 
 circle track required. 
 
 Changing the Course. — Except on the meridians and on the 
 equator a ship must frequently change her course in order to 
 keep to the great circle. Several points on the arc of the great 
 circle are fixed upon, and these are made Successively by the 
 ship, the course being changed with each point arrived at. 
 These courses will be shaped as usual by the parallel rules and 
 the diagram compasses on the chart, so that in reality a series of 
 
THE NAVIGATOR'S POCKET-BOOK 
 
 63 
 
 
 Corresponding Parallel. 
 
 
 Corresponding Parallel. 
 
 Middle 
 Latitude. 
 
 
 Middle 
 Latitude. 
 
 
 Opposite Name to Lat- 
 
 Same Name as Lati- 
 
 
 itude of Places. 
 
 
 tude of Placss. 
 
 20° 
 
 81° 13' 
 
 * 
 
 # 
 
 22° 
 
 78° 16' 
 
 #• 
 
 * 
 
 24° 
 
 74 c 59' 
 
 * 
 
 * 
 
 26° 
 
 71° 26' 
 
 * 
 
 * 
 
 28° 
 
 67° 38' 
 
 58° 
 
 4° 00' 
 
 30° 
 
 63° 37' 
 
 60° 
 
 9° 15' 
 
 32° 
 
 59° 25' 
 
 62° 
 
 14° 32' 
 
 34° 
 
 55° 05' 
 
 64° 
 
 19° 50' 
 
 36° 
 
 50° 36' 
 
 65° 
 
 25° 09' 
 
 38° 
 
 46° 00' 
 
 68° 
 
 30° 30' 
 
 40° 
 
 41° 18' 
 
 70° 
 
 35° 52' 
 
 42° 
 
 36° 31' 
 
 72° 
 
 41° 14' 
 
 44° 
 
 31° 38' 
 
 74° 
 
 46° 37' 
 
 46° 
 
 26° 42' 
 
 76' 
 
 52° 01' 
 
 48° 
 
 21° 42' 
 
 78° 
 
 57° 25' 
 
 50° 
 
 16° 39' 
 
 80° 
 
 62° 51' 
 
 52° 
 
 11° 33' 
 
 * 
 
 * 
 
 54° 
 
 6° 24' 
 
 * 
 
 * 
 
 56° 
 
 1° 13' 
 
 * 
 
 * 
 
 rhumb lines are employed by the navigator to enable him to 
 keep his ship approximately on the great- circle. 
 
 The sum of the distances sailed on these short courses will 
 not differ much from the distance found for the great circle, 
 provided the points are not too widely spaced. A very prac- 
 tical method employed is to rind the change of course in points 
 of the compass from the starting-place to the middle point on 
 the arc of the great circle, then to turn this number of points 
 
64 the navigatok's pocket-book 
 
 into quarters, and divide the distance of half the circle by the 
 number of quarter points so obtained, which will give the num- 
 ber of miles to sail on each quarter point. 
 
 Example. — Suppose that between the starting-point of the 
 great circle and the middle part of same the change of course 
 is two compass points, and that half of the entire length of the 
 great-circle track is 1,000 miles. Now in two points there are 
 eight quarters, so we divide 1,000 by 8 and get 125 for an an- 
 swer ; consequently we should change the course a quarter of a 
 point for each 125 miles sailed. 
 
 The navigator should bear in mind that the deviation of the 
 compass must be considered in shaping the various courses on 
 the great-circle track. 
 
 Measuring the Distance. — Turn the largest course on the 
 great circle (which will be one of the ends of the arc) into de- 
 grees, and proceed as follows : Select the logarithms, cosecant 
 of the largest course angle, cosine of the smallest latitude, and 
 the sine of the difference of longitude between the two places ; 
 add these three logs together, reject ten in the index, and the re- 
 sult will be the sine of the distance — the degrees of which will 
 be multiplied by 60 to reduce them to miles, and the minutes of 
 the angle added in, and the result will be the distance on the 
 great circle. 
 
 When an angle exceeds 90°, its supplement (what it lacks of 
 180°) may be used, but in this case the sine of the distance should 
 be subtracted from 180°, and the answer multiplied by 60 to 
 obtain the distance. 
 
 Examples. — In the first consideration, with a course of 80° 30', 
 a latitude of 40° 30', and a difference of longitude of 60° 23', 
 we would obtain a distance of 2,525 miles. 
 
 In the second consideration, with a course of 55° 57', a lati- 
 
THE NAVIGATOR'S POCKET-BOOK 65 
 
 tude of 6° 48', and a difference of longitude of 140° 11', we 
 would obtain a distance of 7,793 miles. 
 
 Remarks. — By mere inspection it is possible to at once deter- 
 mine if a great-circle route is practicable — that land, ice, etc., 
 will not interfere. 
 
 Great-circle sailing is valuable only in latitudes beyond the 
 tropics, as within them (23° N. to 23° S.) the difference between 
 the great circle and Mercator's tracks is too small to be consid- 
 ered — within a few degrees of the equator all straight lines 
 drawn on a Mercator's chart practically represent great-circle 
 tracks. 
 
 What is known as Mixed or Composite tracks are modifica- 
 tions of the great-circle track, adopted by reason of obstacles in 
 the way of the latter, such as land, etc. 
 
 When driven a considerable distance from the great-circle 
 track, the navigator should not attempt to regain it, but should 
 trace a new great circle from the place of the ship. 
 
 GREENWICH DATE.— The day of the month at Green- 
 wich. If at any time there should be uncertainty concerning 
 the Greenwich date it may be determined as follows : 
 
 Express the ship's time astronomically (see Astronomical 
 Time), then turn the ship's longitude into time (see Table 7, or 
 Arithmetic of Navigation), and proceed according to one of the 
 two rules given below : 
 
 West Longitude. — Add the longitude in time to the ship's as- 
 tronomical time : their sum, if less than twenty-four hours, will 
 be the Greenwich time of the same date as at ship ; but if their 
 sum is greater than twenty- four hours, reject twenty-four hours 
 and put the Greenwich date one forward. 
 
 East Longitude. — If the longitude in time is less than the 
 ship's astronomical time, subtract the former from the latter, 
 5 
 
66 the navigator's pocket-book 
 
 and call the Greenwich date the same as the ship's date ; but if 
 the longitude in time is greater than the ship's astronomical time, 
 add twenty-four hours to the latter, then subtract, and call the 
 Greenwich date one day less than the ship's date. 
 
 GREENWICH TIME.— The Greenwich hour shown by a 
 chronometer set to that meridian. If the ship's longitude is 
 turned into time (see Table 7, or Arithmetic of Navigation) and 
 added to the local time at the vessel (as shown by the ship's 
 clock), when in west longitude, but subtracted from the local 
 time at ship when in east longitude, the answer wili be the 
 Greenwich time, independent of the chronometer. 
 
 GROUND LOG. — An instrument for detecting the presence 
 of a current when the ship is becalmed on soundings out of 
 sight of land. An ordinary heaving lead is made fast to the 
 regular chip log- line, then the lead is cast overboard and al- 
 lowed to rest on the bottom. If there is a current, the drift of 
 the ship from the lead will at once give its direction by the 
 angle of the log-line, and the velocity of the current will be 
 measured by the seconds glass, or watch, as explained under the 
 heading of Chip Log. 
 
 GUNTER'S SCALE.— A flat rule about two feet in length, 
 marked on one side with the scales of equal parts, chords, tan- 
 gents, sines, etc., and on the other side with the logarithms of 
 these parts. It is employed for solving mechanically certain 
 problems in navigation and surveying. 
 
 HACK WATCH. — A common watch used by navigators, 
 who set it to the time shown by the chronometer, so as to carry 
 the Greenwich time with them on deck when about to measure 
 an altitude. It is also set to the apparent time at ship when ob- 
 
THE NAVIGATOR'S POCKET-BOOK 67 
 
 serving azimuth bearings of the sun for determining the devia- 
 tion of the compass. 
 
 HEAVE OF THE SEA. — When a vessel is sailing more or 
 less in the trough of a heavy sea, the effect is to drive her to 
 leeward, and this is expressed either as the heave of the sea or 
 send of the sea. It goes without saying that a shallow vessel 
 will be lifted off more than a deep vessel, and for that reason no 
 rule can be given, the navigator being obliged from experience 
 to estimate the quantity for his vessel. 
 
 HEELING ERROR.— The change of compass deviation 
 owing to the vessel being listed to port or starboard, and which is 
 compensated by a vertical steel magnet placed exactly under the 
 centre of the compass card. Heeling error will be at its maxi- 
 mum when the vessel is heading north or south, as the north end 
 of the needle will be drawn to the elevated (weather) side. 
 
 HIGH LATITUDE.— Parallels far removed from the equa- 
 tor, both in the northern and southern hemispheres. Opposed 
 to low latitudes, which are parallels in the vicinity of the equator. 
 
 HORIZON. — The apparent meeting of the sea and sky. (See 
 Artificial Horizon ; Dip of the Horizon ; Sensible Horizon ; Vis- 
 ible Horizon.) 
 
 HORIZON GLASS.— (See Sextant.) 
 
 HORIZONTAL DANGER ANGLE.— (See Chart Sailing.) 
 
 HORIZONTAL PARALLAX.— When a heavenly body 
 is on the horizon of the observer, its altitude to him is practi- 
 cally zero, but another observer viewing the body at the same 
 time from the centre of the earth would not see it on his horizon, 
 but elevated above it ; and the difference between these two 
 angles is called the horizontal parallax. 
 
68 the navigator's pocket-book 
 
 HOUR ANGLE.— The angle of a heavenly body at the pole, 
 between the observer's meridian and the circle of declination pass- 
 ing through the body. This angle is measured on an arc of the 
 equinoctial intercepted between the meridian and the circle of 
 declination, and is converted into time by giving to every fifteen 
 degrees (15°) a value of one hour. 
 
 HURRICANE.— (See Law of Storms.) 
 HYDROGRAPHIC CHART.— (See Chart.) 
 
 HYGROMETER. — A wet-bulb thermometer employed by 
 navigators as an adjunct to the barometer and dry-bulb ther- 
 mometer in foretelling weather. This instrument is used to 
 measure the amount of moisture in the air. Two equal ther- 
 mometers are selected and mounted on the same frame, the 
 bulb of one being left naked, while the other is tied up in a thin 
 muslin covering with a cotton wick leading from it to a small 
 cup of water placed beneath it and about three inches away from 
 the wet-bulb thermometer. As the evaporation of the water 
 produces cold, the mercury in the wet-bulb tube will stand lower 
 than its companion the dry bulb, and the depression of the wet- 
 bulb thermometer measures the humidity of the atmosphere. If 
 the water in the muslin which covers the wet bulb be frozen, it 
 will not affect the record, but will give the same reading as 
 though frost did not exist. 
 
 In frosty w r eather, to insure against the muslin becoming dry 
 through evaporation, it should be wetted and allowed some little 
 time to freeze before the reading is made. 
 
 The muslin and wick should so act as to keep the wet bulb 
 always wet so that evaporation may be constantly going on ; 
 and it is recommended that the little muslin bag and wick be 
 
THE NAVIGATOR'S POCKET-BOOK G9 
 
 changed about once a month owing to their tendency to become 
 foul with grit and smoke and dust. 
 When rain, fog, or dew is promised the hygrometer will rise. 
 
 HYPOTHENUSE.— The longest side of a right-angle tri- 
 angle, or the line opposite the right angle. (See Base ; Perpen- 
 dicular.) 
 
 INCIDENCE. — In the artificial horizon the image of a k body 
 is reflected from the surface of the quicksilver to the eye, and 
 the measured angle is always divided by 2 in order to obtain 
 the altitude. This proves at once that the angle of incidence is 
 equal to the angle of reflection. The angle from the body to the 
 quicksilver is the angle of incidence, and the angle from the 
 quicksilver to the eye is the angle of reflection. 
 
 INCLINATION.— The inclination of the plane of the earth's 
 equator to the plane of the ecliptic is about 23° 28' ; this it is 
 that accounts for the declination of the sun. If the axis of the 
 earth was perpendicular to the plane of the ecliptic, the sun 
 would always be on the equator, and in that case the corrected 
 altitude subtracted from 90 c would always be the latitude of the 
 observer as well as the zenith distance of the sun. 
 
 INDEX. — The integer part of a logarithm. (See Sextant.) 
 
 INDEX BAR.— (See Sextant.) 
 
 INDEX ERROR.— (See Sextant.) 
 
 INDEX GLASS.— (See Sextant.) 
 
 INDUCTION.— (See Magnetic Induction.) 
 
 INSTRUMENTAL PARALLAX.— A sextant should always 
 be adjusted by the horizon line at sea and by a distant line (such 
 as the roof of a remote building) on shore, because the horizon 
 and index glasses of the sextant are not on the same horizontal 
 
?0 THE NAVIGATOR'S POCKET-BOOK 
 
 plane. When the horizontal line of a near object is used the 
 sextant cannot be properly adjusted ; but when the horizontal 
 line of a distant object is employed, the instrumental error is 
 practically eliminated. 
 
 INTERCALARY DAY.— A day that is inserted in the cal- 
 endar out of the common order so as to preserve the correspond- 
 ence between the civil and the solar year. The 29th of Febru- 
 ary in a leap year is an intercalary day. 
 
 INTERCARDINAL POINTS.— Northeast, southeast, south- 
 west and northwest points of the compass. 
 
 INTERPOLATION.— To alter by inserting something, as, 
 for instance, reducing the given declination of a heavenly body 
 to another time than that for which it is originally recorded. 
 
 INTERTROPICS.— Between the tropics ; between the par- 
 allels of 23i° north and 231° south. 
 
 INVERTING TELESCOPE.— (See Sextant.) 
 
 IRRADIATION.— The apparent enlargement of the diam- 
 eters of the sun and moon. It is an optical illusion caused by 
 the light of the object, and may be best appreciated in the illus- 
 tration of the new moon — the bright crescent appearing to be a 
 part of a larger circle than that of its shadowed disk. Irradia- 
 tion increases with the brightness of the object, and diminishes 
 in proportion as the illumination of the body and that of the 
 field of view approach equality, vanishing when they become 
 equal. This apparent augmentation is greatest in the case of 
 the sun ; but even in reference to this body the amount of 
 irradiation seldom exceeds 6", so that for all practical purposes 
 the question need not be entertained by the navigator. 
 
 KISS. — When the image of the moon's or sun's limb is made 
 
THE NAVIGATOR'S POCKET-BOOK 71 
 
 to touch the horizon line in measuring an altitude, it is said to 
 kiss the horizon. 
 
 KNOT.— (See Mile.) 
 
 LANDFALL. — To first make the land, to obtain the first 
 view of land when coming from sea. To make what is known 
 as a good landfall signifies that the navigation of the ship has 
 been well performed, and that the exact point of land discovered 
 is the place previously calculated on by the navigator. 
 
 LATITUDE. — The distance of a place on the earth's surface 
 north or south of the equator. Latitude is measured from the 
 equator in degrees, minutes, and seconds. In a degree of lati- 
 tude there are sixty geographical or nautical miles or minutes, 
 each possessing a value of 6,082.66 feet. A mile of latitude 
 and a minute of latitude mean the same thing. The extremities 
 of the earth's axis, the north and south poles, have a value of 
 90°. Latitude may be said to be the angular distance of a place 
 from the equator, measured on a meridian. The following rules 
 furnish the methods for finding the latitude of the ship by 
 observations of the sun, moon, planets, and stars : 
 
 Latitude by the Sun at Meridian. — Observe the altitude (see 
 Altitude) and note the Greenwich hour shown by chronometer ; 
 then correct the observed altitude for index error (if any), semi- 
 diameter, parallax, dip, and refraction (see Corrected Altitude), 
 and always subtract the answer, called the true central altitude, 
 from 90° to obtain the zenith distance, which name the opposite 
 to the bearing of the sun at meridian — i.e., north or south. 
 Correct the sun's declination (see Declination), and if the cor- 
 rected declination has the same name (north or south) as the 
 zenith distance, add the two quantities ; but if they are of 
 different names, subtract the less from the greater, and the an- 
 
72 the navigator's pocket-book 
 
 swer will be the latitude, which will take the name of the great- 
 er quantity. 
 
 Latitude by the Sun— Ex-Meridian. — It sometimes happens 
 that when the sun has climbed, almost to the meridian a passing 
 cloud obscures it and that the body fails to reappear in time for 
 its meridian altitude to be measured, or, on the other hand, 
 there are cloudy days when the sun does not appear in the 
 morning, but bursts through the clouds, temporarily or per- 
 manently, some little time after meridian. Bowditch gives two 
 very useful tables by which the variation of the sun's altitude 
 may be found for thirteen minutes of time on each side of the 
 meridian, which tables are employed according to the following 
 rule : 
 
 Rule. — Observe an altitude (see Altitude) and note the Green- 
 wich hour shown by chronometer, as well as the local apparent 
 time as shown by the ship's clock, which latter correct by add- 
 ing to it four minutes of time for every degree of longitude sailed 
 east since the clock was last set, but by subtracting four minutes 
 for every degree sailed west. Now with this time from ship's 
 noon enter Table 27 and select the figures given. Next with the 
 latitude by dead-reckoning to the nearest degree and the sun's 
 declination to the nearest degree, enter Table 26 and find the fig- 
 ures by which the figures taken from Table 27 must be multiplied. 
 The answer will represent the change of altitude in seconds of 
 arc for the given time from noon, and this result will be divided 
 by 60 to convert it into minutes of arc ; then this is always added 
 to the observed altitude, whether the angle was measured before 
 or after meridian, for in either case the sun was lower than it 
 was at noon. Now correct this augmented altitude for semi- 
 diameter, etc., and proceed precisely the same as described in 
 the preceding rule for a regular meridian sight. 
 
THE NAVIGATOR'S POCKET-BOOK 73 
 
 Remarks. — When the time from noon exceeds the limits of 
 Table 27 (13 minutes), the augmentation of the altitude may be 
 found by simply calculating the square of the given number of 
 minutes, then multiplying same as usual by the figures from 
 Table 26. 
 
 Examples. — If the time from noon is 20 minutes, take out 
 from Table 27 the square for 10 minutes, which is 100 ; multiply 
 this by 4 and the answer will be 400— the square of 20 minutes. 
 Now multiply this 400 by the quantity given in Table 26 for the 
 ship's latitude and the sun's declination, and the answer will be 
 the required correction to be added to the observed altitude. 
 
 If the time from noon is 14 minutes, take out the square of 
 7 minutes, w-hich is 49 ; multiply it by 4, and the answer will be 
 196, the square of 14 minutes, which will be multiplied by the 
 figures from Table 23. 
 
 If the time from noon is 17 minutes, take out the square of 8 
 minutes and 30 seconds, which is 72.2, and multiply it by 4, 
 and the answer will be 288.8, w 7 hich will be multiplied by the 
 figures from Table 26. 
 
 Explanation. — The square of the minutes from noon may also 
 be found in the following easy manner, independent of Table 
 27: 
 
 If the time from noon is 32 minutes, the required square will 
 be found by multiplying 32 by its own number, hence 32 multi- 
 plied by 32 equals 1,024 (32 x 32 = 1,024), which will be multi- 
 plied as usual by the figures from Table 26. 
 
 It must be remembered in using the method of ex-meridian 
 that when the sun passes near the zenith (that is, when its altitude 
 is high) the time from noon at which the observation is taken 
 must not exceed the figures in Table 27. 
 
 The navigator must bear in mind that the latitude found by an 
 
74 the navigator's pocket-book 
 
 ex-meridian observation is the latitude of the ship at the exact 
 time of the sight, and not at 12 o'clock (meridian). To carry this 
 latitude forward or back to noon, it is necessary to apply to it 
 the difference of latitude selected from the Table (1 or 2) for the 
 course and distance made by the ship in the interval between 
 the time of sight and noon. 
 
 Latitude by the Moon at Meridian. — Observe the altitude 
 (see Altitude) and note the Greenwich hour shown by chronom- 
 eter. Correct the latter for its rate (see Rate), also the altitude 
 for index-error (if any), semi-diameter, dip, parallax, and refrac- 
 tion (see Corrected Altitude). Always subtract the answer, called 
 the true central altitude, from 90° to obtain the zenith distance, 
 naming the latter the opposite to the bearing of the moon at 
 meridian — i.e., north or south. Correct the moon's declination 
 (see Declination), and if the corrected declination has the'same 
 name (north or south) as the zenith distance, add the two quan- 
 tities, but if they are of different names, subtract the less from 
 the greater, and the answer will be the latitude, which will take 
 the name of the greater quantity. 
 
 Latitude by a Planet at Meridian. — Observe the altitude 
 (see Altitude) and note the Greenwich hour shown by chronom- 
 eter. Correct the altitude for index error (if any), dip, parallax, 
 and refraction (see Corrected Altitude), and always subtract the 
 answer, called the true altitude, from 90° to obtain the zenith 
 distance, naming the latter the opposite to the bearing of the 
 planet at meridian — i.e., north or south. Correct the planet's 
 declination (see Declination), and if the corrected declination 
 has the same name (north and south) as the zenith distance, add 
 the two quantities, but if they are of different names subtract 
 the less from the greater, and the answer will be the latitude, 
 which will take the name of the greater quantity. 
 
THE NAVIGATOR'S POCKET-BOOK 75 
 
 Latitude by a Star at Meridian. — As the stars are passing 
 the meridian at all hours of the night, it becomes a very simple 
 problem to determine the latitude of the ship when the sky is 
 clear and when the horizon is outlined. In the back of this 
 book will be found star tables which include all the stars of the 
 first magnitude both in the northern and southern hemispheres, 
 and the navigation stars of the second and third magnitudes, to- 
 gether with the astronomical apparent times that they cross the 
 observer's meridian on the first day of each month throughout 
 the year, also their rough declinations. As the times given in 
 the tables for the meridian passages of the stars are calcu- 
 lated astronomically, it must be remembered that from 1 to 
 12 the hours agree with p.m. civil apparent time, but 13 hours 
 means 1 o'clock in the morning, 14 hours means 2 a.m., 20 
 hours means 8 a.m., etc. The declinations of the stars are 
 practically constant, and do not require correction, but the 
 small annual changes of declination are shown in the al- 
 manac. 
 
 The stars come to the meridian four minutes earlier on each 
 successive day, therefore to find the time of a star's meridian 
 passage for any day between the first and last of the month, 
 multiply by 4 the number of days that have passed since the 
 first of the month and always subtract this sum from the time 
 of the meridian passage given for the first. For example, sup- 
 pose that it was required to know the time of the meridian pas- 
 sage of the star Sirius on the 10th of January. The differ- 
 ence between 1 and 10 is 9, so we multiply the latter by 4, and 
 receive 36 for an answer, and this we subtract from the time 
 given for the star's meridian passage on the 1st of January (11 h. 
 50 m.) and obtain 11 h. 14 m., which represents the time that 
 Sirius will cross the meridian of the ship on the 10th day of 
 
76 the navigator's pocket-book 
 
 January. Proceed to find the latitude in the following man- 
 ner : 
 
 Rule. — Observe the altitude (see Altitude) and correct same 
 for index error (if any), dip, and refraction (see Corrected Alti- 
 tude), then always subtract the answer, called the true altitude, 
 from 90° to obtain the zenith distance, and name the latter the 
 opposite to the bearing of the star at meridian — i.e., north or 
 south. Now set the star's declination (given in the almanac) 
 under the zenith distance, and if the} r are of the same name (north 
 or south) add the two quantities, but if thej r are of different 
 names, subtract the less from the greater, and the answer will be 
 the latitude, which will take the name of the greater quantity. 
 
 Remarks. — This star method is the shortest and simplest of 
 all latitude calculations. 
 
 Whenever it is possible the navigator should observe stars both 
 north and south of him (north and soutii of his zenith), then take 
 the mean of the two latitudes obtained, as this will eliminate or 
 halve possible errors in thewa} :r of misjudging the horizon, etc. 
 
 Should the navigator require the time of the meridian passage 
 of a star not contained in either of the star tables in this book, 
 he may calculate it readily by the following method : 
 
 First, select the star's right ascension for the given day from 
 the star page in the back of the Nautical Almanac, also the sun's 
 right ascension from the almanac for the given day of the 
 month. 
 
 Second, if the star's right ascension is less than the sun's right 
 ascension add twenty-four hours to the former, but if not then 
 let it stand as selected. Now subtract the sun's right ascension 
 from the star's right ascension, and the answer will be the astro- 
 nomical apparent time of the star's meridian passage. 
 
 Latitude by the Pole Star at Any Hour. — The following 
 
THE NAYIGATOK's POCKET-BOOK 77 
 
 rule for finding the latitude at any hour of the night by the Pole 
 Star when it is out of the meridian is, to a certain extent, unsat- 
 isfactory, inasmuch as it cannot be depended upon to give the 
 ship's position within two or three miles, although oftentimes 
 with a good horizon the results are quite correct. 
 
 Rule. — Observe an altitude (see xAltitude) at any hour when 
 the star can be seen, and correct the altitude for index error (if 
 any), dip, and refraction (see Corrected Altitude) ; the answer 
 will be the true altitude. To the time shown by the ship's 
 clock when the observation was taken add four minutes for 
 every degree of longitude sailed east since the clock was last 
 set, but subtract four minutes for every degree sailed west. 
 Turn this corrected local apparent time into astronomical time 
 by simply counting the hours from noon to noon in numerical 
 order (1 to 24), instead of dividing them into a.m. and p.m. (see 
 Astronomical Time). To the astronomical time at the ship al- 
 ways add the sun's right ascension from the Nautical Almanac 
 for the given day, and if the result exceeds twenty-four hours 
 then subtract twenty-four hours and apply the remainder (which 
 is called the right ascension of the meridian) in the Pole Star 
 table in the back of this book, and opposite the hours and min- 
 utes will be found a correction which will either be added to or 
 subtracted from the true altitude, according to the given sign ; 
 if + add, if — subtract. The answer will be the latitude, al- 
 ways north, as the star cannot be seen south of the equator. 
 
 Latitude by a Meridian Altitude Below the Pole. — In 
 high latitudes when observing a meridian altitude of a body be- 
 low the pole the altitude will grow less and less until the lowest 
 part of the circle is reached, at which point the body will cross 
 the meridian below the pole, after which it will commence to 
 rise. 
 
78 the navigator's pocket-book 
 
 To find the latitude by a body when it crosses the meridian 
 below the pole, correct the altitude as usual, then obtain the 
 polar distance by subtracting the body's corrected declination 
 from 90°. Now add together the polar distance and the true 
 altitude, and the result will be the latitude. 
 
 Latitude by Dead-Reckoning.— (See Dead-Reckoning.) 
 Latitude by the Artificial Horizon. — (See Artificial Horizon.) 
 LAW OF STORMS.— When a regular wind is so obstructed 
 as to produce a hurricane the wind assumes a rotary motion and 
 extends over an area of from thirty to several hundreds of miles 
 in diameter, revolving with greatest velocity near the vortex. 
 The centre, however, of a hurricane is a space of calm in which 
 frightful and confused seas are to be experienced. In the 
 northern hemisphere these winds revolve contrary to the move- 
 ments of the hands of a clock, and in the southern hemisphere 
 they revolve in the same direction as the hands of a clock. The 
 course or track followed by a hurricane is tolerably definite, as 
 will be seen by the following : 
 
 Track in the Northern Hemisphere. — The cyclone has its 
 origin between the parallels of 10° and 18° north, and advances, 
 or rolls forward, in a general northwesterly direction. Be- 
 tween the parallels of 25° and 30 c it recurves and advances in a 
 general northeaster!}^ direction . From the start and until it breaks 
 up the hurricane spreads out, or increases its diameter, while 
 the wind, to some extent, decreases as the area of the storm 
 widens. West India hurricanes, as a rule, range between the 
 parallels of 10° and 50° north and the meridians of 55° and 85° 
 west, their average rate of progression being three hundred 
 miles a day. 
 
 Track in the Southern Hemisphere. — The cyclone has its 
 origin in the equatorial regions (rarely within 6 C of the equator) 
 
THE NAVIGATOR S POCKET-BOOK 
 
 19 
 
 and advances, or rolls forward, in a general southwesterly direc- 
 tion, and somewhere about the parallel of 25° south it recurves 
 and advances in a general southeasterly direction, increasing 
 in diameter from the start, and finally breaks up. 
 
 Barometer and Weather Indications. — The barometer often 
 rises suddenly just in front of a storm, owing to the air bank- 
 ing up there ; consequently if the general appearance of the 
 weather indicates a storm the rise of the barometer is not to 
 be accepted as evidence that a storm will not be experienced, 
 but rather that one is at hand. The approach of a cyclone 
 may often be foretold by a greenish-tinted sky, a blood-red 
 or bright yellow sunset, a heavy, unaccountable wave-swell, 
 or a thick, lurid appearance of the atmosphere. A restless state 
 of the barometer is another warning. After the ship has entered 
 the storm disk, if a rapid fall of the barometer is experienced it 
 may be accepted as evidence of a violent storm of small diam- 
 eter ; but if a gradual fall of the barometer is noted, then the 
 opposite conditions may be counted on. 
 
 Distance of the Storm Centre. — The following table is given 
 to show the approximate distance that has been calculated for 
 the centre of the cyclone, according to the average fall of the 
 barometer per hour. It is a rough calculation, but it has a 
 certain value : 
 
 Average Fall of Barometer per Hour. 
 
 Distance in Miles from Storm Centre. 
 
 From 0.02 in. to 0.08 in. 
 " 0.06 " 0.08 " 
 " 0.08 " 0.12 " 
 " 0.12 " 0.15 " 
 
 From 250 to 150. 
 
 " 150 " 100. 
 
 " 100 " 80. 
 
 80 " 50. 
 
80 THE NAYIGATOB'S POCKET-BOOK 
 
 Practical Considerations. — The revolving-storm problem, 
 when considered practically as regards the safe navigation of 
 the ship, is simple. First, locate the centre of the cyclone ; 
 second, ascertain the semicircle in which the ship is ; third, 
 determine the direction in which the storm is moving, and 
 decide upon what course to pursue. 
 
 Bearing of the Storm Centre. — Face the wind and note its 
 bearing by compass, then, in north latitudes, count eight points 
 (90°) to the right ; but in south latitudes count eight points to the 
 left of the wind's eye. If the navigator in the northern hemi- 
 sphere has the wind at east, the centre of the cyclone will bear 
 south of him. If a navigator in the southern hemisphere has 
 the wind at east, the centre of the cyclone will bear north of 
 him. 
 
 Semicircles of Storm-Disk. — The storm-disk being divided 
 into two equal parts by the line or axis of the storm track, these 
 two semicircles are named according to the following : Look 
 in the direction toward which the storm is moving, then the 
 portion that lies on the right side of this line is known as the 
 right semicircle, and the portion that lies on the left side is known 
 as the left semicircle. In the right semicircle the wind changes to 
 the right — from north toward east, from east toward south, from 
 south toward west, and from west toward north ; but in the left 
 semicircle the wind changes to the left — from north toward 
 west, from west toward south, from south toward east, and 
 from east toward north. The first change of wind will prove 
 to the navigator the semicircle he is in. 
 
 To Avoid the Centre. — In the northern hemisphere, if the 
 ship is in the right semicircle, haul by the wind on the star- 
 board tack and keep going as long as possible ; but if the ship is 
 in the left semicircle, bring the wind on the starboard quarter, 
 
THE NAVIGATOR'S POCKET-BOOK 81 
 
 note the compass course when the ship is so headed, and keep to 
 that course. In the southern hemisphere, if the ship is in the 
 right semicircle, bring the wind on the port quarter, note the 
 direction of the ship's head by compass, and keep to that course ; 
 but if the ship is in the left semicircle, haul by the wind on the 
 port tack, and keep going as long as possible. 
 
 Tack to Heave-to On. — If obliged to heave-to, act accord- 
 ing to the following simple rule : If in the right semicircle, 
 heave-to on the starboard tack ; but if in the left semicircle, 
 heave-to on the port tack. This rule applies to all parts of the 
 world, and should be impressed upon the navigator's mem- 
 ory. 
 
 On the Storm-Track. — When the ship is on the storm track 
 in front of the centre, she will not experience a change of wind, 
 but will have a falling barometer and constantly increasing se- 
 verity of weather ; but if in the rear of the storm-centre, she will 
 have a rising barometer and a gradual moderation of the weath- 
 er. In the northern hemisphere, if in front of the centre, put 
 the ship before the wind, note the compass course when the 
 ship is so headed, and keep to that course, and if obliged to 
 heave-to do so on the port tack, but if in the rear of the centre, 
 run out with the wind on the starboard quarter, or heave-to on 
 the starboard tack. In the southern hemisphere, if in front 
 of the centre, put the ship before the wind, note the com- 
 pass course when the ship is so headed and keep to that course, 
 and if obliged to heave-to do so on the starboard tack ; but if in 
 the rear of the centre, run out with the wind on the port quar- 
 ter, or heave-to on the port tack. 
 
 Remarks. — When, according to the foregoing rules, a ship is 
 laid-to on the port tack in the left semicircle in the northern 
 hemisphere, and on the starboard tack in the right semicircle in 
 6 
 
82 the navigator's pocket-book 
 
 the southern hemisphere, her head will be directed toward the 
 storm centre. There will be no danger in this, however, as the 
 ship will not head-reach to any extent, consequently she will 
 not approach the storm centre sufficient to amount to anything. 
 Laid-to in this way, she will come up and bow the sea as the 
 wind shifts, whereas if she was laid-to on the opposite tack she 
 would be headed off with every shift of wind, and would ulti- 
 mately bring the sea on the beam and quarter, and would prob- 
 ably founder. 
 
 It has been computed that West Indian cyclones, commencing 
 with a very small diameter, increase the same to six hundred and 
 one thousand miles before breaking up. In the Indian Ocean 
 they spread out from one hundred to six hundred miles, and in 
 the China Sea from eighty to four hundred miles. 
 
 The progressive rate of the West Indian hurricane or cyclone 
 is about three hundred miles a day, and the rate of the Bay of 
 Bengal and China Sea c} T clones, two hundred miles a day ; but 
 the rate of the Indian Ocean cyclone varies from fifty to two 
 hundred miles a day. 
 
 The cyclone season for the West Indies, Atlantic Coast of 
 America, and the coasts of Mexico and Lower California is from 
 July to October. The cyclone season for the Malabar Coast and 
 Bay of Bengal embraces the five months of April and May, 
 October, November, and December. The cyclone season for the 
 China Sea extends from July to November. The cyclone sea- 
 son on the coast of Japan takes in August, September, and 
 October. 
 
 LEEWAY. — The sideways drift of a vessel through the 
 water owing to the pressure of the wind on her spars, sails, and 
 side. Running free, a vessel jnakes no leeway, as all the wind 
 and wave force exerted is on the line of her course ; but the 
 
THE NAVIGATOR'S POCKET-BOOK 83 
 
 closer the ship is hauled to the wind the more she will be forced 
 to leeward. When a steam vessel makes leeway owing to a heavy 
 beam wind and sea, it is recorded in the log-book under the head 
 of "Send of the Sea/' The manner of determining the amount 
 of leeway being made by a vessel is extremely simple : It is 
 only necessary to note the line of the keel by observing the 
 course of the ship, then to see what angle the wake makes with 
 this, and that will give at once the amount of leeway being 
 made. 
 
 Example. — A vessel, we will say, is heading east on the star- 
 board tack ; the heel of her keel is west ; the wake bears by 
 compass west-by-south, consequently the wake makes an angle 
 of one point with the line of the keel, which amount (one point) 
 is the leeway being made. Under these circumstances the ship 
 is really making an east-by-north course. 
 
 Remarks. — If a patent log is being towed, the angle made 
 by the line as compared with the keel will give the amount of 
 leeway. 
 
 Some vessels have a graduated half-circle of brass tacked on 
 the middle of the taff rail, and when desiring to ascertain the 
 amount of leeway, either by day or night, the bight of the log- 
 line is carried to this half-circle and held in the rear centre, then 
 the angle made by the line with the zero point of the circle will 
 give the answer either in degrees or quarter points of the com- 
 pass according as the circle is graduated. 
 
 In case the vessel is not towing a log, the hand-lead may be 
 temporarily thrown overboard and allowed to trail astern, and 
 the angle measured by it, as already explained. 
 
 When the vessel is making no leeway, the wake will be left 
 dead astern, but if leeway is being made, the wake will trend 
 away on the weather quarter. (See Corrected Course.) 
 
84 the navigator's pocket-book 
 
 LEAGUE. — A league is generally conceded to have a value 
 of three nautical miles, but it varies in different countries. In 
 the United States, France, Italy, and England, a league contains 
 6,075 yards ; Spain, 7,416 yards ; Holland and Germany, 8,100 
 yards ; Russia, 8,468 yards. 
 
 LENS. — A piece of glass formed so as to change the direction 
 of rays of light when passing through it, as the magnifying 
 glasses used in telescopes. 
 
 LIMB.— (See Upper Limb.) 
 
 LINE. — A name for the equator. 
 
 LINE OF COLLIMATION.— Same as axis of collimation. 
 
 LINE OF NO VARIATION.— (See Compass.) 
 
 LIQUID COMPASS. — A compass card enclosed and entirely 
 submerged in a chamber of alcohol and water or refined petro- 
 leum, to give steadiness to the card and to prevent it from flying 
 about in a manner peculiar to a dry-card compass when sailing 
 in rough water. 
 
 LOCAL ATTRACTION.— (See Compass.) 
 
 LOCAL APPARENT TIME.— Time calculated by the pas- 
 sage of the sun over the observer's meridian. The length of a 
 solar day varies according to the sun's movement. (See Noon.) 
 
 LOCAL MEAN TIME. — Time calculated by the imaginary 
 passage of an imaginary sun over the observer's meridian. 
 This is known as the mean sun, and is adopted so as to give the 
 civil day a value of exactly twenty-four hours. (See Mean Sun.) 
 
 LOCAL TRANSIT. — The passage of a heavenly body over 
 the meridian of the observer. 
 
 LOG. — To make a memorandum of anything in the log-book 
 is to " log " it. (See Chip Log ; Log-Book ; Patent Log.) 
 
THE NAVIGATOR'S POCKET-BOOK 85 
 
 LOGARITHM. — A logarithm may be defined as the expo- 
 nent of the power to which a given number, known as a base, 
 must be raised in order to produce a certain number. By the 
 employment of logarithms difficult and tedious problems in 
 navigation are so simplified as to be calculated by men whose 
 knowledge of arithmetic does not extend beyond the four com- 
 mon rules of addition, subtraction, multiplication, and division. 
 (Table 44.) 
 
 To Select Logarithms for Degrees and Minutes. — The giv- 
 en number of degrees w T ill be found at the bottom of the page 
 when between 45° and 135°, otherwise at the top. The minutes 
 of the angle must be found in that column marked M, which 
 stands on the side of the page on which the degrees were found. 
 If the degrees are found at the top of page, the sine, cosine, etc. , 
 must be read from the top, but if the degrees are found at the 
 bottom of page, then the sine, cosine, etc., must be read from 
 the bottom. Opposite the given number of minutes will be 
 found the required logarithm. 
 
 To Select Proportions for Seconds.— The proportional parts 
 will be found by the columns of differences for seconds. The 
 correction of the logarithm for any number of seconds is found 
 by entering the left-hand column of the table marked S' at the 
 top, and finding the number of seconds in the regular minute 
 column, and opposite to this in the column of differences will 
 be found the corresponding correction. Thus on the page which 
 contains the log. sines, tangents, etc., for 30°, the corrections for 
 25" are 9 for the columns A. A. ; 12 for the columns B.B., and 3 
 for the columns C.C. ; so that if it were required to find the 
 sine, tangent, or secant of 30° 12' 25" we would add these cor- 
 rections respectively to the logarithms corresponding to 30° 12', 
 because these logarithms increase in proceeding from 30° 12' to 
 
86 THE NAVIGATORS POCKET-BOOK 
 
 30° 13'. If the logarithms decreased from 30° 12' to 30° 13', we 
 
 would subtract this correction. 
 
 To Correct Time for Proportions of Logarithms. — In work- 
 ing a chronometer sight, when selecting the time for the logarithm 
 called ; ' sine of apparent time at ship," if it is impossible to match 
 the logarithm in the column of sine, take the nearest logarithm to 
 it, calculate the difference between the two by simple subtraction, 
 and note the alphabetical sign (A.B. or C.) belonging to the col- 
 umn ; then apply this difference in the little table of correction at 
 the foot of page, opposite the proper letter, and find the correction 
 overhead given in seconds to be added to or subtracted from the 
 time corresponding to the sine accepted. This is done in order 
 to obtain the full value of time for the logarithm " sine of appar- 
 ent time at ship." For example : Should w r e require the p.m. 
 time for the log. sine of 9.70167, we would select the nearest log. 
 to this, which is 9.70159, and find by subtraction that the differ- 
 ence is 8. Now the p.m. time corresponding to 9.70159 is 4 h. 01 
 m. 36 sec, which we note. We now apply the 8 in the foot table 
 opposite the letter A, and find a correction of three seconds over- 
 head, which, in this case, we add to the time selected, making 
 the same 4 h. 01 m. 39 sec. This correction is added because in 
 this instance the time increases as the logarithms increase, and 
 having taken out the time for an inferior log. we must add the 
 correction to obtain the full measure of time for the proper log. 
 
 To Convert Logarithms into Degrees. — Select from the 
 table the degrees and minutes for the next smallest logarithm to 
 the one given, then ascertain by subtraction the difference be- 
 tween them, and with this difference apply it on the same page 
 in the proper "Dif." column, and opposite in the M. column to 
 the left will be given the number of seconds required to complete 
 the degrees, minutes, and seconds. 
 
THE NAVIGATORS POCKET-BOOK 87 
 
 LOG-BOOK. — The log-book is a journal of all that transpires 
 of importance on board ship. Log-books in general use may be 
 described as follows : 
 
 Over the first column is marked the letter H., standing for 
 the hours of the day and night, the figures below it running 
 consecutively from midnight to noon (1 to 12) and then from 
 noon to midnight (1 to 12), making the same divisions of the 
 twenty-four hours as are used on shore. The log-book is kept 
 in civil time now instead of the old method of sea time, as ex- 
 plained under the head of Sea Day. 
 
 Over the next column will be seen the letter K., standing for 
 miles, or as they are nautically called, " knots." 
 
 Next will be seen the letter F., meaning furlongs, a furlong 
 standing for one-eighth of a knot. If the ship had sailed during 
 the watch forty miles and a half, the half knot would be entered 
 as four furlongs. Furlongs are divided by 8 to convert them 
 into miles. 
 
 Following along to the right we next find the word Courses, 
 under which heading, and against the hour, will be noted the 
 course of the ship by the steering compass. Every time the 
 course is changed, the log must be noted, and this reading and 
 the time recorded in the log-book under the proper headings. 
 
 Next is the column of Leeway. In this column is entered the 
 amount of leeway for the respective courses sailed, determined 
 by the officer of the watch. 
 
 The two following columns are for the standing of the Ther- 
 mometer and Barometer. 
 
 The last column is headed Remarks, and under this head will 
 be recorded all matters of importance occurring on board, such 
 as carrying away sails and spars, accidents to crew, work pro- 
 gressing, also meeting with vessels, state of the weather, etc. 
 
88 THE NAVIGATOR'S TOCKET-BOOK 
 
 Half way between midnight and midnight (top and bottom of 
 the page) will be seen the following headings contained in red 
 rulings : Course, Distance, Diff. of Lat., Departure, Lat. by 
 D. R., Lat. by Obs., Variation, Diff. of Long., Long, by D.R, 
 Long by Obs. We will take them up in their order in dealing 
 with them : 
 
 Course. — The bearing of the ship from her former calculated 
 position is entered under this head. This is fully explained 
 under the head of Dead-Reckoning. 
 
 Distance. — On the line of bearing of the ship from the 
 former position the distance is measured in a straight line, and 
 set down. 
 
 Diff. of Lat. — Here is entered the amount of latitude between 
 the position last calculated and the position arrived at accord- 
 ing to dead-reckoning. 
 
 Departure. — In this space is entered the number of departure 
 miles (knots) the ship is either east or west of her place last 
 calculated. 
 
 Lat. by D. R. — By applying the difference of latitude made 
 to the latitude of the ship last determined, we obtain the lati- 
 tude by dead-reckoning, the same being marked under this 
 heading. 
 
 Lat. by Obs. — This is calculated at noon by the sextant, and 
 the result placed in this space. 
 
 Variation. — The variations of the compass on the different 
 courses are shown under this heading. 
 
 Diff. of Long. — The number of minutes of longitude made 
 (estimated by using the middle-latitude as a course in Table 2, 
 and applying the whole departure) are shown under this head. 
 
 Long, by D.R. — The longitude by dead-reckoning is found 
 by applying the difference of longitude made to the longitude 
 
THE XAVIGATOK'S POCKET-BOOK 89 
 
 of the ship last determined, and the same is recorded under this 
 head. 
 
 Long, by Obs. — The longitude by observation at noon (me- 
 ridian) may be calculated by equal altitudes, but, as a rule, the 
 morning position is carried forward to noon and the afternoon 
 position is carried back to noon, in the way explained following : 
 
 To Carry Longitude Forward.— Suppose that we should ob- 
 tain a chronometer sight at 8 o'clock in the morning and 
 determine our longitude at that time. Between the time of this 
 sight and noon four hours elapse, and in order to find our lon- 
 gitude at noon all that it is necessary to do is to correct the 
 course or courses sailed since 8 a.m. ; select the departure from 
 Table 2, turn it into minutes of longitude for the parallel of the 
 ship, and apply this difference of longitude to the longitude of 
 the ship found at 8 o'clock. Of course this will not be exactly 
 the longitude by observation, but it will be so near the truth 
 that for practical purposes it may be considered as the ship's 
 longitude by observation at noon. 
 
 To Carry Longitude Back — Suppose that no observation 
 was secured during the morning, but that a sight was obtained 
 at 4 o'clock in the afternoon. In order to carry the longitude 
 back to noon so as to enter it in its column, we must find the 
 difference of longitude made by the ship since noon, and apply 
 it to the longitude of the ship found at 4 p.m. 
 
 Symbols. — Letters and numbers are sometimes employed in 
 log-books to represent the weather, wind, and sea. The follow- 
 ing shows the various notations : 
 
 Weather is indicated by the small italic letters : b (blue sky), 
 c (detached clouds), d (drizzling rain), /(foggy), g (gloomy), h 
 (hail), I (lightning), m (misty), o (overcast),^? (passing showers), 
 q (squally), r (rainy), s (snow), t (thunder), u (ugly, threatening), 
 
90 THE NAVIGATOR'S POCKET-BOOK 
 
 v (visibility, clearness), w (wet, dew). When a bar ( — ) is placed 
 under a letter it augments its signification, and when a bar and a 
 clot (—) are placed under it, it signifies heavy and continuous 
 weather of the character indicated. 
 
 Wind is denoted by the numerals, (calm), 1 (light air), 2 
 (light breeze), 3 (gentle breeze), 4 (moderate breeze), 5 (fresh 
 breeze), 6 (strong breeze), 7 (moderate gale), 8 (fresh gale), 9 
 (strong gale), 10 (whole gale), 11 (storm), 12 (hurricane). 
 
 Sea swell is indicated by the capital letters, S (smooth), M 
 (moderate), L (long), R (rough), C (cross), H (heavy), V H (very 
 heavy). 
 
 Remarks. — Steamship log-books are ruled slightly different 
 from those of sailing ships, as there is no column heading for 
 leeway ; but instead there are columns for slip of wheel, etc. 
 (See Current Sailing ; Departure ; Drift ; Heave of the Sea ; 
 Slip of Wheel.) 
 
 Watches. — The seven watches of the log-book are named as 
 follows : 
 
 From 8 p.m. to 12 midnight, the First Watch. 
 
 From midnight to 4 a.m., the Mid Watch. 
 
 From 4 a.m. to 8 a.m., the Morning Watch 
 
 From 8 a. m. to noon, the Forenoon Watch. 
 
 From noon to 4 p.m, the Afternoon Watch. 
 
 From 4 p.m. to 6 p.m., the First Dog Watch. 
 
 From 6 p.m. to 8 p.m., the Second Dog Watch. 
 
 The reason for the watch from 8 p.m. to midnight being called 
 the First Watch, is because when a ship puts to sea the first 
 watch is always set at 8 p.m. The captain always stands the 
 first watch out, and the mate stands the first watch coming home. 
 The captain's watch is called the starboard, and the mate's the 
 port watch. 
 
THE NAVIGATOR'S POCKET-BOOK 91 
 
 Note. — Never ditto figures in the log-book, but where the 
 same course and wind are continuous, always employ ditto 
 marks, as it will keep the log-page neater, and make it easier to 
 read. 
 
 LOG-SLATE. — The deck slate on which the officer of the 
 watch keeps a record of the ship's speed, course, etc., and from 
 which the smooth log-book is made up. To enter anything on 
 the slate is to "log" it. 
 
 LONGITUDE. — The distance of a place on the earth's sur- 
 face east or west of some given prime meridian. Longitude 
 is measured in degrees, minutes, and seconds, counting as high 
 as 180° east and 180° west, thus completing the circumference of 
 the globe. The meridian of 180° east and the meridian of 180° 
 west are represented by the same line, so that a vessel may be 
 on both at the same time. Longitude may be defined as the 
 angle at the pole contained between two meridians, one passing 
 through the place in question and the other through some con- 
 ventional point from which longitudes are reckoned. (See 
 Prime Meridian.) The following rules furnish the methods for 
 finding the longitude of the ship by observations of the sun, 
 moon, planets, and stars. 
 
 Longitude by Equal Altitudes of the Sun. — Observe an 
 a.m. altitude (see Altitude) and at the instant of contact note the 
 hour, minute, and second shown by chronometer. When the 
 sun falls to the same altitude after noon, note again the chronom- 
 eter. Add these two times together and divide by 2, then apply 
 the rate correction, and the answer will show the mean time 
 that it was at Greenwich when it was apparent noon at ship. Re- 
 duce this Greenwich mean time to apparent time by applying to 
 it the corrected equation of time (see Equation of Time), and if 
 
92 THE 
 
 the ship is in west longitude simply turn this apparent time into 
 degrees (Table 7), and the answer will be the longitude of the 
 ship ; but if the vessel is in east longitude, the apparent time 
 must be subtracted from 12 hours and the remainder turned 
 into degrees. 
 
 Remarks. — The time may also be converted into degrees by the 
 use of the rule given under the head of Arithmetic of Naviga- 
 tion. 
 
 Observe the first altitude about half an hour before noon. 
 
 If, after measuring the first altitude, the ship sails toward the 
 sun, then the original altitude must be increased one minute of 
 arc for every mile sailed between the two sights. To make this 
 clear, let it be supposed that the first altitude read 20° 30' and that 
 in the interval between the sights the ship sailed ten miles toward 
 the sun — the instrument must be set to read 20° 40' and the sec- 
 ond altitude measured by that. If, on the other hand, the ship 
 sails away from the sun after measuring the first altitude, then 
 the reading must be decreased one minute of arc for every mile 
 sailed in the interval, and the second altitude measured accord- 
 ingly. 
 
 Longitude by One Altitude of the Sun. — Observe an altitude 
 (see Altitude) and note the hour, minute, and second shown by 
 chronometer at the instant of contact, and correct the latter for 
 its rate ; also correct the altitude and the sun's declination (see 
 Rate ; Corrected Altitude ; Declination). Next obtain the sun's 
 polar distance (see Polar Distance) and add to it the true central 
 altitude and the latitude by dead*reckoning, then divide the sum 
 of these three quantities by 2, and from the half sum so obtained 
 subtract the true central altitude, calling the answer the remain- 
 der. Now select (Table 44) the logarithms, secant of the latitude, 
 cosecant of the polar distance, cosine of the half sum, and sine 
 
THE NAVIGATOK'S POCKET-BOOK 93 
 
 of the remainder — rejecting the index of each log. when it is 
 more than 9 (see Logarithm). Add these four logs, together, 
 divide by 2, and the answer will be the sine of the apparent 
 time at ship when the sight was taken. With this sine, select 
 (Table 44) the time standing against it, taking same from the a.m. 
 column if the observation is made in the morning, but from the 
 p.m. column if made in the afternoon. If the log. sine cannot be 
 perfectly matched, then select the time for the nearest corre- 
 sponding log. and correct the time as explained under the head of 
 Logarithms. Apply the corrected equation of time (see Equa- 
 tion of Time) to the apparent time at ship according to the head- 
 ing of the almanac column, so as to convert it into mean time at 
 ship. The difference between the mean time at ship and the 
 mean time at Greenwich will be the longitude in time, which 
 will be turned into degrees either by the use of Table 7 or by the 
 rule given under the head of Arithmetic of Navigation. 
 
 Remarks. — If one time is a.m., and the other time p.m., it will 
 be necessary to add twelve hours to the p.m. time before subtract- 
 ing—for instance, if the time at ship is 10 a.m. and the time at 
 Greenwich 2 p.m., the times are four hours apart, and this is 
 found by calling the Greenwich time fourteen hours and sub- 
 tracting the ten hours from it. 
 
 The best time to take sights for longitude is when the sun is 
 either rising or falling rapidly, so that a considerable change of 
 altitude will only affect the time to a small extent ; but do not 
 use an altitude of less than 10°, owing to the uncertainty of the 
 refraction. 
 
 When the sun can be observed exactly in the prime vertical 
 (when it bears true east or west) an error of a considerable num- 
 ber of miles in the latitude by dead-reckoning will not produce 
 a wrong result in the longitude. (See Prime Vertical.) 
 
94 the navigator's pocket-book 
 
 If it is desired, several altitudes may be observed iD quick suc- 
 cession, noting the corresponding times by chronometer, and the 
 sum of these altitudes and times divided by the whole number of 
 altitudes taken so as to obtain the mean of the altitudes corre- 
 sponding to the mean of the times. This process will eliminate 
 any small error that might creep into a single altitude and 
 time. 
 
 In order to understand the manner in which longitude is car- 
 ried forward or back to noon from an a.m. or a p.m. sight, see 
 explanation given under heading of Log-Book. 
 
 Longitude -at Sunrise or Sunset.— Observe the sun's upper 
 or lower limb to touch the horizon at rising or setting and note 
 the hour, minute, and second shown by chronometer at the in- 
 stant of contact, and correct the latter for its rate ; also correct 
 the sun's declination and obtain the polar distance (see Rate ; 
 Declination ; Polar Distance). Now add together the latitude 
 by dead-reckoning and the polar distance and from their sum 
 subtract 21' if the contact of the lower limb was observed, but 
 subtract 53' if the contact of the upper limb was noted. Now di- 
 vide the balance by 2, and to this half-sum add 21' for a lower- 
 limb calculation, but add 53' for an upper-limb calculation. 
 From this point select the various logarithms and proceed to 
 find the longitude in precisely the same manner as directed in 
 the preceding rule under the head of Longitude by One Al- 
 titude of the Sun. 
 
 Remarks. — The particular value of this working is in the 
 fact that the sextant is dispensed with ; consequently, if that 
 instrument meets with an accident and is rendered useless, the 
 navigator is not left dependent upon his dead-reckoning for 
 longitude. 
 
 By employing a marine glass, the contact of the sun's limb 
 
THE NAVIGATOR S POCKET-BOOK 
 
 95 
 
 with the horizon may be more accurately determined than by 
 the unaided eye. 
 
 Longitude by an Altitude near Sunrise or Sunset. — At the 
 time that the centre of the sun is in the true horizon (90° from 
 the zenith) the lower limb has an apparent altitude of about 19' 
 and the upper limb about 46'. 
 
 A little time before sunrise or sunset, consult the following 
 table and select under the figures most nearly corresponding to 
 the height of eye, the altitude for the sun's lower or upper limb 
 as desired, and place same on the arc of the sextant : 
 
 
 Height of Eye, 13 feet. 
 
 Height of Eye, 21 feet. 
 
 Sun's Semi- 
 diameter. 
 
 Altitude of 
 
 Sun's Upper 
 
 Limb. 
 
 Altitude of 
 
 Sun's Lower 
 
 Limb. 
 
 Sun's Semi- 
 diameter. 
 
 Alt'tude of 
 
 Sun's Upper 
 
 Limb. 
 
 Altitude of 
 
 Sun's Lower 
 
 Limb. 
 
 / // 
 
 / // 
 
 / // 
 
 / // 
 
 / // 
 
 / // 
 
 15 45 
 
 48 00 
 
 18 20 
 
 15 45 
 
 47 00 
 
 19 20 
 
 16 00 
 
 46 10 
 
 18 10 
 
 16 00 
 
 47 10 
 
 19 10 
 
 18 15 
 
 48 20 
 
 18 00 
 
 16 15 
 
 47 20 
 
 19 00 
 
 With the sextant set to the required altitude, note when the 
 image of the sun's proper limb is in perfect contact with the 
 horizon line, and observe the hour, minute, and second shown 
 by chronometer at the instant of kissing. Correct the chronom- 
 eter for its rate (see Rate) and add together the logarithms tarn 
 gent of the ship's latitude (by dead-reckoning) and tangent of 
 the sun's corrected declination (see Declination) ; their sum, re- 
 jecting ten from the index, will be the logarithm sine of an 
 angle, which select from Table 44 and turn into time by Table 7, 
 or by the rule under Arithmetic of Navigation. If the latitude 
 and the sun's declination are of the same name (north or south) 
 add the time so found to six hours at sunset, but subtract it from 
 six hours at sunrise. If the latitude and declination are of con- 
 
96 the navigatob's pocket-book 
 
 trary names, add the given time to six hours at sunrise, but sub- 
 tract it from six hours at sunset. To this apparent time at ship 
 apply the equation of time (see Equation of Time) so as to con- 
 vert it into mean time at ship, after which take the difference be- 
 tween it and the Greenwich mean time and turn the result into 
 degrees, which will be the longitude of the ship. 
 
 Remark. — This method should not be used beyond the par- 
 allels of 40° north and south. 
 
 Longitude by One Altitude of the Moon. — Observe an alti- 
 tude (see Altitude) and note the chronometer at the instant of 
 contact, to which time apply the rate correction, then turn this 
 Greenwich mean time into astronomical mean time (see Astro- 
 nomical Time) and next correct the moon's altitude and declina- 
 tion (see Corrected Altitude ; Declination). Now obtain the 
 moon's polar distance (see Polar Distance) and add to it the 
 moon's corrected altitude and the latitude by dead-reckoning ; 
 divide the sum of these three quantities by 2 and from this 
 half-sum subtract the moon's corrected altitude. Select (Table 
 44) the logarithms secant of latitude, cosecant of polar distance, 
 cosine of the half-sum and sine of the remainder, rejecting the 
 index of each log. when it exceeds nine. Add these four logs, 
 together, divide by 2, and the answer will be the sine of a time 
 which will be selected from the P. M. column (Table 44). Apply 
 this time to the moon's corrected right ascension (see Right As- 
 cension), subtracting it if the moon is east of the meridian, but 
 adding it if the moon is west of the meridian — the difference or 
 sum will be the right ascension of the meridian, from which (in- 
 creased by twenty-four hours if necessary for the purposes of 
 subtraction) subtract the sun's corrected right ascension, and 
 the remainder will be the astronomical apparent time at ship. 
 To this apply the corrected equation of time (see Equation of 
 
THE NAVIGATOR'S POCKET-BOOK 97 
 
 Time) according to heading of the almanac column and the 
 answer will be the astronomical mean time at ship ; then 
 the difference between this and the astronomical mean time 
 at Greenwich will be the longitude in time, which turned 
 into degrees (either by the use of Table 7 or by the rule given 
 under the head of Arithmetic of Navigation) will be the lon- 
 gitude. 
 
 Remarks. — When the astronomical mean time at the ship and 
 the astronomical mean time at Greenwich are of different dates, 
 it will be necessary to add twenty-four hours to the time of the 
 latest date for the purposes of subtraction between them, then 
 the answer will be the longitude in time. 
 
 As explained for the sun, the best hour to observe a time 
 altitude of a heavenly body is when it is the nearest to the prime 
 vertical. (See Prime Vertical.) 
 
 If desired, several altitudes of the moon may be observed in 
 quick succession and the corresponding times by the chronom- 
 eter noted, then the mean of these altitudes and times accepted 
 as a base from which to calculate the longitude. As explained 
 for the sun, this will eliminate any small error as regards the 
 altitude and noting of the time. 
 
 If the log. sine of the time cannot be matched, correct the time 
 given in the p.m. column according to the rule given under the 
 head of Logarithms. 
 
 Longitude by One Altitude of a Planet. — This problem is to 
 be worked in the same way as the one described immediately 
 preceding for the moon, simply substituting the planet's polar 
 distance and right ascension, as may be seen by the following 
 rule : 
 
 Add together the planet's corrected altitude, the latitude by 
 dead-reckoning, and the planet's polar distance ; divide by 2 
 7 
 
98 the navigator's pocket-book 
 
 and from the half-sum subtract the corrected altitude ; select 
 from Table 44 the logs, secant of latitude, cosecant of polar dis- 
 tance, cosine of half-sum, and sine of remainder ; add these four 
 logs, and divide by 2, calling the answer the sine of a time, 
 which take out in the p.m. column, Table 44, and apply said 
 time to the planet's corrected right ascension, subtracting it if 
 the planet is east of the meridian, but adding it if the planet is 
 west of the meridian— the difference, or sum, will be the right 
 ascension of the meridian, from which (increased by twenty- 
 four hours if necessary for the purposes of subtraction) subtract 
 the sun's corrected right ascension and the answer will be the 
 astronomical apparent time at the ship, to which apply the cor- 
 rected equation of time, then find the difference between this 
 astronomical mean time at ship and the astronomical mean time 
 at Greenwich ; the answer will be the longitude in time, which 
 convert into degrees. 
 
 Longitude by One Altitude of a Star. — As explained for a 
 planet, this problem is worked in the same manner as the moon, 
 it simply being necessary to substitute the star's polar distance 
 and right ascension ; but it is to be explained that corrections 
 for the declination and right ascension of stars are too small to 
 be considered, simply accepting the same for the given year 
 being all that is necessary. (See Fixed Stars.) 
 
 Longitude by Dead-Reckoning. —(See Dead-Reckoning.) 
 Longitude by the Artificial Horizon. — (See Artificial Hori- 
 zon.) 
 
 LONGITUDE IN ARC— The position or distance of a 
 vessel east or west of a given prime meridian, expressed in 
 degrees, minutes, and seconds of angular measure. 
 
 LONGITUDE IN TIME.— The position or distance of a 
 
THE NAVIGATOK'S POCKET-BOOK 99 
 
 vessel east or west of a given prime meridian, expressed in hours, 
 minutes, and seconds of time measure. 
 
 LOST DAY.— (See Circumnavigator's Day.) 
 
 LOWER LIMB.— (See Upper Limb.) 
 
 LOWER TRANSIT.— The passage of a heavenly body over 
 the meridian 180° distant from the meridian of the upper transit. 
 In high northern and southern latitudes at certain times of the 
 year the sun and moon do not set during the twenty-four hours, 
 but circle around the heavens, at all times in view of the ob- 
 server ; consequently they are then seen at the period of their 
 lower as well as upper transit. The Xautical Almanac gives the 
 astronomical times of the upper transit of heavenly bodies, which 
 takes place when the bodies are moving (apparently) from east to 
 west. (See Upper Transit ; Midnight Sun.) 
 
 LOW LATITUDES.— Parallels in the vicinity of the equa- 
 tor. (See High Latitudes.) 
 
 L'S OF NAVIGATION.— Lead, Lights, Lookout, Latitude, 
 Longitude. 
 
 LUBBER'S POINT.— The vertical black line painted on 
 the inside surface of the compass bowl, and which represents 
 the ship's head and the line of the keel. 
 
 LUNAR. — Relating to the moon. 
 
 LUNAR DAY. — The interval of time between two successive 
 transits of the moon over the same meridian. 
 
 LUNAR DISTANCE.— The angular measurement of the 
 moon from another heavenly body. 
 
 LUNAR INEQUALITY.— A variation in the moon's mo- 
 tion which depends upon its distance from the sun. 
 
100 THE NAVIGATOR'S POCKET-BOOK 
 
 MAGNET.— An ore that attracts iron. The properties of a 
 magnet are that, with the exception of the oxides, it attracts 
 iron in all of its various states. If a bar of steel is charged with 
 magnetism, either by a magnet or by a dynamo, then suspended, 
 horizontally balanced by a slender thread, the bar will indicate 
 the magnetic meridian. What is known as an artificial magnet 
 is a bar or mass of iron or steel into which the magnetic prop- 
 erty has been introduced by the presence of, or contact with, a 
 body possessing the same. 
 
 MAGNETIC. — Having power to attract iron. 
 
 MAGNETIC AMPLITUDE.— The bearing by compass of 
 a heavenly body at rising and setting, or an arc of the horizon 
 intercepted between the body in its rising and setting and the 
 east and west compass points. 
 
 MAGNETIC AZIMUTH— The arc of the horizon inter- 
 cepted between the vertical circle and the magnetic meridian, 
 or the bearing by compass of a heavenly body, calculated from 
 the north point in north latitudes and the south point in the 
 southern hemisphere. 
 
 MAGNETIC BEARING.— A bearing according to the 
 compass, or the direction pointed out by the magnetic needle. 
 
 MAGNETIC DIP. — A property belonging to the magnetic 
 needle, whereby one of its poles (ends) inclines toward the 
 earth, while the other pole is repelled or elevated. 
 
 MAGNETIC EQUATOR.— A line passing through those 
 points on the surface of the earth where the dipping needle rests 
 in a horizontal position. (See Compass.) 
 
 MAGNETIC INDUCTION.— Communication of magnetism 
 from a magnet to a body of steel in its vicinity, although per- 
 
THE NAVIGATOR'S POCKET-BOOK 101 
 
 haps not touching it. The communication of magnetism from 
 the earth (which is a huge magnet in itself) to the hulls of iron 
 and steel vessels is known as the earth's induction. 
 
 MAGNETIC MERIDIAN.— A vertical circle in the heav- 
 ens which intersects the horizon in the magnetic poles ; or it may- 
 he defined as the natural direction pointed out by the compass 
 needle when allowed to turn freely and removed from the effects 
 of deviation and local attraction. 
 
 MAGNETIC NEEDLE.— The slender piece of magnetized 
 steel to which the compass card is fastened. 
 
 MAGNETIC POLES — Two places on the earth's surface 
 where the dipping needle assumes apposition perpendicular to 
 the horizon and shows a dip of 90°. The north magnetic pole is 
 situated on the parallel of 70° north and on the meridian of 97° 
 west ; the south magnetic pole on the parallel of 70° south and 
 on the meridian of 145° east. 
 
 MAGNITUDE. — According to their brilliancy the stars are 
 classed as of the first, second, third, fourth, fifth, sixth, and 
 seventh magnitudes. Stars beyond the seventh magnitude can- 
 not be seen with the unaided eye, and are known as telescopic 
 stars. 
 
 MAKING THE LAND.— A landfall ; to obtain the first 
 view of land. 
 
 MAST-HEAD ANGLES.— To measure the distance between 
 the observer's ship and another vessel, it is only necessary to 
 know the height of her mast or smoke-stack, and the vertical 
 angle of the same measured to the surface of the water — to her 
 water-line. If the image of the truck, or the rim of the smoke 
 funnel is thrown to the water-line by the sextant, and this angle 
 
102 THE NAVIGATOR'S POCKET-BOOK 
 
 referred to the danger-angle tables in the back of this book, the 
 distance of the vessel will at once be obtained by simple inspec- 
 tion. 
 
 To tell, when in a race, if the distance between two vessels is 
 increasing or decreasing, note several mast-head angles. If the 
 angles increase it proves that the two vessels are drawing nearer, 
 but if the angles decrease the vessels are separating more and 
 more. (See Danger- Angle Tables.) 
 
 MAST-HEAD COMPASS.— A compass hung at the lower- 
 mast-head so as to remove it out of the influence of the magnet- 
 ism in the ship's iron. (See Elevator Compass.) 
 
 MEAN NOON. — The time that the mean sun is supposed to 
 cross the observer's meridian. 
 
 MEAN SOLAR TIME — Time calculated by the motion of 
 the mean sun. All watches and clocks represent mean solar 
 time. 
 
 MEAN SUN. — An imaginary sun which is supposed to 
 move uniformly and to cross the same meridian the same time 
 every day, thus giving a value of exactly twenty-four hours to 
 the day. This mean or fictitious sun sometimes crosses the 
 observer's meridian a little in advance of the true sun, and at 
 other times a little after it, and this difference or interval between 
 the real and imaginary suns is known as the equation of time. 
 
 By referring to the almanac it will be seen that four times in 
 each year the real and imaginary suns pass the same meridian at 
 the same time ; namely, about April 14th, June 13th, August 
 31st, and December 23d ; consequently on these days the equa- 
 tion of time may be considered as zero. The maximum equa- 
 tion of time is about 16 m. 20 sec. 
 
THE NAVIGATOR'S POCKET-BOOK 103 
 
 MEAN TIMS. — Same as mean solar time. 
 MERCATOR'S CHART.— (See Chart.) 
 
 MERCATOR'S SAILING.— A method of finding (indepen- 
 dent of the parallel rules and dividers) the true course and dis- 
 tance between two places by employing meridional parts instead 
 of the middle latitude. 
 
 Rule. — Find the difference of latitude and the difference of 
 longitude between the two places. If the two latitudes have 
 the same name (both north or both south) subtract one from 
 the other, but if they have different names add them together. 
 Now multiply the degrees of the answer by 60 to convert them 
 into miles and add in the minutes as they represent miles ; the 
 answer will be the difference of latitude. Proceed to find the 
 difference of longitude in the same way — add the longitudes to- 
 gether if of different names, but subtract between them if of the 
 same name. 
 
 Turn to Table 3 and select the meridional parts for the degrees 
 and minutes of each latitude, and if the latitudes are of differ- 
 ent names, add the meridional parts, but if the latitudes are of 
 the same name, subtract one of the meridional parts from the 
 other. In other words, if the latitudes were added the me- 
 ridional parts must be added, and if the latitudes were subtract- 
 ed the meridional parts must be subtracted. 
 
 With the meridional difference of latitude and the difference 
 of longitude turn to Table 2 and make them compare by seeking 
 in the latitude column for the meridional difference of latitude 
 and in the departure column opposite for the difference of longi- 
 tude. On the page of their comparison the true or geographical 
 course between the two places will be read in degrees from the 
 top of the page if the meridional difference of latitude is greater 
 
104 THE NAVIGATOR'S POCKET-BOOK 
 
 than the difference of longitude, but it will be read from the 
 bottom of the page if the difference of longitude exceeds the 
 meridional difference of latitude. 
 
 On the same page apply the proper difference of latitude in 
 the latitude column from that part of the page (top or bottom) 
 where the course was read, and opposite to the left in the dis- 
 tance column will be found the distance in nautical miles for 
 the course found, which, in other words, will be the number of 
 miles required to be sailed on a direct line between the ship's 
 place and the point sought. 
 
 The variation (also the deviation, if any exists) of the compass 
 must be applied to the true course in order to convert the same 
 into a magnetic course, or the course necessary to be steered by 
 the ship's compass in order to make the true track. 
 
 To Apply Variation. — Suppose the true course found is 
 southeast, and the chart informs us that in the ship's locality 
 there is one point of westerly variation. The effect of this is 
 that the southeast point of the compass is swung so that it really 
 points southeast -by-east, and in order to make a true southeast 
 course the ship must be steered southeast-by- south according 
 to the compass. 
 
 Rule. — A simple rule to remember for converting a true 
 course into a magnetic course is to allow westerly variation 
 away from the true course in the direction that the hands of a 
 watch revolve, and easterly variation contrary, or against the 
 hands of a watch. 
 
 To Apply Deviation. — If deviation exists for the magnetic 
 course found, the latter must have the deviation applied to it on 
 exactly the same principle as explained for variation. For ex- 
 ample, we will say that the magnetic course found is southeast- 
 by-south, and that there is one point of westerly deviation to be 
 
THE NAVIGATOR'S POCKET-BOOK 105 
 
 allowed for when the ship's head is on that course. The com- 
 pass course to be steered in this case is south-southeast, in order 
 to make a correct magnetic course of southeast-by-south. 
 
 Remarks. — The variation must always be applied before 
 applying the deviation. 
 
 It is to be remembered that the compass course must be re- 
 shaped as often as the variation changes. For example, we will 
 say that the true course from Sandy Hook to Bermuda Island is 
 S. 42° E., and that in the vicinity of Sandy Hook the variation 
 of the compass is 8° westerly. The magnetic course in this case 
 is S. 34° E., which equals southeast-by-south. To this course 
 we apply the deviation correction (if any exists) given by our 
 deviation card or found by observation, and then we hold the 
 indicated compass course until we reach a latitude and longitude 
 where the variation of the compass is shown to change, when it 
 becomes necessary for us to apply the new variation given by 
 the chart and change the course accordingly. 
 
 When, by reason of opposing winds or other causes, the vessel 
 does not keep on the direct course for the port bound to, then 
 the whole process of laying out the course must be gone through 
 with again. This may happen many times before the port is 
 reached. 
 
 Mercator's Sailing is to be preferred to Middle Latitude Sail- 
 ing, unless the course is nearly east or west. 
 
 MERCURIAL BAROMETER. — An instrument which 
 shows the pressure of the air or weight of the atmosphere. It 
 is a tube thirty-four inches long, closed at the top and exhausted 
 of air. The lower end of this tube is immersed in a cup or 
 cistern of mercury, and the pressure of the atmosphere causes 
 the fluid to ascend in the slender, hollow column. The varia- 
 tion in height of the mercury is dependent upon the weight or 
 
106 THE NAVIGATOR'S POCKET-BOOK 
 
 pressure of the atmosphere. These variations are measured by- 
 aid of a scale graduated in inches and parts and fixed against 
 the tube. When the mercury in the cistern is pressed down 
 by the air the mercury rises in the exhausted tube, but when 
 the mercury in the cistern rises on account of diminished press- 
 ure of air the mercury in the tube falls. (See Barometer.) 
 
 MERIDIAN. — The highest point of the great arc described 
 by a heavenly body from its rising to its setting. When the 
 sun crosses the observer's meridian it is 12 o'clock, apparent 
 noon, at his place. A meridian is an imaginary great circle of 
 the sphere extending from pole to pole. (See Circumnavi- 
 gator's Day ; Prime Meridian ; Secondary Meridians ; Tertiary 
 Meridians. ) 
 
 MERIDIAN ALTITUDE.— The angular height of a heav- 
 enly body from the horizon line at the time the body is crossing 
 the meridian. (See Altitude ; Latitude.) 
 
 MERIDIAN PASSAGE.— The crossing of a heavenly body 
 over the meridian of the observer. (See Lower Transit ; Upper 
 Transit.) 
 
 MERIDIAN SAILING.— Sailing on a meridian ; sailing 
 true north or south. (See Parallel Sailing.) 
 
 MERIDIONAL DIFFERENCE.— The quantity given in 
 Table 3, which bears the same proportion to the difference of 
 latitude that the difference of longitude bears to the departure. 
 
 MERIDIONAL FARTS.— Degrees of latitude increased 
 from their natural lengths more and more as the equator is 
 receded from, and the lengths of the small portions of the 
 meridian thus increased, expressed in minutes of the equator, 
 are called meridional parts. (Table 3.) 
 
THE HAVIGATOR's POCKET-BOOK 107 
 
 METEOROLOGY.— The science of the atmosphere and its 
 phenomena. (See Log-Book ; Weather.) 
 
 MIDDLE LATITUDE.— Half of the sum of two latitudes 
 of the same name, but half of the figures left after subtracting 
 between two latitudes of different names. The middle latitude 
 between 20° north and 30° north is 25° north. The middle lati- 
 tude between 20° north and 30° south is 5° south. 
 
 MIDDLE-LATITUDE SAILING— The method of finding 
 (independent of the parallel rules and dividers) the true course 
 and the distance between two places by employing the middle 
 parallel between them. 
 
 Rule. — Find the difference of latitude and the difference of 
 longitude between the two places. If the two latitudes have 
 the same name (both north or both south) subtract one from the 
 other ; but if they have different names add them together. 
 Now multiply the degrees of the answer by 60 to convert them 
 into miles, and add in the minutes as they represent miles ; the 
 answer will be the difference of latitude. Proceed to find the 
 difference of longitude in the same way : add the longitudes to- 
 gether if of different names, but subtract between them if of the 
 same name. 
 
 Next, to find the middle latitude : if the two latitudes are of 
 the same name add them together and divide by 2 ; but if they are 
 of different names subtract one from the other and divide by 2. 
 The answer will be the parallel equidistant between the place 
 of the ship and the port sought. 
 
 With this middle latitude turn to Table 2, and on the page 
 marked with the degrees of the middle latitude apply the dif- 
 ference of longitude in the distance column, and opposite to the 
 right in the latitude column (reading from the top of the page if 
 
108 THE NAVIGATOR'S POCKET-BOOK 
 
 the degrees were found there, but from the bottom of the page 
 if the degrees were found there) will stand the departure, or the 
 number of nautical miles in an east and west line between the 
 ship and the sought-for port. 
 
 K"ow, with the difference of latitude and the departure make 
 them compare in Table 2 in their respective columns opposite 
 one another, and in the distance column to the left will be seen 
 the direct distance to be sailed in nautical miles, and the true or 
 geographical course between the two places will be read in de- 
 grees from the top of the same page if the difference of lati- 
 tude is greater than the departure, but the course will be read 
 from the bottom of the same page if the departure exceeds the 
 difference of latitude. 
 
 The variation (also the deviation, if any exists) of the compass 
 must be applied to the true course in order to convert the same 
 into a magnetic course, or the course necessary to be steered by 
 the ship's compass, in order to make the true track. 
 
 To Apply Variation. — Suppose the true course found is 
 south and the chart informs us that in the ship's locality there 
 is one point of easterly variation. The effect of this is that the 
 compass south point is swung so that it really points south-by 
 west, and in order to make a true south course we must steer 
 south-by-east by the compass. 
 
 Rule. — A simple rule to remember for converting a true course 
 into a magnetic course is to allow the amount of westerly varia- 
 tion away from the true course in the direction that the hands 
 of a watch revolve, and easterly variation contrary or against 
 the hands of a watch. 
 
 To Apply Deviation. — If deviation exists for the magnetic 
 course found, the latter must have the deviation applied to it on 
 exactly the same principle as explained for variation. For ex- 
 
THE KAVIGATOK^S POCKET-BOOK 109 
 
 ample, we will say that the magnetic course found is northeast, 
 and that there is half a point of westerly deviation to be allowed 
 for when the ship's head is on that course. The compass course 
 to be steered in this case is northeast-half-east, in order to make 
 a correct magnetic course of northeast. 
 
 Remarks. — The variation must always be applied before ap- 
 plying the deviation. 
 
 It must be borne in mind that the compass course is to be re- 
 shaped as often as the variation changes. For example, we 
 will say that the true course found is N. 45° E., and that in the 
 locality of the ship the variation of the compass is 6° easterly. 
 The magnetic course in this case is N. 39° E., which equals 
 northeast half-north. To this course we apply the deviation 
 correction (if any exists) given by our deviation card or found 
 by observation, and then we hold the indicated compass course 
 until we reach a latitude and longitude where the variation of 
 the compass is shown to change, when it becomes necessary 
 to apply the new variation given by the chart, and change the 
 course accordingly. 
 
 When by reason of head winds or other causes the vessel 
 does not keep on the direct course for the port to which she is 
 bound, then the whole process of laying out the course must be 
 gone through with again. This may occur many times before 
 the port is reached. 
 
 Middle-Latitude Sailing is to be preferred to Mercator's Sail- 
 ing when the course is nearly east or west. 
 
 MIDDLE POINT.— (See Drift.) 
 
 MIDNIGHT SUN.— As explained under the head of Lower 
 Transit, in high latitudes during the summer season there are 
 times when the sun does not set for the observer during the 
 
110 THE NAVIGATOR'S POCKET-BOOK 
 
 twenty-four hours, and on account of crossing at 12 o'clock at 
 night the meridian 180° distant from the meridian which it 
 crossed when it made its upper transit, it derives its name of 
 the midnight sun. 
 
 MILE. — A statute mile is 5,280 feet ; a nautical or geograph- 
 ical mile 6,082.66 feet ; the latter is also called a knot. 
 
 MINUTE. — A mile of latitude and a minute of latitude are 
 of equal value — 6,082.66 feet. A minute of longitude varies 
 in value according to the distance from the equator. At the 
 equator a minute of longitude is equal to a minute of latitude. 
 On the parallel of 60° north or south a minute of longitude is 
 equal to only half a minute of latitude. Longitude value de- 
 creases in proceeding from the equator toward the poles, where 
 it is lost, all the meridians converging to a point ; consequently 
 neither the north nor south poles possess longitude. 
 
 MINUTE OF ARC. — A minute of angular measure ; a 
 minute measured on the sextant. 
 
 MIRROR. - (See Sextant.) 
 
 MIXED TRACE.— (See Great-Circle Sailing.) 
 
 MOON. — An opaque celestial body receiving its light from 
 the sun ; mean distance from the earth 238,800 miles ; diameter 
 2,160 miles ; mean apparent diameter 32'. 
 
 MOON CULMINATING STAR.— A star that crosses the 
 meridian at the same time that the moon makes its transit. 
 
 MORNING STAR. — When a planet rises before the sun it 
 is called the morning star, and when it appears in the western 
 sky shortly after sunset it is called the evening star. 
 
 NADIR. — The point of the heavens vertically under the ob- 
 server's feet. The nadir is diametrically opposite to the zenith. 
 
THE NAVIGATOR'S POCKET-BOOK 111 
 
 NATIONAL OBSERVATORY.— An astronomical estab- 
 lishment situated in the capital city of a nation. The meridian 
 which passes through the observatory is accepted as the first or 
 prime meridian of that country. (See Prime Meridian.) 
 
 NAUTICAL ALMANAC— (See Almanac.) 
 
 NAUTICAL ASTRONOMY. — That part of astronomy 
 which is used for determining the latitude and longitude of the 
 ship by calculations of the sun, moon, and stars. Amplitudes 
 and azimuths also belong to nautical astronomy. 
 
 NAUTICAL DAY.— Same as sea day. 
 
 NAUTICAL MILE.— (See Mile.) 
 
 NAUTICAL STARS.— Certain bright stars tabulated in the 
 Nautical Almanac, used by navigators for determining the ves- 
 sel's position. The principal ones are given in the star tables in 
 the back of this volume, and under the head of Fixed Stars. 
 (See Latitude.) 
 
 NAUTICAL TABLES.— Specially computed tables for the 
 solution of navigation problems. Bowditch's tables, published 
 by the United States Government, are accepted by the naval au- 
 thorities of all nations as standard, although England, France, 
 and other countries have their own tables. Bowditch's tables 
 are the ones referred to throughout the text of this work. 
 
 NAVIGATING COMPASS.— The standard compass. 
 
 NAVIGATION. — The science of locating the position of a 
 ship at sea, and conducting a vessel from one port to another. 
 
 NEUTRAL POINT. — A magnet in the shape of a steel bar 
 has a north polarity at one end and a south polarity at the other. 
 The middle of the bar is totally devoid of magnetism, and this 
 space is called the neutral point. 
 
112 THE NAVIGATORS POCKET-BOOK 
 
 NOCTURNAL.— Relating to the night. 
 
 NOCTURNAL ARC— The fire described by a heavenly 
 body from its setting to its rising. 
 
 NODE. — When a planet crosses from north to south it is in 
 the descending node, and when it crosses from south to north it 
 is in the ascending node. 
 
 NOON. — When the centre of the real sun is on the observer's 
 meridian it is apparent noon not only with him but at all places 
 on his meridian from pole to pole. (See Mean Sun ; Siderial 
 Noon.) 
 
 OBJECT-GLASS.— The lens situated in the large end of a 
 telescope, the same being the first to receive the image or rays 
 of light. 
 
 OBSERVATION.— To determine the angular height of a 
 heavenly body above the horizon for the purpose of calculating 
 the ship's position. 
 
 OCCULTATION.— The eclipse of one heavenly body by 
 another. 
 
 OCTANT. — A nautical instrument of reflection for measuring 
 altitudes of heavenly bodies. It is constructed on the same 
 principles as the sextant, but of more limited arc and graduated 
 to only 15" instead of 10". The metal-frame and silver-arc oc- 
 tant with an arc reading to about 120° is a much superior instru- 
 ment in every way to the quadrant. The manner of adjusting 
 and using the octant is identical with that of the sextant, conse- 
 quently it would be repetition to treat the subject under this 
 head, and the reader is referred to the rules given under the 
 head of Sextant. Some old-fashioned octants are cut to 20" of 
 arc and others even to 30". (See Quadrant ; Sextant.) 
 
THE NAVIGATOR'S POCKET-BOOK 113 
 
 OFF THE ARC— (See Sextant.) 
 
 OIL COMPASS. — A liquid compass ; a compass in which 
 the card floats about in oil instead of a mixture of alcohol and 
 water. (See Liquid Compass.) 
 
 ON THE ARC— (See Sextant.) 
 
 OPPOSITION.— When a heavenly body is 180° of longitude 
 distant from the sun it is said to be in opposition. 
 
 ORBIT.— The imaginary path described by a heavenly body 
 in its revolution ; the track of a planet round the sun. 
 
 P.M. — Post Meridiem ; after meridian ; embraces the twelve 
 hours from noon to midnight. 
 
 PARALLAX. — The apparent displacement of a heavenly 
 body as seen from two different stations. The sun's parallax is 
 shown in Table 16 ; the moon's parallax (less refraction) in Table 
 23, and the parallax of the planets in Table 17. (See Corrected 
 Altitude ; Horizontal Parallax.) 
 
 PARALLEL RULES.— Two flat rules connected with piv- 
 oted cross-hinges so that the rules may remain parallel when 
 spread out. They are used for shaping courses and determining 
 bearings on the chart. 
 
 PARALLELS.— Circles of latitude parallel to the equator. 
 
 PARALLEL SAILING.— Sailing on a parallel ; sailing true 
 east and west. (See Meridian Sailing.) 
 
 PARHELIA. — A mock sun ; an image of the sun which is 
 occasionally seen close to and at the same height above the hori- 
 zon as the true sun. 
 
 PASSAGE.— (See Meridian Passage.) 
 
 PATENT LOG. — An instrument for measuring the distance 
 8 
 
114 THE NAVIGATOR'S POCKET-BOOK 
 
 (in nautical miles) run by a vessel. It consists of a register, 
 rotator, and line, the latter connecting the two metal parts. The 
 rotator is towed astern, and by its revolutions turns the line com- 
 municating with the register and turns the dial hands within. 
 
 To Rig the Log. — Pass the log-line through the long fore-and- 
 aft hole in the rotator and make a small Flemish eye in the end of 
 the line ; then sew a piece of leather for chafing gear around that 
 part of the line which rubs against the small or forward end of 
 the rotator. Next secure the Flemish eye to the after-part of the 
 rotator by the wooden or metal peg furnished, and fasten the 
 hook to the other end of the line by a couple of half-hitches. 
 Secure the indicator so that it will ride freely on the tafTrail, 
 permitting the angle of the indicator bar to correspond with the 
 angle of the line, thus preventing undue friction upon the shaft- 
 bearing when the log is being towed. Give line to the rotator 
 according to the freeboard and speed of the vessel. A very high 
 freeboard, or a steamer making more than ten knots, will require 
 all the line furnished to prevent the rotator from skipping, 
 whereas a low freeboard or a vessel making anywhere from five 
 to ten knots will require about two-thirds of the line. 
 
 To Read the Dial. — Some registers have two and some three 
 dials. In the latter case the first one is marked in quarters, each 
 division representing one-quarter of a mile ; the second in even 
 miles, recording as high as ten ; the third in ten-mile divisions, re- 
 cording as high as one hundred. When the ship has sailed one 
 hundred miles, the three hands all point at zero, and at such 
 time a suitable memorandum is made in the log-book, so that 
 the record may be faithfully preserved. Where the register has 
 onl} T two dials, one of them represents quarter miles and the 
 other single-mile divisions extending to one hundred. 
 
 Remarks. — When a vessel's speed exeeeds eighteen miles an 
 
THE NAVIGATOR'S POCKET-BOOK 115 
 
 hour, the majority of patent logs are of little value, as they will 
 not record correctly the distance run by the vessel on account of 
 skipping. If sufficient line is given them to overcome this skip- 
 ping and attendant loss, they will be too sluggish to render an 
 honest return. In such cases recourse is had to the chip log, 
 and the rough distance run is also calculated by dividing the 
 number of revolutions made by the propeller by the number 
 allowed for one mile. 
 
 To Allow for Current. — When a ship is sailing with or against 
 a current, the velocity of same must be taken into account and 
 applied either as a plus or minus quantity to the reading of the 
 dial. 
 
 Examples. — According to the register, the vessel heading west 
 has made ten miles in the past hour, but it is known that during 
 that time the ship has been in a current flowing west at the rate 
 of two miles an hour ; consequently this two miles must be added 
 to the reading of the register, making the corrected distance run 
 twelve miles. 
 
 The register shows that during the past hour the vessel head- 
 ing south has made ten miles, but it is known that during 
 that time the ship has been in a current setting north at 
 the rate of two miles an hour ; consequently this two miles must 
 be subtracted from the reading of the register, making the cor- 
 rected distance run only eight miles. 
 
 Explanation. — When a vessel is going neither directly with 
 or against a current, but sailing a course that makes an angle 
 with it, then it becomes a calculation of current sailing, and 
 must be considered in the manner explained under that head. 
 
 PATTERSON'S METHOD.— (See Chart Sailing.) 
 
 PELORUS. — An instrument much used for observing bear- 
 
116 THE NAVIGATOR'S POCKET-BOOK 
 
 ings and for finding the deviation of the compass, taking the 
 place of the azimuth attachment, shadow-pin, etc. It consists of 
 a circular dial of brass graduated with the points and degrees of 
 the compass, and two upright arms which revolve around the 
 circle. This plate is hung in gimbals so that it will preserve a 
 horizontal position when the vessel pitches and rolls. One of the 
 uprights is fitted with a perpendicular thread running its length, 
 also a small hinged mirror at its base, and the other upright is 
 provided with a colored eye-screen which is made to slide up 
 and down the length of the arm, and is for the purpose of pro- 
 tecting the eye from the glare of the sun when taking a bearing 
 of that body. A mark on the inner gimbal ring indicates the 
 line of the keel or the ship's head, and a clamp screw admits of 
 the dial being secured against turning after it has been set. 
 
 Pelorus Stands. — Suitable stands for the pelorus should be 
 provided on different parts of the deck, in order that bearings 
 may be taken at any station by simply carrying the pelorus to it 
 and setting it on its stand. The idea of this is that if the view is 
 obstructed (by a mast, funnel, sail, or deck-house) from one 
 point, another may be selected which will give a clear field. It 
 is recommended that steamships have stands built on each end 
 of the bridge and on each quarter. These stands require to be 
 but simple shelves hinged to the rail and provided with raised 
 strips or coamings of wood running round them for the pelorus 
 box to snugly set into and to protect the same from rolling off. 
 The stands must have their fore-and-aft coamings parallel to the 
 ship's keel, so that when the pelorus box is placed, the zero line 
 of the card will coincide with the line of the keel. The man- 
 ner of effecting this is explained in the following : 
 
 The ship being on an even keel while in dock or at anchor in 
 the stream, set the pelorus square on one of the shelves, with the 
 
THE NAVIGATOR'S POCKET-BOOK 117 
 
 lubber's mark forward, and measure carefully the distance from 
 the centre of the instrument to the midship seam of the deck, 
 then lay off toward the bulwarks from this seam a conspicuous 
 mark on the forward deck (on the side that the instrument is on) 
 the same distance as exists between the pelorus and the seam. 
 Next set the zero point of the pelorus dial to the lubber's mark 
 on the gimbal ring, and observe that the sight-vanes are placed at 
 zero. Look forward through the sight-vanes at the mark erected, 
 and move the box one way or the other until the mark is seen 
 to be cut by the thread. Now secure the coamings on the lines 
 indicated by the box, and proceed in a like manner for each one 
 of the shelves. 
 
 To Take a Bearing. — Set the pelorus to the course of the 
 ship according to the standard or navigating compass, then so 
 long as the ship is held steady on said course, any bearings taken 
 by the pelorus will represent the magnetic bearing of the object 
 exactly the same as though it had been observed directly from 
 the standard compass itself. 
 
 In order to find the deviation of any particular compass, simply 
 set the pelorus to the course of the ship as shown by that com- 
 pass, and proceed to take the sun's bearing and work out the am- 
 plitude or azimuth. (See Amplitude ; Azimuth.) 
 
 PERMANENT MAGNETISM.— An artificial steel magnet 
 will part with a little of its original strength after being charged, 
 the balance contributing what is known as its saturation point, 
 which it will retain for many years without appreciable loss, 
 and is known as permanent magnetism. 
 
 PERPENDICULAR.— A line at right angles to the plane of 
 the horizon ; a plumb-line ; a line at a right angle to the base. 
 
 PERSONAL EQUATION.— The difference in judgment 
 
118 THE NAVIGATOR'S POCKET-BOOK 
 
 shown between two observers in measuring an altitude of the 
 same object, etc. 
 
 PLANE. — A level surface. In astronomy planes are ideal 
 and pass through certain points of the heavens — planes of the 
 horizon, equator, etc. 
 
 PLANE CHART. — A chart representing the earth's surface 
 as a plane. 
 
 PLANE SAILING, — Calculating courses, etc., on the sup- 
 position that the surface of the earth is a plane. 
 
 PLANET. — An opaque celestial bod}% which, like the moon, 
 receives its light from the sun. The nine principal planets are 
 Mercury, Venus, Earth, Moon, Mars, Jupiter, Saturn, Uranus, 
 Neptune. (See Fixed Stars.) 
 
 PLANISPHERE.— A chart of the heavens. 
 
 PLOTTING. — To plot the latitude and longitude of a vessel 
 is to trace on a chart the courses and distances made. Where 
 the last line ends will be the ship's place. It is a modification of 
 dead-reckoning. 
 
 POINT. — One of the thirty-two divisions of the compass card ; 
 exact place ; station. 
 
 POINTERS.— The two stars in the ladle of the Dipper that 
 point out the North Star. (See Dipper.) 
 
 POLAR CIRCLES.— The two parallels situated 23° 28' from 
 the poles of the earth. (See Antarctic Circle ; Arctic Circle.) 
 
 POLAR DISTANCE. — The angular distance of a heavenly 
 body from the elevated pole, the same being found by either 
 adding its declination to or subtracting it from 90°. Polar dis- 
 tance is reckoned from the pole that is in the hemisphere of the 
 observer. For example, if the observer is in north latitudes, the 
 
THE NAVIGATOR'S POCKET-BOOK 119 
 
 angular distance of the body would be figured from the ele- 
 vated north pole, and if the observer was in the southern hemi- 
 sphere, it would be measured from the south pole. 
 
 Examples. — An observer situated north of the equator wishes 
 to know the sun's polar distance. The declination of the body 
 is 10° north ; consequently the sun's north polar distance is 80°. 
 
 An observer situated south of the equator requires the moon's 
 polar distance. The declination of the body is 20° north ; con- 
 sequently the moon's south polar distance is 110°. 
 
 POLARIS.— The Pole or North Star. It is a star of the sec- 
 ond magnitude in the tail of the Little Bear. Polaris is only 
 about li° from the pole, and its altitude is always the approxi- 
 mate latitude of the observer. When Polaris is at its greatest 
 distance from the meridian its altitude is practically the same as 
 the elevation of the pole, which is equal to the latitude of the ob- 
 server. Polaris is calculated to be two hundred and ninety- two 
 millions of miles from the earth. Polaris is approaching the 
 pole, and in a hundred and twenty years from now it will be 
 about 30' from it, after which it will commence to recede. These 
 changes arise from the precession of the equinoxes. The annual 
 variation of the declination of Polaris is 19" ; in other words, 
 it is approaching the pole at the rate of 19" yearly. 
 
 POLE COMPASS. — A. compass that is elevated above the 
 deck by means of a long, stout pole. Access is had to the in- 
 strument by a ladder fixed permanently between the deck and 
 the top of the pole. The compass is so situated to remove it 
 beyond the disturbing influences of the ship's iron. 
 
 POLES. — The extremities of the earth's axis ; the two points 
 on the earth's surface 90° distant from the equator. (See Mag- 
 netic Poles.) 
 
120 THE XAVIGATOR'S POCKET-BOOK 
 
 POSITION.— Relating to the place of the ship. 
 
 PRECESSION OF THE EQUINOXES.— The equinoctial 
 points do not preserve a constant place among the stars, but 
 move backward, or toward the west, along the ecliptic at the 
 annual rate of 50"; consequently a complete revolution occu- 
 pies 25,868 years. The precession is caused by the unequal at- 
 traction of the sun and moon on the equator, combined with the 
 earth's rotation on its axis. 
 
 PRICKING POSITION.— With the dividers take from the 
 graduated meridian on the side of the chart the given latitude 
 and mark this on the meridian the nearest to the given longitude ; 
 then lay the bevelled edge of the parallel rules on a near parallel 
 and slide them along to the point marked on the meridian. Now 
 with the dividers take the given longitude from the graduated 
 parallel and lay this down along the edge of the parallel rules, 
 and this will define the ship's latitude and longitude. 
 
 PRIMARY MERIDIAN.— Same as Prime Meridian. 
 
 PRIME MERIDIAN.— The starting-point of longitude. 
 The first meridian of a country established by the situation of its 
 national observatory. Longitude is counted east and west from 
 the first meridian up to 180°. The French use the meridian of 
 Paris as a first meridian ; the English that of Greenwich ; the 
 Russians that of St. Petersburg ; the Americans that of Wash- 
 ington, etc. For convenience, American navigators (and others) 
 also use the meridian of Greenwich, as it permits them to navi- 
 gate by English charts, many of the same representing parts of 
 the world of which we have no survey of our own. For pur- 
 poses of navigation, a chronometer must be regulated to the 
 prime meridian of the country whose chart is used — if a French 
 chart is employed, the chronometer must be set to Paris time ; 
 
THE NAVIGATOR'S POCKET-BOOK 121 
 
 if an English chart is used, the chronometer must represent 
 Greenwich time, etc. (See Circumnavigator's Day ; Secondary 
 Meridians.) 
 
 PRIME VERTICAL. — The vertical circle passing through 
 the east and west points of the horizon. A heavenly body is in 
 or on the prime vertical when it hears true east or true west — 
 when it is at right angles to the meridian. When a body is ob- 
 served on the prime vertical for the purpose of calculating the 
 longitude, a considerable error in the latitude by dead-reckon- 
 ing (used in the computation) will not appreciably affect the re- 
 sult. By this it will be understood that the best time to observe 
 a longitude sight (be it sun, moon, planet, or star) is when the 
 body is on the prime vertical ; but it is to be explained that it 
 is not always possible to obtain such an observation, for a heav- 
 enly body can only bear true east or true west when its declina- 
 tion is of the same name as the ship's latitude and less than the 
 latter. When the declination of the body is of the same name 
 but greater than the ship's latitude, the body's nearest approach 
 to the prime vertical will be some time after it has risen ; but 
 when the declination is of a contrary name to the latitude, the 
 body will be the nearest to the prime vertical at its rising and 
 setting. By referring to a set of azimuth tables the navigator 
 will be able by mere inspection to determine the hour and min- 
 ute that the body will be on or will approach the nearest to the 
 prime vertical. All that is necessary is to refer to the page show- 
 ing the ship's latitude and the declination, then run down the 
 latter column until the closest figures to 90° are obtained, and 
 look opposite in the side column for the time. When the dec- 
 lination and the latitude are nearly the same, the sun will be 
 nearest the prime vertical a short time before and after its merid- 
 
122 
 
 ian passage, consequently at such times a very high altitude 
 may be employed for finding the longitude of the ship. 
 
 PRISMATIC ATTACHMENT.— A small portable instru- 
 ment fitted with a prism-glass, so adjusted on top of the com- 
 pass glass that the bearing of an object may be read from the 
 compass card by reflection. 
 
 PROJECTIONS.— Charts ; maps ; delineations. 
 
 PROTRACTOR. — An instrument for measuring angles. 
 (See Course Protractor.) 
 
 QUADRANT. — A navigating instrument of reflection used 
 for measuring angles. It is on the same principle as the octant 
 and sextant, but inferior in construction and graduated only to 
 1* of arc. 
 
 Description of the Quadrant. — The quadrant contains an arc 
 of 45°, but owing to its double reflection it measures 90°, read- 
 ing from right to left. The arc is divided into degrees, and 
 these are subdivided into three parts of twenty minutes each, 
 and the vernier on the sliding limb is divided into single min- 
 utes. The sliding or index limb is moved from right to left in 
 measuring altitudes, and the screw on the back is used for 
 clamping it against the arc after the altitude has been roughly 
 measured. The screw on the forward part of the limb is called 
 the tangent screw (set tangent to the arc) and is used for gently 
 moving the sliding limb when it is clamped so as to make a 
 perfect contact of the body with the horizon. The colored 
 glasses are for shading the e} T e when obtaining an altitude of 
 the sun. 
 
 To Read the Altitude. — Ascertain the number of degrees and 
 thirds of a degree that the zero on the vernier has passed on the 
 arc, then look along the vernier until one of its lines cuts ex- 
 
THE HAVIGATOH'S POCKET-BOOK 123 
 
 actly with one of the lines on the arc, and the number of min- 
 utes given on the vernier will be added to the reading originally 
 obtained on the arc — the whole answer being the required alti- 
 tude. 
 
 Remarks. — The quadrant is a crude instrument, and is not 
 used by good navigators. The metal-frame octant and the sex- 
 tant are standard instruments, but on account of the sextant 
 affording means of measuring greater angles than the former, it 
 is to be preferred to the octant. 
 
 The quadrant is adjusted in the same manner as explained for 
 the sextant. (See Octant; Sextant.) 
 
 QUADRANTAL DEVIATION.— The deviation of the com- 
 pass arising from the difference of the induced magnetism in 
 the thwartships and horizontal iron in the ship, and which is 
 corrected by two iron spheres attached to the port and star- 
 board sides of the binnacle. These spheres are known as quad- 
 ran tal correctors. 
 
 QUADRATURE.— When the moon is 90° from the sun— at 
 one of the two points in her orbit equally distant from the con- 
 junction and opposition — she is said to be in quadrature. 
 
 RADIUS. — The distance from the centre of a circle to its cir- 
 cumference. 
 
 RATE. — The daily variation of a chronometer from the time 
 of the meridian to which it is set. The aggregate of the gain or 
 loss is respectively subtracted from or added to the face of the 
 chronometer in order to obtain the correct Greenwich mean time 
 at the instant of observation. 
 
 Sea Rate.— Sometimes the chronometer does not maintain 
 when at sea the rate furnished for it by the makers or dealers, 
 and which is known as the instrument's shore rate. To as- 
 
124 
 
 certain the sea rate, take the difference between the chronom- 
 eter's error on the day of sailing and the gross error deter- 
 mined when the vessel makes port, and the result divided by 
 the number of days at sea will be the sea rate. (See Chronom- 
 eter.) 
 
 RATIONAL HORIZON.— A plane passing through the cen- 
 tre of the earth and parallel to the sensible horizon at the ob- 
 server's station. (See Sensible Horizon.) 
 
 READING. — To read an altitude is to observe the height of 
 an object recorded on the arc of a sextant, octant, etc. 
 
 RECIPROCAL BEARINGS.— Mutual bearings of the same 
 object by two compasses placed in line, one on board and the 
 other on shore where it is free from magnetic disturbances in 
 the way of local attraction. 
 
 REDUCTION. — To change hours, minutes, and seconds into 
 arc, or to change degrees into time. To apply a certain quan- 
 tity of arc to an ex-meridian altitude is called reduction to the 
 meridian. 
 
 REFRACTION.— The change of direction of a ray of light 
 in passing through atmospheric mediums of varying densit} T . 
 Refraction is ever a minus correction, and is tabulated in Table 
 20 for all heavenly bodies. It is to be explained, however, that 
 Table 23 gives the parallax of the moon, less the refraction. (See 
 Corrected Altitude.) 
 
 REGULATING. — What is known as regulating a watch or 
 clock at sea is simply to correct it so that it will show the local 
 apparent time at ship. It is done as follows : Observe an alti- 
 tude of the sun as for a regular chronometer sight for rinding 
 longitude, and also note the time shown by the ship's clock at 
 
THE NAVIGATOR'S POCKET-BOOK 125 
 
 the instant ; then proceed to work up the sight by the regular 
 rule (see Longitude), and compare the apparent time at ship 
 given for the sine of the logarithms with the time shown by the 
 clock when the sight was taken ; the difference will be the error 
 of the clock, the hands of which will be set back or advanced 
 as required. This method is also known as finding the time. 
 
 RESIDUAL ERRORS.— Deviation remaining after the com- 
 pass has been adjusted as closely as possible. (See Compass.) 
 
 RETENTIVE MAGNETISM.— When a ship's head has 
 been in one direction for a long time either at a dock or on a 
 long course at sea, the hull becomes temporarily magnetized in 
 a direction parallel to the magnetic meridian, owing to the 
 earth's inductive force. Sometimes this magnetism remains for 
 several days after the direction of the ship's head has been 
 changed, hence its name " retentive." It then gives way to 
 magnetism induced in a new direction according to the change 
 of course. It is because of this retentive magnetism that the 
 deviation card should be continually checked at sea, especially 
 upon changing the course. The temporary effect of retentive 
 magnetism upon the compass is to cause it to deviate invariably 
 in the direction of the last course, hence if a vessel has been 
 heading south for several days, and her course is changed to 
 west, it will be found that the natural deviation for that point 
 has been increased if the deviation has been westerly, and dimin- 
 ished if it has been easterly. 
 
 REVOLVING STORM.— (See Law of Storms.) 
 RHUMB LINE.— The track of a ship sailing constantly 
 toward the same point of the compass ; a line prolonged on a 
 nautical chart from any point of the diagram compass. 
 RIGHT ASCENSION.— The distance considered in time of 
 
126 THE NAVIGATOR'S POCKET-BOOK 
 
 a heavenly body reckoned eastward on the equinoctial from the 
 First Point of Aries— counted from h. to 24 h. (0° to 360°). 
 The First Point of Aries is that point in the heavens which the 
 sun's centre occupies at the time of the vernal equinox, when 
 the body changes from south to north declinations. Right as- 
 cension may be expressed as the celestial longitude of a heaven- 
 ly body. The correction for the hourly or minute difference of 
 right ascension is found and applied in the same wa}^ as explained 
 for the difference of declination. In other words, the right as- 
 cension is reduced to the Greenwich time of observation as 
 shown by the chronometer, by multiplying the hourly difference 
 in the case of the sun and planets, but the minute difference in 
 the case of the moon, and then adding this correction to or sub- 
 tracting it from the right ascension proper according as the lat- 
 ter is increasing or decreasing. 
 
 RIGHT ASCENSION OF THE MERIDIAN.— The angle 
 at the pole included between the meridian of the observer and 
 the meridian passing through the First Point of Aries. It is 
 reckoned eastward in the order of the signs. Sidereal time and 
 right ascension of the meridian are one and the same thing. In 
 other words, the hour angle of the First Point of Aries is equal 
 to the right ascension of the meridian of an observer, which is 
 precisely the same thing as sidereal time. 
 
 RIGOROUS METHOD.— Navigation problems calculated 
 according to exact principle ; allowing of no abatement ; accu- 
 rate in the smallest detail. 
 
 RISING.— The appearance of a heavenly body mounting 
 above the horizon. Celestial bodies continue to rise from the 
 eastern horizon line until they cross the meridian of the observ- 
 er, when they begin to fall. 
 
THE NAVIGATOR'S POCKET-BOOK 127 
 
 ROUGH LOG.— Same as log slate. 
 
 SAILINGS.— (See Great-Circle, Mercator's, Meridian, Mid- 
 dle-Latitude, Parallel, Plane, and Spherical Sailings.) 
 
 SATURATION POINT.— (See Permanent Magnetism.) 
 
 SEA DAY.— The old fashioned way of keeping the date at 
 sea was to consider the day and date to commence at noon and 
 to end and begin again the following noon, so that the sea clay 
 and date began twelve hours before the civil date and twenty- 
 four hours before the astronomical date. This ridiculous prac- 
 tice belongs entirely to the past. 
 
 SEA RATE.— (See Rate.) 
 
 SECONDARY MERIDIANS— Those connected with the 
 prime meridian by exchange of telegraphic time signals. Sec- 
 ondary meridians are determined with the utmost degree of care 
 in order to locate with accuracy the positions of prominent 
 points on the coasts. (See Tertiary Meridians.) 
 
 SEMICIRCULAR DEVIATION.— So called because it has 
 the contrary name and maximum value in opposite semicircles ; 
 for instance, if it is westerly on north it will be easterly on south. 
 
 SEMIDIAMETER.— Half a diameter. The semidiameters 
 of the sun and moon are given in the Nautical Almanac for every 
 day of the year, but for purposes of practical navigation these 
 may be called 16'. (See Corrected Altitude.) 
 
 SEND OF THE SEA — (See Heave of the Sea.) 
 
 SENSIBLE HORIZON.— A plane which is tangent to the 
 surface of the earth where the observer is situated. This plane 
 extends north, south, east, and west until bounded by the sky. 
 (See Visible Horizon.) 
 
 SET.— A heavenly body sets when its upper limb dips below 
 
128 THE navigator's pocket-book 
 
 the horizon line , an altitude is set when the sliding limb of the 
 sextant is clamped against the arc ; the space (span) contained 
 between the points of the dividers in measuring a distance on 
 the chart is known as a set ; to set the ship's course is to com- 
 mence steering in the calculated direction ; the set of a current 
 is the direction of its flow. 
 
 SEXTANT.— An instrument of reflection used by navigators 
 for measuring the altitudes of heavenly bodies, and for observ- 
 ing angles. It is of more delicate mechanism than the quadrant 
 or octant, and where the former is graduated (or cut, as it is 
 often called) to minutes, and the latter to 15" of arc, the sextant 
 reads to 10". The engraving in the front of the book represents 
 the navigator's sextant. 
 
 Names of Various Parts. — A, the graduated arc ; the divi- 
 sions of the arc are 10' each, and these are subdivided by the 
 vernier to 10" ; H, the handle, by which the sextant is held in 
 the right hand ; M, the mirror, or index-glass, at the end of the 
 sliding limb ; m, the horizon-glass ; E, the magnifying telescope, 
 for giving greater distinctness to the images, is placed in the 
 line of sight and supported in the ring or collar, K, which can 
 be moved by a screw at the back in a direction at right angles to 
 the plane of the sextant, so that the axis of the telescope may be 
 directed either toward the silvered or transparent part of the 
 horizon-glass ; the vernier is read by means of the magnifying- 
 glass, R, attached to a revolving arm, S, which is secured upon 
 the index bar or sliding limb ; P and Q, the colored shade- 
 glasses, for shielding the e} 7 e from the glare of the sun ; P, the 
 shades through which the image of the sun passes from the mir- 
 ror to the horizon-glass ; Q, the back shade-glasses for protect- 
 ing the eye from the glare of the horizon showing through the 
 unsilvered part of the horizon-glass ; B, the tangent screw (set 
 
THE KAVIGATOll's POCKET-BOOK 129 
 
 tangent to the plane of the instrument) by which the vernier may 
 be moved delicately along the arc after the sliding limb has been 
 clamped by the screw C at the back ; I, the inverting telescope ; 
 F, the simple tube without glasses for giving a direct line of 
 sight from the centre of the telescope ring to the horizon-glass. 
 
 The inverting telescope, with its parallel wires, is principally 
 used for measuring angular distances of heavenly bodies — a 
 branch of nautical astronomy that does not come within the 
 limits of this work. Altitudes may be measured by it in place 
 of either of the other telescopes, but it requires considerable 
 practice and a very steady hand. As its name implies, objects 
 viewed through it appear upside down, so that to measure an 
 altitude by it the navigator would bring the horizon down to the 
 sun, instead of the sun down to the horizon. 
 
 The small key shown is for adjusting the horizon-glass, and 
 the small ring beside it contains a colored glass, and this may be 
 screwed on the eye end of the telescopes as a substitute for the 
 shacle-glasses. 
 
 The star telescope contributes illuminating power to an obser- 
 vation owing to its short tube and large object-glass, and permits 
 the navigator to see the horizon distinctly when otherwise it 
 would be obscured. If not provided with this valuable adjunct 
 the navigator should have one fitted to his sextant, and be partic- 
 ular that its collimation adjustment is made perfect. 
 
 Adjustment of the Index-Glass. — This glass must be per- 
 pendicular to the plane of the sextant. To. prove this, set the 
 vernier to about the centre of the arc and clamp it, then look 
 obliquely into the index-glass and observe if the arc seen direct 
 and its reflection form one continuous line ; if so, the glass is 
 perpendicular to the plane of the instrument, but if the reflected 
 image appears to be lower than the other it proves that the glass 
 9 
 
130 THE NAYIGATOK'S POCKET-BOOK 
 
 leans backward ; if, however, the reflected image appears to be 
 higher than the other the glass leans forward. 
 
 Adjustment of the Horizon-Glass. — This glass must also be 
 perpendicular to the plane of the sextant. To test this, let zero 
 on the vernier cut zero on the arc, and hold the instrument al- 
 most horizontal, noting if the direct and reflected images of the 
 horizon line coincide — that is, if they show as an unbroken line 
 both in the silvered and clear parts of the glass. If they do, the 
 horizon-glass is perpendicular, but if they do not, then adjust 
 the glass to the required angle by the adjusting screw. 
 
 The Two Glasses to Be Parallel.— With the two zeros cut- 
 ting, hold the instrument vertically, and if the direct and 
 reflected images of the horizon line show as an unbroken and 
 continuous line the horizon-glass is parallel to the index-glass, 
 but if they do not show in an unbroken line adjust the horizon- 
 glass by its adjusting screw. 
 
 To Find the Index Error. — Should it prove impossible to 
 obtain a perfect adjustment find the error of the instrument as 
 follows : let the two zeros cut, then holding the instrument 
 vertically look at the horizon and gently finger the tangent 
 screw so as to move the vernier either forward or backward along 
 the arc until the image of and the horizon line itself show in an 
 unbroken line across the glass ; then the difference between zero 
 on the vernier and zero on the arc will be the index error, and 
 the amount of same will be added to any altitude observed by 
 the instrument if zero on the vernier is to the right hand (off the 
 arc) of zero on the arc, but the amount will be subtracted if 
 zero on the vernier is to the left hand (on the arc) of zero on 
 the arc. 
 
 Telescope Adjustment. — Screw T in the telescope containing 
 the two parallel wires and see that they are turned until parallel 
 
THE NAVIGATOR'S POCKET-BOOK 131 
 
 with the plane of the sextant ; then select two stars, at least 90° 
 apart, and make an exact contact at the wire nearest the plane 
 of the instrument, and read the measured angle. Move the 
 sextant so as to throw the objects on the other wire, and if the 
 contact is still perfect the axis of the telescope is in its right situ- 
 ation and the telescope adjustment is correct. If the images 
 have separated it shows that the object end of the telescope 
 droops toward the plane of the sextant, and if the images over- 
 lap it proves that the object end of the telescope points away 
 from the plane of the instrument. This will be rectified by the 
 screws in the collar of the sextant. A defect in the telescope 
 adjustment always makes angles too great. (See Axis of Col- 
 limation.) 
 
 Tormenting a Sextant. — The author desires to caution 
 navigators against tormenting a sextant continually. A good 
 instrument once placed in perfect adjustment (unless it meets 
 with a heavy jar or fall) will keep in adjustment for a long time, 
 and if let alone will give more satisfactory work than if the 
 threads of the adjusting screws have become loose and worn 
 from incessant slacking and setting up. 
 
 To Read the Sextant Altitude. — Ascertain by looking toward 
 the left how many degrees and ten-minute divisions the vernier 
 zero has passed on the arc, then look along the vernier to the left 
 until one of its lines coincides exactly with one of the lines of the 
 arc, and the number of vernier minutes and ten-second divisions 
 given will be added to the degrees and minutes originally ob- 
 tained on the arc, and the sum of the two will be the altitude. 
 To this altitude will be applied the index error (if any exists) in 
 order to obtain the corrected observed angle. 
 
 Remarks. — The quadrant, octant, and sextant are constructed 
 on the same principle. Although the real arcs of these instru- 
 
132 the navigator's pocket-book 
 
 ments are respectively only 45°, 60°, and 70°, yet owing to their 
 double reflection they measure angles of 90°, 120°, and 140 c . 
 
 SHADE-GLASSES.— (See Sextant.) 
 
 SHADOW-PIN. — A straight, slender pin arranged to stand 
 vertically on the centre of the glass of the compass bowl. It is 
 portable and is set in place when required for the purpose of 
 obtaining bearings of the sun. As its name indicates, it casts a 
 shadow, and the opposite point of the compass from that on 
 which the shadow falls is accepted as the bearing of the body. 
 The shadow-pin may be employed for taking bearings generally, 
 but it is not as satisfactory as an azimuth attachment or the 
 pelorus. 
 
 SHAPING THE COURSE.— (See Chart Sailing ; Great- 
 Circle Sailing ; Mercator's Sailing ; Middle-Latitude Sailing.) 
 
 SHIP TIME.— The hour shown by the ship's clock, which 
 is set to apparent time or solar time. This may be done roughly 
 by turning the hands of the clock to twelve (noon) when the sun 
 crosses the meridian, or by allowing for the number of miles 
 sailed east or west since the clock was last set. To accomplish 
 this simply add to the face of the clock four minutes of time for 
 every degree sailed east and subtract four minutes for every de- 
 gree sailed west since the clock w r as last set on solar time. The 
 most correct way is to proceed according to the rule given under 
 the head of Regulating. 
 
 SHORE RATE.— (See Rate.) 
 
 SIDEREAL.— Relating to the stars. 
 
 SIDEREAL DAY. — The interval between two successive 
 transits of the same star over the same meridian ; the period of 
 time in which the earth performs a complete revolution on its 
 
THE NAVIGATOR'S POCKET-BOOK 133 
 
 axis. The length of a sidereal day is 23 h. 56 m. 04 sec., so that 
 a sidereal day is shorter than a mean solar day by 3 m. 56 sec. 
 
 SIDEREAL NOON.— This occurs when the First Point of 
 Aries comes to the meridian. 
 
 SIDEREAL TIME.— Time measured by the stars. Sidereal 
 time commences when the .First Point of Aries is on the me- 
 ridian and is counted from one hour to twenty-four hours, when 
 the same point returns to the meridian again. 
 
 SIGHT. — To take a sight is to measure the altitude of a 
 heavenly body. 
 
 SLIDING LIMB.— (See Sextant.) 
 
 SLIP OF WHEEL.— The difference between the speed 
 shown by a steam vessel and the speed that would be attained 
 provided the propeller or paddle-wheels acted upon a solid sub- 
 stance in place of a fluid. Slip of wheel is often referred to as 
 the lost motion of the propeller. It is customary to allow a cer- 
 tain number of revolutions to the mile, and according to this the 
 estimated distance run by the vessel is compared with the actual 
 distance run by observation, and the difference, expressed as a 
 per centum, is entered in the log-book under the head of slip of 
 wheel. Head winds and seas often retard a vessel's speed so that 
 the slip of wheel reaches 50 per cent, and more. 
 
 SOLAR.— Relating to the sun. 
 
 SOLAR DAY. — The time which elapses between two succes- 
 sive transits of the sun over the same meridian. 
 
 SOLAR SYSTEM.— The sun and the heavenly bodies revolv- 
 ing around it ; namely : Mercury, Venus, Earth, Moon, Mars, 
 Jupiter, Saturn, Uranus, and Neptune. 
 
 SOLAR TIME.— Time measured by the sun. When the sun 
 
134 the navigator's pocket-book 
 
 crosses the meridian of the observer it is apparent noon at his 
 place. 
 
 SOLSTICES.— Those times of the year when the sun is at its 
 greatest distance from the equator ; when its declination is 23£° 
 north or 23^° south. 
 
 SPECULUM. — A mirror ; the reflecting glass on an azimuth 
 attachment. 
 
 SPHERE. — According to geography, a representation of the 
 earth's surface, and according to astronomy, the celestial con- 
 cave. 
 
 SPHERICAL.— Globular. 
 
 SPHERICAL SAILINGS.— Great-Circle, Mercator, Middle- 
 Latitude and Parallel Sailings. 
 
 SPHERICAL TRIANGLE.— A portion of the surface of a 
 sphere, contained by the arcs of three great circles. 
 
 SPHERICAL TRIGONOMETRY.— That branch of trig- 
 onometry which deals with the method of solving spherical 
 triangles. 
 
 SPIRIT COMPASS.— A liquid compass. 
 
 SPRING EQUINOX. — When the sun crosses the equator 
 from southern into northern declinations. This is known as the 
 First Point of Aries. The Spring Equinox is often referred to as 
 the Vernal Equinox. (See First Point of Aries.) 
 
 STANDARD COMPASS. — One of the ship's compasses 
 placed where it is least influenced by deviation, and by which 
 the vessel is navigated. 
 
 STANDARD TIME. — Time shown by a watch or clock set 
 to mean solar time. (See Mean Sun.) 
 
THE NAVIGATOR'S POCKET-BOOK 135 
 
 STARS.— (See Fixed Stars.) 
 
 STAR TELESCOPE.— (See Sextant.) 
 
 STAR TIME.— Same as sidereal time. 
 
 STATION POINTER.— An instrument made use of in ma- 
 rine surveying. It consists of a circle of brass graduated in de- 
 grees, and is provided with, one fixed and two movable arms 
 which project from its centre, so that the former may be set to 
 any required angle. It is used sometimes on board ship when 
 sailing along the coast, so as to locate the vessel's position by 
 observing bearings of objects on shore. (See Telemeter.) 
 
 STATUTE MILE.— (See Mile.) 
 
 STEERING COMPASS.— That particular compass referred 
 to by the wheelsman in steering the ship. The vessel is placed 
 on her course by the standard compass, then whatever point is 
 indicated at the time by the steering compass shows the course 
 for the wheelsman to keep the vessel on according to that com- 
 pass. 
 
 STELLAR.— Relating to the stars. 
 
 SUB-PERMANENT MAGNETISM.— After a new iron 
 ship has been launched, it has been found that the magnetism 
 induced in the hull while building rapidly diminishes, but by 
 no means departs entirely, and that which remains is called sub- 
 permanent magnetism. 
 
 SUMNER'S METHOD.— A process employed for finding 
 by a chronometer observation of the sun, or other heavenly 
 body, the true latitude and longitude of the ship, especially when 
 the latitude by dead reckoning cannot be relied upon. This is 
 one of the most valuable problems within the sphere of the 
 navigator, and should be practised by him until proficiency is 
 
13G the navigator's pocket-cook 
 
 attained. In reality it consists of simply working out the lon- 
 gitude several times by either the sun or the moon, a planet or 
 fixed star. In the following we will consider that the sun is 
 employed, consequently the longitudes will be ascertained 
 according to the rule given under the head of "Longitude by 
 One Altitude of the Sun." In case this problem is worked by 
 the moon or by a planet or a star, then the longitudes will be 
 found according to the respective rules given for those bodies 
 under the head of Longitude ; but the lines on the chart will be 
 drawn and the position of the vessel plotted in precisely the 
 same way as described below for the sun. This problem in 
 character is similar to and its result the same as that derived 
 from what is known as the Combined Altitude Problem, or the 
 Double Altitude Problem, but it employs fewer figures and as a 
 natural consequence is simple in comparison and more easily 
 worked than the other. 
 
 Rule. — Assume two latitudes, one 80' (miles) less, and the 
 other 30' greater than the latitude by dead reckoning, then ob- 
 serve a regular time sight of the sun and work it up as usual, 
 employing either of the assumed latitudes, and mark the result 
 on the chart. Now work the same sight over again, using the 
 other assumed latitude. Mark this answer also on the chart and 
 draw a pencil line from one dot to the other. This is known as 
 a line of bearing, and the ship will be somewhere on this line. 
 
 The next thing required is to locate the vessel on this line of 
 bearing. To effect this wait until the sun has changed ils 
 azimuth (bearing) at least 2-J points (four or more would be 
 better) then observe another regular time sight and work it up 
 twice as before, making use of the same two assumed latitudes. 
 Mark these two results on the chart and connect them also with 
 a pencil line, which call the second line of bearing. It will be 
 
POCKET-BOOK 137 
 
 seen that the first and second pencil lines cross one another. 
 Now this intersection points out the ship's place provided she 
 has remained stationary between observations, but if not, then 
 the course and distance sailed after the first observation was 
 taken must be considered as follows : 
 
 Lay off (in pencil) from any part of the first line of bearing 
 the true course and distance sailed in the interval between 
 sights, and through the termination of this course and distance 
 draw a line parallel to the first line of bearing, and where this 
 last line drawn intersects the second line of bearing will be the 
 ship's place. 
 
 Remarks. — Instead of using assumed latitudes 30' different 
 from the latitude by account, the navigator may extend this 
 amount to 1° if he so prefers. 
 
 When the first line is drawn on the chart for the purpose of 
 connecting the first two pencil dots, the navigator knows that 
 lie is somewhere on this line, and provided the line is not paral- 
 lel to the coast, its extension will run into the land, so that if 
 the ship is headed to sail on this line of bearing toward the 
 coast, she will ultimately reach the point into which the line 
 runs. The same applies as well to the second line of bearing. 
 
 It has already been explained that when the second line of 
 bearing has been drawn on the chart, the ship's place is fixed. 
 
 This problem has been styled by some navigators as an astro- 
 nomical cross-bearing. 
 
 SUN. — The centre of the solar system : diameter, 885,000 
 miles ; mean distance from the earth, 95,000,000 miles ; mean 
 apparent diameter, 32' ; circumference, 2,780,000 miles. 
 
 SUN DOG. — A luminous spot occasionally seen in the heavens 
 near the sun. 
 
138 
 
 SUNRISE AND SUNSET SIGHTS.— (See Longitude.) 
 
 SUN TIME. — Same as solar time. 
 
 SWINGING SHIP. — When the vessel is turned in a circle 
 so that her head is brought consecutively to the thirty-two 
 points of the compass, the operation is known as swinging ship. 
 This is performed in compass-adjusting, the purpose being to 
 note, while on each point, the compass-bearing of some distant 
 but well-defined object, the correct magnetic bearing of which 
 is known. 
 
 SYMBOLS.— (See Log Book.) 
 
 TAFFRAIL LOG. — A patent log, the register of which se- 
 cures to the taffrail. (See Patent Log.) 
 
 TAKING DEPARTURE.— (See Departure.) 
 
 TANGENT SCREW.— (See Sextant.) 
 
 TELEMETER. — An instrument consisting of two parallel 
 base bars, divided by scales to tenths of an inch and ranging from 
 to 20 inches on each bar. The object of this instrument is to 
 mechanically solve problems that involve the parts of a plane 
 triangle. It is only of use when sailing along the coast, when 
 it affords a ready means of locating the ship by observing shore 
 bearings, such as light-houses, prominent headlands, etc. 
 
 TELL-TALE. — An inverted compass suspended from over- 
 head in the cabin, or elsewhere below, 
 
 TERRESTRIAL.— Relating to the earth. 
 
 TERTIARY-MERIDIANS.— Those connected with second- 
 ary meridians by carrying time in the most careful manner. (See 
 Secondary Meridians.) 
 
 THERMOMETER. — An instrument used for measuring 
 
THE NAVIGATOR'S POCKET-BOOK 139 
 
 the variations of temperature. Fahrenheit's thermometer is a 
 mercurial column so graduated as to have 180° between the 
 freezing and boiling points of water. The freezing point of 
 water on this thermometer is 32°, and the boiling point 212°. 
 To indicate degrees below zero, it is common to preface them 
 with the minus ( — ) sign. A Centigrade thermometer is a mer- 
 curial column so graduated as to have 100 c between the freezing 
 and boiling points of water, zero being the freezing point. 
 
 To reduce Centigrade reading to Fahrenheit, multiply by 9, 
 divide by 5 and add 32. 
 
 To reduce Fahrenheit to Centigrade, subtract 32, multiply by 
 5 and divide by 9. 
 
 TIME.— (See Apparent, Astronomical, Civil, Greenwich, 
 Local- Apparent, Mean, Mean-Solar, Ship, Sidereal, Solar, Stand- 
 ard, Star, and Sun Times. See also Equation of Time.) 
 
 TIME COURSE —During fog, while navigating in waters 
 where it is necessary to change the course at certain fixed points 
 in order to keep in the channel, or to avoid danger, the employ- 
 ment of time courses becomes imperative. In order to run these, 
 the course and distance from point to point is measured on the 
 chart, and the speed of the vessel taken into account. As soon 
 as the calculated period of time has expired, it is considered that 
 the required distance has been run, and the course is accord- 
 ingly changed. 
 
 If there is a current flowing with, or against, or across the 
 ship's course, the same must be allowed for. 
 
 When threading coral reefs that are submerged, time courses 
 are often employed. 
 
 TIME SIGHT. — An observation of a heavenly bocty taken 
 for the purpose of ascertaining the longitude. (See Longitude.) 
 
140 THE XAVIGATOIi'S POCKET-BOOK 
 
 TRANSIT. — The passage of a heavenly body across the 
 meridian. (See Lower Transit ; Upper Transit,) 
 
 TRAVERSE. — An irregular track made by a vessel on ac- 
 count of having sailed several courses. 
 
 TRAVERSE SAILING.— (See Traverse.) 
 
 TRAVERSE TABLES.— Tables containing the difference 
 of latitude and departure for quarter points and for single de- 
 grees of the compass, calculated for intervals of one mile and 
 extending to three hundred miles. By these tables the solution 
 of right-angle triangles is accomplished by mere inspection. The 
 form that a navigator rules for working out his dead reckoning 
 is a traverse table for the particular courses sailed by his ves- 
 sel. 
 
 TRIGONOMETRY.— The science of measuring triangles. 
 
 TRIPOD COMPASS. — A compass elevated on a three-leg 
 stand, on the principle of the pole compass. 
 
 TROPIC OF CANCER.— The parallel of 23° 28' north— 
 the highest northern point of the sun's declination, which it 
 reaches on June 21st. 
 
 TROPIC OF CAFRICORN.—The parallel of 23° 28' south. 
 — the highest southern point of the sun's declination, which it 
 reaches on December 21st. 
 
 TRUE-CENTRAL-ALTITUDE. — (See Corrected Alti- 
 tude.) 
 
 TYPHOON.— (See Law of Storms.) 
 
 UPPER LIMB. — The highest part of the circumference of 
 the sun and moon ; the part situated directly above the centre- 
 When the image of the lower portion of the disk of the sun or 
 moon is brought in contact with the horizon, it is 'said that the 
 
THE KAVIGATOR'S POCKET-BOOK 141 
 
 altitude of the lower limb is observed, and when the image of 
 the upper portion of the disk is brought in contact with the hori- 
 zon, it is said that the altitude of the upper limb is observed. 
 (See Corrected Altitude.) 
 
 UPPER TRANSIT.— The passage of a heavenly body over 
 the meridian when the body is moving from east to west. The 
 Nautical Almanac gives the astronomical times of the upper 
 transits of heavenly bodies. The body having risen until it 
 crossed the meridian above the pole, while moving from east to 
 west, it declines to the west, then curves eastward, continuing 
 to fall until it crosses the meridian below the pole— 180° distant 
 from the meridian of its upper transit. It then commences to 
 rise, still moving eastward, and when midway between the 
 meridians'of its upper and lower transits, it curves westward 
 and continues to rise until it again makes its upper transit. (See 
 Lower Transit.) 
 
 VARIATION. — The divergence of the compass needle from 
 the true north of the heavens. This is not constant. In the 
 year 1663 in Paris, the needle pointed true north, previous to 
 which the variation had been easterly. From the year 1663 to 
 the year 1814, the westerly variation in Paris steadily increased, 
 until in the latter year it amounted to 22^°. From the year 1814 
 it has steadily decreased, but is still westerly. (See Compass ; 
 Amplitude ; Azimuth.) 
 
 VARIATION CHART.— (See Chart.) 
 
 VERNAL EQUINOX.— (See Spring Equinox.) 
 
 VERNIER. — The graduated scale on the sliding limb or in- 
 dex bar of the sextant. (See Sextant.) 
 
 VERTEX. — That point of the heavens situated perpendicu- 
 
142 the navigator's pocket-book 
 
 larly above the observer's head ; the angular point, or the point 
 where the two legs or sides of an angle meet. 
 
 VERTICAL. — Perpendicular to the horizon. 
 
 VERTICAL CIRCLE.— A great circle of the sphere which 
 passes through the zenith and nadir of a place. 
 
 VERTICAL DANGER ANGLE.— (See Danger Angle.) 
 
 VISIBLE HORIZON.— The boundary or limit of the obser- 
 ver's view is termed the visible or apparent horizon. The angle 
 between the sensible and visible horizons is known as the dip of 
 the horizon. 
 
 WATCHES.— (See Log-Book.) 
 
 WEATHER. — The signs or indications by which the coming 
 weather may be anticipated are as follows : 
 
 A rosy sky at sunset, fine weather ; a bright yellow sky at 
 sunset, wind ; a pale yellow sky at sunset, wet ; orange or cop- 
 per colored sky, wind and rain ; sickly greenish hue, wind and 
 rain ; tawny or coppery clouds, wind ; a dark red sky, rain ; 
 a red sky in the morning, bad weather ; a gray sky in the morn- 
 ing, fine weather ; a high dawn, wind ; a low dawn, fair 
 weather ; soft or delicate clouds, fine weather with light breezes ; 
 hard-edged, oily looking clouds, wind ; a dark, gloomy, blue 
 sky, wind ; light, bright-blue sky, fine weather ; light, delicate 
 tints with soft, indefinite forms of cloud, fine weather ; gaudy 
 or unusual hues with hard, definitely outlined clouds, rain and 
 wind ; small, inky clouds, rain ; high upper clouds crossing the 
 heavens in a direction different from that of the lower clouds, or 
 of the wind felt below, foretell a change of wind in the direc- 
 tion of the upper clouds ; when sea birds fly out far to seaward, 
 moderate wind and fair weather may be expected ; when sea 
 
THE NAVIGATOR'S POCKET-BOOK 143 
 
 birds bang about the land or fly inland, strong winds and stormy- 
 weather are promised ; dew is an indication of coming fine 
 weather. 
 
 Cirrus. — Also known as the mare-tail cloud, composed of 
 streaks, wisps, and fibres ; a cloud of the least density and 
 greatest elevation, showing the widest range of direction and 
 variety of form. Settled weather is to be expected when groups 
 of cirri are to be seen during a gentle wind after severe weather 
 has been experienced. When streaks of cirri extend across the 
 sky conforming to the direction in which a light wind is blow- 
 ing, the wind will remain steady but increase. When fine 
 threads of cirri are blown or brushed backward at one end, the 
 surface wind will veer around to that point. 
 
 Cumulus. — This is also known as the day cloud and the sum- 
 mer cloud. It forms only in the day-time during the summer, 
 and results from the rise of vapors from rivers, lakes, etc., into 
 the colder atmosphere. Fine, calm, and warm weather may be 
 anticipated when cumuli take on a moderate size and delicate 
 color ; but cold, rainy, and heavy weather may be expected 
 when cumuli in dense, dark masses roll acress the sky, sink low- 
 er, and do not disappear at sunset. 
 
 Stratus. — Also called the night cloud. It hangs the lowest of 
 the various clouds, obtains its greatest density about midnight, 
 and disappears when the sun rises. It is formed by the conden- 
 sation of vapors from lakes, marshes, etc., appearing as an ex- 
 tended sheet of white mist near to the earth, and sometimes 
 touching it. 
 
 Cirro-Cumulus. — This is known as well by the name of a 
 mackerel sky. It is seen in small, rounded masses, looking like 
 flocks of sheep lying down, and in consequence is referred to at 
 times as sheep in-a -meadow sky. It is principally seen in summer, 
 
114 THE NAVIGATORS POCKET-BOOK 
 
 and indicates warm, dry, weather. When cirro-cumulus occurs 
 in winter, a thaw and wet weather may be expected. 
 
 Cirro-Stratus. — Also referred to as the vane cloud, the slioal 
 of -fish cloud, and the mackerel-backed cloud. A storm of rain or 
 snow may be expected when this cloud is seen. As it name sig- 
 nifies, this cloud exhibits a mingling of the characteristics of 
 the cirrus and stratus, being dense in the middle and tapering 
 toward the edges. 
 
 Oumulo-Stratus. — A blending or mingling of the cumulus 
 and cirro-stratus, appearing at times as a thick bank of cloud 
 with overhanging edges. What is known as a distinct-cumulo- 
 stratus cloud appears as a cumulus cloud surrounded on all sides 
 by small fleecy clouds. When cumulo-stratus clouds are seen 
 sudden atmospheric changes may be expected. 
 
 Nimbus, or Cumulo-Cirro- Stratus. — Called the rain cloud. 
 As it name signifies, it is a combination of the three primary 
 forms of cloud. The cirro-stratus overspreads the sl^y, and un- 
 derneath it the cumulus clouds drive in from windward until 
 they form one continuous mass, settling down in a horizontal 
 sheet from which rain falls. 
 
 Cloud Scale. — The amount of cloud is denoted by a numer- 
 ical scale of to 10 — indicating a clear sky, 5 a sky half cov- 
 ered, and 10 a totally obscured sky. 
 
 Rainbows. — When rainbows are observed in the morning 
 they promise wet weather, but when observed in the evening 
 they promise clear weather. 
 
 WIND. — The wind, as a rule, shifts with the sun ; but 
 whereas this means from left to right (or with the hands of a 
 clock) in the northern hemisphere, it means from right to left 
 (or against the hands of a clock) in the southern hemisphere. 
 This is known as veering. When the wind shifts in the contrary 
 
THE KAVIGATOir'S POCKET-BOOK 145 
 
 direction it is known as backing. There is an old sea couplet 
 which applies with truthfulness to the shifting of the wind : 
 
 ' ' When the wind shifts against the sun, 
 Trust it not, for back it will run." 
 
 In the northern hemisphere the veering, or proper shifting of 
 the wind would be from east to west by the way of south-east, 
 south, and south-west, and the backing of the wind would be 
 from east to west by the way of north-east, north, and north- 
 west. 
 
 In the southern hemisphere the above rule would be reversed. 
 
 When the wind backs it may be accepted as a sign that the 
 weather is unsettled, and that the wind will come out again from 
 its original quarter. 
 
 Winds are named from the direction in which they blow, 
 hence a north wind comes out of the north. 
 
 ZENITH. — That point in the heavens vertically overhead of 
 the observer, and 90° distant from every point of the horizon. 
 Opposed to nadir. (See Nadir.) 
 
 ZENITH DISTANCE.— What an altitude lacks of 90°, or 
 the complement of an altitude ; the angular distance of a heav- 
 enly body from the zenith of the observer. 
 
 ZERO. — The point at which the cutting or graduation of a 
 sextant, etc., commences. 
 
 ZODIAC — An imaginary zone in the celestial concave in 
 which the sun, moon, and larger planets appear to perform their 
 revolutions. 
 
 ZONE. — There are five zones : the torrid zone extending 
 10 
 
146 the navigator's pocket-book 
 
 from the equator to 23° 28' north and south ; the temperate 
 zones extending from 23° 28' north and south to 66° 32' north 
 and south, and the frigid zones extending from 66° 32' north 
 and south to the poles. 
 
TABLES 
 
 
THE E"AYIGATOR S POCKET-BOOK 
 
 149 
 
 
 
 TABLE OF CORRECTION 
 
 
 
 
 
 
 
 TO BE APPLIED 
 
 TO THE 
 
 
 
 
 
 TRUE ALTITUDE OF THE POLAR STAR. 
 
 
 
 R. A. 
 
 Merid- 
 
 1 
 Cor- 
 rection. J 
 
 R. A. 
 
 Merid- 
 
 Cor- 
 rection. 
 
 R. A. 
 
 Merid- 
 
 Cor- 
 rection. 
 
 R. A. 
 
 Merid- 
 
 Cor- 
 rection. 
 
 ian. 
 
 
 ian. 
 
 
 ian. 
 
 
 ian. 
 
 
 h. m. 
 
 o / 
 
 h. 
 
 m. 
 
 o / 
 
 h. 
 
 m. 
 
 o / 
 
 h. 
 
 m. 
 
 o / 
 
 
 
 -1 10 
 
 6 
 
 00 
 
 — 20 
 
 12 
 
 00 
 
 + 1 10 
 
 IS 
 
 00 
 
 + 26 
 
 10 
 
 -^1 12 
 
 6 
 
 10 
 
 — 23 
 
 12 
 
 10 
 
 + 1 12 
 
 IS 
 
 10 
 
 + 23 
 
 20 
 
 — 1 12 
 
 6 
 
 20 
 
 — 19 
 
 12 
 
 20 
 
 + 1 12 
 
 18 
 
 20 
 
 + 19 
 
 30 
 
 — 1 13 i 
 
 G 
 
 30 
 
 — 10 
 
 12 
 
 30 
 
 + 1 13 
 
 18 
 
 30 
 
 + 16 
 
 40 
 
 — 1 14 | 
 
 
 
 40 
 
 — 13 
 
 12 
 
 40 
 
 + 1 14 
 
 IS 
 
 40 
 
 + 13 
 
 50 
 
 — 1 14 
 
 (5 
 
 50 
 
 — 10 
 
 12 
 
 50 
 
 + 1 14 
 
 18 
 
 50 
 
 + 10 
 
 1 00 
 
 — 1 15 \ 
 
 7 
 
 00 
 
 — 7 
 
 13 
 
 00 
 
 + 1 15 
 
 19 
 
 00 
 
 + 7 
 
 1 10 
 
 — 1 15 
 
 7 
 
 10 
 
 — 3 
 
 13 
 
 10 
 
 + 1 15 
 
 19 
 
 10 
 
 + 3 
 
 1 20 
 
 — 1 15 
 
 7 
 
 20 
 
 
 
 13 
 
 20 
 
 + 1 15 
 
 19 
 
 20 
 
 
 
 1 30 
 
 -1 15 
 
 7 
 
 30 
 
 + 03 
 
 13 
 
 30 
 
 + 1 15 
 
 19 
 
 30 
 
 — 3 
 
 1 40 
 
 -1 15 
 
 7 
 
 40 
 
 + 7 
 
 13 
 
 40 
 
 + 1 15 
 
 19 
 
 40 
 
 — 7 
 
 1 50 
 
 ^-1 14 
 
 7 
 
 50 
 
 + 10 
 
 13 
 
 50 
 
 + 1 14 
 
 19 
 
 50 
 
 — 10 
 
 2 00 
 
 — 1 14 
 
 8 
 
 00 
 
 + 13 
 
 14 
 
 00 
 
 + 1 14 
 
 20 
 
 00 
 
 — 13 
 
 2 10 
 
 — 1 13 
 
 8 
 
 10 
 
 + 10 
 
 14 
 
 10 
 
 + 1 13 
 
 20 
 
 10 
 
 — 16 
 
 2 20 
 
 — 1 12 
 
 8 
 
 2.) 
 
 * 19 
 
 14 
 
 20 
 
 + 1 12 
 
 20 
 
 20 
 
 — 19 
 
 2 30 
 
 — 1 11 
 
 8 
 
 30 
 
 + 23 
 
 14 
 
 30 
 
 + 1 12 
 
 20 
 
 30 
 
 — 23 
 
 2 40 
 
 — 1 10 
 
 8 
 
 40 
 
 + 26 
 
 14 
 
 40 
 
 + 1 10 
 
 20 
 
 40 
 
 — 26 
 
 2 50 
 
 -1 9 
 
 8 
 
 50 
 
 + 29 
 
 14 
 
 50 
 
 + 1 9 
 
 20 
 
 50 
 
 — 29 
 
 3 00 
 
 — 1 8 
 
 9 
 
 00 
 
 + 32 , 
 
 15 
 
 00 
 
 + 18 
 
 21 
 
 00 
 
 — 32 
 
 3 10 
 
 — 1 T 
 
 9 
 
 10 
 
 + 35 ! 
 
 15 
 
 10 
 
 + 1 7 
 
 21 
 
 10 
 
 — 35 
 
 3 20 
 
 — 1 5 
 
 9 
 
 20 
 
 + 37 
 
 15 
 
 20 
 
 + 15 
 
 21 
 
 20 
 
 -0 37 
 
 3 30 
 
 — 1 3 
 
 9 
 
 30 
 
 + 40 
 
 15 
 
 30 
 
 + 13 
 
 21 
 
 30 
 
 — 40 
 
 3 40 
 
 -1 1 
 
 9 
 
 40 
 
 + 43 
 
 15 
 
 40 
 
 + 11 
 
 21 
 
 40 
 
 — 43 
 
 3 50 
 
 — 59 
 
 9 
 
 50 
 
 + 46 
 
 15 
 
 50 
 
 + 59 
 
 21 
 
 50 
 
 — 46 
 
 4 00 
 
 — 57 
 
 10 
 
 00 
 
 + 48 
 
 16 
 
 00 
 
 + 57 
 
 22 
 
 00 
 
 -0 48 
 
 4 10 
 
 — 55 
 
 1 10 
 
 10 
 
 + 51 
 
 16 
 
 10 
 
 + 55 
 
 22 
 
 10 
 
 — 51 
 
 4 20 
 
 — 53 
 
 10 
 
 20 
 
 + 53 
 
 16 
 
 20 
 
 + 53 
 
 22 
 
 20 
 
 — 53 
 
 4 30 
 
 — 51 
 
 10 
 
 30 
 
 + 55 
 
 16 
 
 30 
 
 + 51 
 
 22 
 
 30 
 
 — 55 
 
 4 40 
 
 — 4S 
 
 10 
 
 40 
 
 + 57 
 
 16 
 
 40 
 
 + 48 
 
 22 
 
 40 
 
 — 57 
 
 4 50 
 
 — 4(5 
 
 10 
 
 50 
 
 + 59 
 
 16 
 
 50 
 
 + 46 
 
 22 
 
 50 
 
 — 59 
 
 5 00 
 
 — 43 
 
 11 
 
 00 
 
 + 11 
 
 17 
 
 00 
 
 + 43 
 
 23 
 
 00 
 
 — 1 1 
 
 5 10 
 
 — 40 
 
 11 
 
 10 
 
 + 13 
 
 17 
 
 10 
 
 + 40 
 
 23 
 
 10 
 
 — 1 3 
 
 5 20 
 
 — 37 
 
 11 
 
 20 
 
 + 15 
 
 17 
 
 20 
 
 + 37 
 
 23 
 
 20 
 
 — 15 
 
 5 30 
 
 — 35 
 
 11 
 
 30 
 
 + 17 
 
 17 
 
 30 
 
 + 35 
 
 23 
 
 30 
 
 — 1 7 
 
 5 40 
 
 — 32 
 
 11 
 
 40 
 
 + 1 8 
 
 17 
 
 40 
 
 + 32 
 
 23 
 
 40 
 
 — 1 8 
 
 5 50 
 
 — 29 
 
 11 
 
 50 
 
 + 19 
 
 17 
 
 50 
 
 + 29 
 
 23 
 
 50 
 
 — 1 9 
 
 6 00 
 
 — 26 
 
 12 
 
 00 
 
 + 1 10 
 
 18 
 
 00 
 
 + 26 
 
 24 
 
 00 
 
 — 1 10 
 
150 
 
 THE NAVIGATOR S POCKET-BOOK 
 
 QD 
 
 pq 
 
 < 
 
 < 
 
 CO 
 
 m 
 
 & 
 
 O 
 m 
 & 
 
 H 
 H 
 
 Astronomical Apparent Time of Crossing the Meridian of the Ship. 
 
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 h. m. 
 
 12 37 
 
 2 01 
 15 07 
 21 39 
 
 11 58 
 17 81 
 
 3 14 
 
 13 17 
 15 02 
 
 12 37 
 
 20 48 
 
 14 08 
 23 51 
 
 6 20 
 
 13 50 
 9 02 
 
 21 24 
 
 22 00 
 19 49 
 
 *T "aox 
 
 h. m. h. m. 
 
 16 38 14 41 
 
 6 02 4 05 
 19 08! 17 11 
 
 1 40,23 43 
 
 15 59 14 02 
 21 32 10 35 
 
 7 15 5 18 
 
 17 18 15 21 
 10 03 17 06 
 
 16 38 14 41 
 
 49 22 52 
 IS 09 16 12 
 
 3 52 1 55 
 10 21 8 24 
 
 17 51 15 54 
 13 03 11 06 
 
 1 25 23 28 
 
 2 01 04 
 23 50 21 53 
 
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THE XAVIGATOR S POCKET-BOOK 
 
 151 
 
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152 
 
 THE NAVIGATOR S POCKET-BOOK 
 
 TABLE OF DISTANCES 
 
 At which Objects can be Seen at Sea, according to 
 their respective elevations and the height op the 
 Observer's Eye Above Sea-Level. 
 
 Height 
 
 Distance 
 
 Height 
 
 Distance 
 
 Height 
 
 Distance 
 
 Height 
 
 Distance 
 
 in 
 
 in Nauti- 
 
 in 
 
 in Nauti- 
 
 in 
 
 in Nauti- 
 
 in 
 
 in Nauti- 
 
 Feet. 
 
 cal Miles. 
 
 Feet. 
 
 cal Miles. 
 
 Feet. 
 
 cal Miles. 
 
 Feet. 
 
 cal Miles. 
 
 5 
 
 2.565 
 
 55 
 
 8.509 
 
 110 
 
 12.030 
 
 450 
 
 24.380 
 
 10 
 
 3.628 
 
 60 
 
 8.886 
 
 120 
 
 12.560 
 
 500 
 
 25.650 
 
 15 
 
 4.443 
 
 65 
 
 9.249 
 
 130 
 
 13.080 
 
 550 
 
 26.900 
 
 20 
 
 5.130 
 
 70 
 
 9.598 
 
 140 
 
 13.570 
 
 600 
 
 28.100 
 
 25 
 
 5 736 
 
 75 
 
 9.935 
 
 150 
 
 14.050 
 
 650 
 
 29.250 
 
 80 
 
 6.283 
 
 80 
 
 10.260 
 
 200 
 
 16.220 
 
 700 
 
 30.280 
 
 35 
 
 6.7S7 
 
 85 
 
 10.570 
 
 250 
 
 18.140 
 
 800 
 
 32.450 
 
 40 
 
 7.255 
 
 90 
 
 10.880 
 
 300 
 
 19.870 
 
 900 
 
 34.540 
 
 45 
 
 7.696 
 
 95 
 
 11.180 
 
 350 
 
 21 460 
 
 1,000 
 
 36.280 
 
 50 
 
 8.112 
 
 100 
 
 11 470 
 
 400 
 
 22.940 
 
 * 
 
 * 
 
 Rule. — Add together the figures given for the height of eye 
 above the sea-level and the figures given for the elevation of the 
 object, and the answer will be the distance of the vessel from 
 the object in question. 
 
 "When a low-lying island, or shore, or the hull of a low-sided 
 vessel is seen awash with the horizon, the distance of the hori- 
 zon for the height of the observer's eye above the sea-level will 
 alone give the distance from the object. 
 
 Example.— The top of a lighthouse 150 feet high is seen 
 awash when the observer's eye is 15 feet above the sea-level — 
 required the distance of the observer from the light ? 
 
 Height of eye, 15 feet = 4,443 miles. 
 Height of light, 150 feet = 14,050 miles. 
 
 Distance of observer from light, 18,493 = 18-J miles nearly. 
 
THE NAVIGATOR S POCKET-BOOK 
 
 153 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 
 Heig 
 
 lit of Light Above Sea-Level. 
 
 Distance in 
 
 
 
 
 
 1 ards. 
 
 
 
 
 
 
 30 Feet. 
 
 35 Feet. 
 
 40 Feet. 
 
 45 Feet. 
 
 
 o / // 
 
 o / // 
 
 o / // 
 
 O f ff 
 
 100 
 
 5 42 40 
 
 6 39 20 
 
 7 35 40 
 
 8 31 50 
 
 150.. 
 
 3 48 50 
 
 4 26 50 
 
 5 04 50 
 
 5 42 40 
 
 200 
 
 2 51 40 
 
 3 20 20 
 
 3 48 50 
 
 4 17 20 
 
 250 
 
 2 17 30 
 
 2 40 20 
 
 3 03 10 
 
 3 26 00 
 
 300 
 
 1 54 30 
 
 2 13 40 
 
 2 32 40 
 
 2 51 40 
 
 350 
 
 1 38 10 
 
 1 54 30 
 
 2 10 50 
 
 2 17 10 
 
 400 
 
 1 26 00 
 
 1 40 10 
 
 1 54 30 
 
 2 08 50 
 
 450." 
 
 1 16 20 
 
 1 29 10 
 
 1 41 50 
 
 1 54 30 
 
 500 (im.). 
 
 1 08 40 
 
 1 20 10 
 
 1 31 40 
 
 1 43 10 
 
 550 
 
 1 02 30 
 
 1 12 50 
 
 1 23 20 
 
 1 33 40 
 
 600 
 
 57 20 
 
 1 06 50 
 
 1 16 20 
 
 1 26 00 
 
 650 
 
 52 50 
 
 1 01 40 
 
 1 10 30 
 
 1 19 20 
 
 700 
 
 49 10 
 
 57 20 
 
 1 05 30 
 
 1 13 40 
 
 750 
 
 45 50 
 
 53 30 
 
 1 01 10 
 
 1 08 40 
 
 800 
 
 43 00 
 
 50 10 
 
 57 20 
 
 1 04 30 
 
 850. 
 
 40 30 
 
 47 10 
 
 53 50 
 
 1 00 40 
 
 yoo 
 
 38 10 
 
 44 30 
 
 51 00 
 
 57 20 
 
 950 
 
 36 10 
 
 42 10 
 
 48 10 
 
 54 20 
 
 1000 (|m.) 
 
 34 20 
 
 40 10 
 
 45 50 
 
 51 30 
 
154 
 
 THE NAVIGATORS POCKET-BOOK 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 
 Heig 
 
 lit of Light Above Sea-Level. 
 
 Distance in 
 
 
 
 
 
 1 aids. 
 
 
 
 
 
 
 30 Feet. 
 
 35 Feet. 
 
 40 Feet. 
 
 45 Feet. 
 
 
 o r // 
 
 O 1 II 
 
 o / // 
 
 O 1 II 
 
 1050 
 
 32 40 
 
 38 10 
 
 43 40 
 
 49 10 
 
 1100 
 
 31 10 
 
 36 30 
 
 41 40 
 
 46 50 
 
 1150 
 
 29 50 
 
 34 50 
 
 39 50 
 
 44 50 
 
 1200 
 
 28 40 
 
 33 20 
 
 38 10 
 
 43 00 
 
 1250 
 
 27 30 
 
 32 00 
 
 36 40 
 
 41 10 
 
 1300 
 
 26 30 
 
 30 50 
 
 35 20 
 
 39 40 
 
 1350 
 
 25 30 
 
 29 00 
 
 34 00 
 
 38 10 
 
 1400 
 
 24 30 
 
 28 40 
 
 32 40 
 
 36 50 
 
 1450 
 
 23 40 
 
 Q 27 40 
 
 31 40 
 
 35 30 
 
 1500 (fm.) 
 
 22 50 
 
 26 40 
 
 30 30 
 
 34 20 
 
 1550 
 
 22 10 
 
 25 50 
 
 29 30 
 
 33 20 
 
 1600 
 
 21 30 
 
 25 00 
 
 28 40 
 
 32 10 
 
 1650 
 
 20 50 
 
 24 20 
 
 27 50 
 
 31 10 
 
 1700 
 
 20 10 
 
 23 30 
 
 27 00 
 
 30 20 
 
 1750 
 
 19 40 
 
 22 50 
 
 26 10 
 
 29 30 
 
 1800 
 
 19 10 
 
 22 20 
 
 25 30 
 
 28 40 
 
 1850 
 
 18 30 
 
 21 40 
 
 24 50 
 
 27 50 
 
 1900 
 
 18 10 
 
 21 10 
 
 24 10 
 
 27 10 
 
 1950 
 
 17 40 
 
 20 30 
 
 23 30 
 
 26 30 
 
 2000 (lm.) 
 
 17 10 
 
 20 00 
 
 22 50 
 
 25 50 
 
THE NAVIGATOR S POCKET-BOOK 
 
 155 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Height of Light Above Sea Level. 
 
 Miles 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 50 Feet. 
 
 55 Feet. 
 
 60 Feet. 
 
 65 Feet. 
 
 
 O 1 II 
 
 o / // 
 
 o / // 
 
 o / // 
 
 0.1 
 
 4 45 50 
 
 5 14 10 
 
 5 42 40 
 
 6 11 00 
 
 0.2 
 
 2 23 10 
 
 2 37 30 
 
 2 51 40 
 
 3 06 00 
 
 0.3 
 
 1 35 30 
 
 1 45 00 
 
 1 54 30 
 
 2 04 00 
 
 0.4 
 
 1 11 40 
 
 1 18 50 
 
 1 26 00 
 
 1 33 00 
 
 0.5 
 
 57 20 
 
 1 03 00 
 
 1 08 40 
 
 1 14 30 
 
 0.6 
 
 47 40 
 
 52 30 
 
 57 20 
 
 1 02 00 
 
 0.7 
 
 40 50 
 
 45 00 
 
 49 10 
 
 53 10 
 
 0.8. , 
 
 35 50 
 
 39 20 
 
 43 00 
 
 46 30 
 
 0.9....... 
 
 31 50 
 
 35 00 
 
 38 10 
 
 41 20 
 
 1.0 
 
 28 40 
 
 31 30 
 
 34 20 
 
 37 10 
 
 1.1 
 
 26 00 
 
 28 40 
 
 31 10 
 
 34 00 
 
 1.2 
 
 24 00 
 
 26 20 
 
 28 40 
 
 31 00 
 
 1.3 
 
 22 00 
 
 24 10 
 
 26 30 
 
 28 40 
 
 1.4 
 
 20 30 
 
 22 30 
 
 24 30 
 
 26 40 
 
 1.5 
 
 19 10 
 
 21 00 
 
 22 50 
 
 24 50 
 
 1.6.. 
 
 17 50 
 
 19 40 
 
 21 30 
 
 23 20 
 
 1.7 
 
 16 50 
 
 18 30 
 
 20 10 
 
 21 50 
 
 1.8 
 
 15 50 
 
 17 30 
 
 19 10 
 
 20 40 
 
 1.9 
 
 15 00 
 
 16 30 
 
 18 10 
 
 19 40 
 
 2.0....... 
 
 14 20 
 
 15 40 
 
 17 10 
 
 18 40 
 
156 
 
 THE NAVIGATOR'S POCKET-BOOK 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heig 
 
 it of Light Ahove Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 70 Feet, 
 
 75 Feet. 
 
 80 Feet. 
 
 85 Feet. 
 
 
 o / // 
 
 o / // 
 
 o / // 
 
 o / // 
 
 0.1 
 
 6 39 20 
 
 7 07 30 
 
 7 35 40 
 
 8 03 50 
 
 0.2 
 
 3 20 20 
 
 3 34 30 
 
 3 48 50 
 
 4 03 10 
 
 0.3 
 
 2 13 40 
 
 2 23 10 
 
 2 32 40 
 
 2 42 10 
 
 0.4 
 
 1 40 10 
 
 1 47 20 
 
 1 54 30 
 
 2 01 40 
 
 0.5 
 
 1 20 10 
 
 1 26 00 
 
 1 31 40 
 
 1 37 20 
 
 0.6 
 
 1 06 50 
 
 1 11 40 
 
 1 16 20 
 
 1 21 10 
 
 0.7 
 
 57 20 
 
 1 01 20 
 
 1 05 30 
 
 1 09 30 
 
 0.8 
 
 50 10 
 
 53 40 
 
 57 20 
 
 1 00 50 
 
 0.9 
 
 44 30 
 
 47 40 
 
 51 00 
 
 54 10 
 
 1.0 
 
 40 10 
 
 43 00 
 
 45 50 
 
 48 40 
 
 1.1 
 
 36 30 
 
 39 00 
 
 41 40 
 
 44 20 
 
 1.2 
 
 33 20 
 
 35 50 
 
 38 10 
 
 40 30 
 
 1.3 
 
 30 50 
 
 33 00 
 
 35 10 
 
 37 30 
 
 1.4 
 
 28 40 
 
 30 40 
 
 32 40 
 
 34 50 
 
 1.5 
 
 26 40 
 
 28 40 
 
 30 30 
 
 32 30 
 
 1.6 
 
 25 00 
 
 26 50 
 
 28 40 
 
 30 30 
 
 1.7 
 
 23 40 
 
 25 20 
 
 28 00 
 
 28 40 
 
 1.8 
 
 22 20 
 
 23 50 
 
 25 30 
 
 27 00 
 
 1.9 
 
 21 10 
 
 22 40 
 
 24 10 
 
 25 40 
 
 2.0 
 
 20 00 
 
 21 30 
 
 22 50 
 
 24 20 
 
THE NAVIGATOR 3 POCKET-BOOK 
 
 157 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Height of Light Above Sea-Level. 
 
 Miles 
 and Tenths. 
 
 
 
 
 
 
 
 
 
 70 Feet. 
 
 75 Feet. 
 
 80 Feet. 
 
 85 Feet, 
 
 
 O f ff 
 
 o f ff 
 
 o f ff 
 
 o f ff 
 
 2.1 
 
 19 10 
 
 20 30 
 
 21 50 
 
 23 10 
 
 2.2 
 
 18 10 
 
 19 30 
 
 20 50 
 
 22 10 
 
 2.3 
 
 17 30 
 
 18 40 
 
 20 00 
 
 21 10 
 
 2.4....... 
 
 16 40 
 
 17 50 
 
 19 10 
 
 20 20 
 
 2.5 
 
 16 00 
 
 17 10 
 
 18 20 
 
 19 30 
 
 2.6 
 
 15 20 
 
 16 30 
 
 17 40 
 
 18 40 
 
 2.7 
 
 14 50 
 
 15 50 
 
 17 00 
 
 18 00 
 
 2.8 
 
 14 20 
 
 15 20 
 
 16 20 
 
 17 20 
 
 2.9 
 
 13 50 
 
 14 50 
 
 15 50 
 
 ■0 16 50 
 
 3.0 
 
 13 20 
 
 14 20 
 
 15 20 
 
 16 10 
 
 3.1 
 
 13 00 
 
 14 00 
 
 14 50 
 
 15 40 
 
 3.2 
 
 12 30 
 
 13 30 
 
 14 20 
 
 15 10 
 
 3.3 
 
 12 10 
 
 13 00 
 
 13 50 
 
 14 50 
 
 3.4 
 
 11 50 
 
 12 40 
 
 13 30 
 
 14 20 
 
 3.5 
 
 11 30 
 
 12 20 
 
 13 10 
 
 13 50 
 
 3.6 
 
 11 10 
 
 0.12 00 
 
 12 40 
 
 13 20 
 
 3.7 
 
 10 50 
 
 11 40 
 
 12 20 
 
 13 10 
 
 3.8 
 
 10 30 
 
 11 20 
 
 12 00 
 
 12 50 
 
 3.9 
 
 10 20 
 
 11 00 
 
 11 40 
 
 12 30 
 
 4.0 
 
 10 00 
 
 10 40 
 
 11 30 
 
 12 10 
 
158 
 
 THE NAVIGATOR S POCKET-BOOK 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heig 
 
 lit of Light . 
 
 Above Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 90 Feet. 
 
 95 Feet. 
 
 100 Feet. 
 
 105 Feet. 
 
 
 o / rt 
 
 O f ft 
 
 a i n 
 
 o / // 
 
 0.1 
 
 8 31 50 
 
 8 59 50 
 
 9 27 40 
 
 9 55 30 
 
 0.2 
 
 4 17 20 
 
 4 31 30 
 
 4 45 50 
 
 5 00 00 
 
 0.3 
 
 2 51 40 
 
 3 01 20 
 
 3 10 50 
 
 3 20 20 
 
 0.4 
 
 2 08 50 
 
 2 25 00 
 
 2 23 10 
 
 2 30 20 
 
 0.5 
 
 1 43 10 
 
 1 48 50 
 
 1 54 30 
 
 2 00 20 
 
 0.6. 
 
 1 26 00 
 
 1 30 40 
 
 1 35 30 
 
 1 40 10 
 
 0.7 
 
 1 13 40 
 
 1 17 40 
 
 1 21 50 
 
 1 26 00 
 
 0.8 
 
 1 04 30 
 
 1 08 00 
 
 1 11 40 
 
 1 15 10 
 
 0.9 
 
 57 20 
 
 1 00 30 
 
 1 03 40 
 
 1 06 50 
 
 1.0 
 
 51 30 
 
 54 30 
 
 57 20 
 
 1 00 10 
 
 1.1 
 
 46 50 
 
 49 30 
 
 52 00 
 
 54 40 
 
 1.2 
 
 43 00 
 
 45 20 
 
 47 40 
 
 50 10 
 
 1.3 
 
 39 40 
 
 41 50 
 
 44 00 
 
 46 20 
 
 1.4 
 
 36 50 
 
 38 50 
 
 40 50 
 
 43 00 
 
 1.5 
 
 34 20 
 
 36 20 
 
 38 10 
 
 40 10 
 
 l.G 
 
 32 10 
 
 34 00 
 
 35 50 
 
 37 40 
 
 1.7 
 
 30 20 
 
 32 00 
 
 33 40 
 
 35 20 
 
 1.8 
 
 28 40 
 
 30 10 
 
 31 50 
 
 33 20 
 
 1.9 
 
 27 10 
 
 28 40 
 
 30 10 
 
 31 40 
 
 2.0 
 
 25 50 
 
 27 10 
 
 28 40 
 
 30 00 
 
THE NAVIGATOR'S POCKET-BOOK 
 
 159 
 
 PATTERSON'S DANGER- ANGLE TABLES. 
 
 Distance in 
 
 Heig 
 
 bt of Liglit Above Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 90 Feet. 
 
 95 Feet. 
 
 100 Feet. 
 
 105 Feet. 
 
 
 or?? 
 
 Off/ 
 
 o / // 
 
 Q t ft 
 
 2.1 
 
 24 30 
 
 25 50 
 
 27 20 
 
 28 40 
 
 2.2 
 
 23 30 
 
 24 40 
 
 26 00 
 
 27 20 
 
 2.3 
 
 22 20 
 
 23 40 
 
 24 50 
 
 26 10 
 
 2.4 
 
 21 30 
 
 22 40 
 
 23 50 
 
 25 00 
 
 2.5 
 
 20 40 
 
 21 50 
 
 22 50 
 
 24 00 
 
 2.6 
 
 19 50 
 
 21 00 
 
 22 00 
 
 23 10 
 
 2.7 
 
 19 10 
 
 20 10 
 
 21 10 
 
 22 20 
 
 2.8 
 
 18 20 
 
 19 30 
 
 20 30 
 
 21 30 
 
 2.9 
 
 17 50 
 
 18 50 
 
 19 40 
 
 20 40 
 
 3.0. . ..... 
 
 17 10 
 
 18 10 
 
 19 10 
 
 20 00 
 
 3.1 
 
 16 40 
 
 17 30 
 
 18 30 
 
 19 20 
 
 3.2 
 
 16 10 
 
 17 00 
 
 17 50 
 
 18 50 
 
 3.3 
 
 15 40 
 
 16 30 
 
 17 20 
 
 18 10 
 
 3.4 
 
 15 10 
 
 16 00 
 
 16 50 
 
 17 40 
 
 3.5 
 
 14 40 
 
 15 30 
 
 16 20 
 
 17 10 
 
 3.6 
 
 14 20 
 
 15 10 
 
 15 50 
 
 16 40 
 
 3.7 
 
 14 00 
 
 14 40 
 
 15 30 
 
 16 10 
 
 3.8....... 
 
 13 30 
 
 14 20 
 
 15 00 
 
 15 50 
 
 3.9 
 
 13 10 
 12 50 
 
 14 00 
 13 40 
 
 14 40 
 
 14 20 
 
 15 20 
 15 00 
 
 4.0 
 
160 
 
 THE NAVIGATOR'S POCKET-BOOK 
 
 PATTERSON'S DANGER- ANGLE TABLES. 
 
 Distance in 
 
 Miles 
 and Tenths. 
 
 Height of Light Above Sea-Level. 
 
 110 Feet. 
 
 115 Feet. 
 
 120 Feet. 
 
 125 Feet. 
 
 0.1 
 
 0.2 
 
 0.3 
 
 0.4 
 
 0.5 
 
 O 1 II 
 
 10 23 20 
 5 14 10 
 3 29 50 
 2 37 30 
 
 2 06 00 
 
 Q 1 II 
 
 10 51 00 
 5 28 30 
 3 39 20 
 2 44 40 
 2 11 40 
 
 1 II 
 
 11 18 40 
 5 42 40 
 3 48 50 
 2 51 40 
 2 17 30 
 
 o / // 
 
 11 46 10 
 5 56 50 
 3 58 20 
 
 2 58 50 
 2 23 10 
 
 0.6 
 
 0.7 
 
 0.8 
 
 9 
 
 1 45 00 
 1 30 00 
 1 18 50 
 1 10 00 
 1 03 00 
 
 1 49 50 
 1 34 10 
 1 22 20 
 1 13 10 
 1 05 50 
 
 1 54 30 
 1 38 10 
 1 26 00 
 1 16 20 
 
 1 08 40 
 
 1 59 20 
 1 42 20 
 1 29 30 
 1 19 30 
 1 11 40 
 
 1.0. 
 
 1.1 
 
 1.2 
 
 1.3 
 
 1.4 
 
 1.5 
 
 57 20 
 52 30 
 48 30 
 45 00 
 42 00 
 
 59 50 
 54 50 
 50 40 
 47 00 
 44 00 
 
 1 02 30 
 
 57 20 
 52 50 
 49 10 
 45 50 
 
 1 05 10 
 59 40 
 55 00 
 51 10 
 
 47 40 
 
 1.6 
 
 1.7 
 
 1.8 
 
 1.9 
 
 2.0 
 
 39 20 
 37 00 
 35 00 
 33 10 
 31 30 
 
 41 10 
 38 50 
 36 40 
 34 40 
 33 00 
 
 43 00 
 40 30 
 38 10 
 36 10 
 34 20 
 
 44 50 
 42 10 
 39 50 
 37 40 
 35 50 
 
THE NAVIGATOR S POCKET-BOOK 
 
 161 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heigl 
 
 it of Light Above Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 110 Feet. 
 
 115 Feet. 
 
 120 Feet. 
 
 125 Feet. 
 
 
 f ff 
 
 o t ft 
 
 O / ff 
 
 Q t ft 
 
 2.1 
 
 30 00 
 
 31 20 
 
 32 40 
 
 34 10 
 
 2.2 
 
 28 40 
 
 30 00 
 
 31 10 
 
 32 30 
 
 2.3 
 
 27 20 
 
 28 40 
 
 29 50 
 
 31 10 
 
 2.4 
 
 26 20 
 
 27 30 
 
 28 40 
 
 29 50 
 
 2.5 
 
 25 10 
 
 26 20 
 
 27 30 
 
 28 40 
 
 2.6 
 
 24 10 
 
 25 20 
 
 26 30 
 
 27 30 
 
 2.7 
 
 23 20 
 
 24 20 
 
 25 30 
 
 26 30 
 
 2.8 
 
 22 30 
 
 23 30 
 
 24 30 
 
 25 30 
 
 2.9 
 
 21 40 
 
 22 40 
 
 23 40 
 
 24 40 
 
 3.0 
 
 21 00 
 
 22 00 
 
 22 50 
 
 23 50 
 
 3.1 
 
 20 20 
 
 21 10 
 
 22 10 
 
 23 10 
 
 3.2 
 
 19 40 
 
 20 30 
 
 21 30 
 
 22 20 
 
 3.3 
 
 19 10 
 
 20 00 
 
 20 50 
 
 21 40 
 
 3.4 
 
 18 30 
 
 19 20 
 
 20 10 
 
 21 00 
 
 3.5 
 
 18 00 
 
 18 50 
 
 19 40 
 
 20 30 
 
 3.6 
 
 17 30 
 
 18 20 
 
 19 10 
 
 19 50 
 
 3.7 
 
 17 00 
 
 17 50 
 
 18 30 
 
 19 20 
 
 3.8 
 
 16 30 
 
 17 20 
 
 18 10 
 
 18 50 
 
 3.9 
 
 16 10 
 
 16 50 
 
 17 40 
 
 18 20 
 
 4.0 
 
 15 40 
 
 16 30 
 
 17 10 
 
 17 50 
 
162 
 
 THE NAVIGATOR'S POCKET-BOOK 
 
 PATTERSON'S DANGER- ANGLE TABLES. 
 
 Distance in 
 
 Heig] 
 
 it of Light . 
 
 AJbove Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 130 Feet. 
 
 135 Feet. 
 
 140 Feet. 
 
 145 Feet. 
 
 
 o i n 
 
 Q 1 II 
 
 O 1 II 
 
 O 1 II 
 
 0.1 
 
 12 13 30 
 
 12 40 50 
 
 13 08 00 
 
 13 35 10 
 
 0.2 
 
 6 11 00 
 
 6 25 10 
 
 6 39 20 
 
 6 53 20 
 
 0.3 
 
 4 07 50 
 
 4 17 20 
 
 4 26 50 
 
 4 36 20 
 
 0.4 
 
 3 06 00 
 
 3 13 10 
 
 3 20 20 
 
 3 27 30 
 
 0.5 
 
 2 28 50 
 
 2 34 40 
 
 2 40 20 
 
 2 46 00 
 
 0.6 
 
 2 04 00 
 
 2 08 50 
 
 2 13 40 
 
 2 18 20 
 
 0.7 
 
 1 46 20 
 
 1 50 30 
 
 1 54 30 
 
 1 58 40 
 
 0.8 
 
 1 33 00 
 
 1 36 40 
 
 1 40 10 
 
 1 43 50 
 
 0.9 
 
 1 22 40 
 
 1 26 00 
 
 1 29 10 
 
 1 32 20 
 
 1.0 
 
 1 14 30 
 
 1 17 20 
 
 1 20 10 
 
 1 23 00 
 
 1.1 
 
 1 07 40 
 
 1 10 20 
 
 1 12 50 
 
 1 15 30 
 
 1.2 
 
 1 02 00 
 
 1 04 30 
 
 1 06 50 
 
 1 09 10 
 
 1.3 
 
 57 20 
 
 59 30 
 
 1 01 40 
 
 1 03 50 
 
 1.4 
 
 53 10 
 
 55 10 
 
 57 20 
 
 59 20 
 
 1.5 
 
 49 40 
 
 51 30 
 
 53 30 
 
 55 20 
 
 1.6 
 
 46 30 
 
 48 20 
 
 50 10 
 
 51 50 
 
 1.7 
 
 43 50 
 
 45 30 
 
 47 10 
 
 48 50 
 
 1.8 
 
 41 20 
 
 43 00 
 
 44 30 
 
 46 10 
 
 1.9 
 
 39 10 
 
 40 40 
 
 42 10 
 
 43 40 
 
 2.0 
 
 37 10 
 
 38 40 
 
 40 10 
 
 41 30 
 
THE NAVIGATOK S POCKET-BOOK 
 
 163 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heig 
 
 it of Light Above Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 130 Feet. 
 
 135 Feet. 
 
 140 Feet, 
 
 145 Feet. 
 
 
 o r ft 
 
 O 9 ft 
 
 O / ft 
 
 Q t ft 
 
 2.1 
 
 35 30 
 
 36 50 
 
 38 10 
 
 39 30 
 
 2.2 
 
 33 50 
 
 35 10 
 
 36 30 
 
 37 50 
 
 2.3 
 
 32 20 
 
 33 40 
 
 34 50 
 
 36 10 
 
 2.4 
 
 31 00 
 
 32 10 
 
 33 20 
 
 34 40 
 
 2.5 
 
 29 50 
 
 31 00 
 
 32 00 
 
 33 10 
 
 2.6 
 
 28 40 
 
 29 40 
 
 30 50 
 
 32 00 
 
 2.7 
 
 27 30 
 
 28 40 
 
 29 40 
 
 30 50 
 
 2.8 
 
 26 40 
 
 27 40 
 
 28 40 
 
 29 40 
 
 2.9 
 
 25 40 
 
 26 40 
 
 27 40 
 
 28 40 
 
 3.0 
 
 24 50 
 
 25 50 
 
 26 50 
 
 27 40 
 
 3.1 
 
 24 00 
 
 25 00 
 
 25 50 
 
 26 50 
 
 3.2 
 
 23 20 
 
 24 10 
 
 25 00 
 
 26 00 
 
 3.3 
 
 22 30 
 
 23 30 
 
 24 20 
 
 25 10 
 
 3.4 
 
 21 50 
 
 22 40 
 
 23 30 
 
 24 30 
 
 3.5 
 
 21 20 
 
 22 10 
 
 22 50 
 
 23 40 
 
 3.6 
 
 20 40 
 
 21 30 
 
 22 20 
 
 23 00 
 
 3.7 
 
 20 10 
 
 20 50 
 
 21 40 
 
 22 30 
 
 3.8 
 
 19 40 
 
 20 20 
 
 21 10 
 
 21 50 
 
 3.9 
 
 19 10 
 
 19 50 
 
 20 30 
 
 21 20 
 
 4.0....... 
 
 18 40 
 
 19 20 
 
 20 00 
 
 20 50 
 
164 
 
 THE NAVIGATORS POCKET-BOOK 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heig 
 
 ht of Light Above Sea-Level. 
 
 Miles 
 and Tenths. 
 
 
 
 
 
 150 Feet. 
 
 155 Feet. 
 
 160 Feet. 
 
 165 Feet. 
 
 
 O 1 II 
 
 O t ft 
 
 O 1 II 
 
 O 1 II 
 
 0.1 
 
 14 02 10 
 
 14 29 00 
 
 14 55 50 
 
 15 22 30 
 
 0.2 
 
 7 0? 30 
 
 7 21 40 
 
 7 35 40 
 
 7 49 40 
 
 0.3 
 
 4 45 50 
 
 4 55 20 
 
 5 04 50 
 
 5 14 10 
 
 0.4 
 
 3 34 30 
 
 3 41 40 
 
 3 48 50 
 
 3 56 00 
 
 0.5 
 
 2 51 40 
 
 2 57 30 
 
 3 03 10 
 
 3 08 50 
 
 0.6 
 
 2 23 10 
 
 2 27 50 
 
 2 32 40 
 
 2 37 30 
 
 0.7 
 
 2 02 40 
 
 2 06 50 
 
 2 10 50 
 
 2 15 00 
 
 0.8 
 
 1 47 20 
 
 1 51 00 
 
 1 54 30 
 
 1 58 10 
 
 0.9 
 
 1 35 30^ 
 
 1 38 40 
 
 1 41 50 
 
 1 45 00 
 
 1.0 
 
 1 26 00 
 
 1 28 50 
 
 1 31 40 
 
 1 34 30 
 
 1.1 
 
 1 18 10 
 
 1 20 49 
 
 1 23 20 
 
 1 26 00 
 
 1.2 
 
 1 11 40 
 
 1 14 00 
 
 1 16 20 
 
 1 18 50 
 
 1.3 
 
 1 06 10 
 
 1 08 20 
 
 1 10 30 
 
 1 12 40 
 
 1.4 
 
 1 01 20 
 
 1 03 30 
 
 1 05 30 
 
 1 07 30 
 
 1.5 
 
 57 20 
 
 59 10 
 
 1 01 10 
 
 1 03 00 
 
 1.6 
 
 53 40 
 
 55 30 
 
 57 20 
 
 59 00 
 
 1.7 
 
 50 30 
 
 52 10 
 
 53 50 
 
 55 40 
 
 1.8 
 
 47 40 
 
 49 20 
 
 51 00 
 
 52 30 
 
 1.9.. 
 
 45 10 
 
 46 40 
 
 48 10 
 
 49 40 
 
 2.0 
 
 43 00 
 
 44 20 
 
 45 50 
 
 47 20 
 
THE XAVIGATOR S POCKET-BOOK 
 
 1G5 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Miles 
 and Tenths. 
 
 Height of Light Above Sea-Level. 
 
 150 Feet. 
 
 155 Feet. 
 
 160 Feet, 
 
 165 Feet. 
 
 2.1 
 
 2.2 
 
 2.3 . 
 
 o t if 
 
 40 50 
 39 00 
 37 20 
 35 50 
 34 20 
 
 o / // 
 
 42 20 
 40 20 
 38 40 
 37 00 
 35 30 
 
 o / // 
 
 43 40 
 41 40 
 39 50 
 38 10 
 36 40 
 
 o / // 
 
 45 00 
 43 00 
 41 10 
 39 20 
 37 50 
 
 2.4 
 
 2.5 
 
 2.6 
 
 2.7 
 
 2.8 
 
 2.9 
 
 3.0 
 
 33 00 
 31 50 
 30 40 
 29 40 
 
 28 40 
 
 34 10 
 32 50 
 31 40 
 30 40 
 29 40 
 
 35 20 
 
 34 00 
 32 40 
 31 40 
 30 30 
 
 36 20 
 35 00 
 33 50 
 32 40 
 31 30 
 
 3.1 
 
 3.2 
 
 3.3....... 
 
 3.4 
 
 3.5 
 
 27 40 
 26 50 
 26 00 
 25 20 
 24 30 
 
 28 40 
 27 40 
 26 50 
 26 10 
 25 20 
 
 29 30 
 
 28 40 
 
 27 50 
 27 00 
 26 10 
 
 30 30 
 
 29 30 
 28 40 
 27 50 
 
 27 00 
 
 3.6 
 
 3.7 
 
 3.9 
 
 4.0 
 
 23 50 
 23 10 
 22 40 
 
 22 00 
 21 30 
 
 24 40 
 24 00 
 23 20 
 
 22 50 
 22 10 
 
 25 30 
 24 50 
 24 10 
 23 30 
 22 50 
 
 26 20 
 25 30 
 24 50 
 24 10 
 23 40 
 
166 
 
 THE NAVIGATOR'S POCKET-BOOK 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heig- 
 
 lit of Light Above Sea-Level. 
 
 Miles 
 and Tenths. 
 
 
 
 
 
 
 
 
 
 
 170 Feet. 
 
 175 Feet. 
 
 180 Feet. 
 
 185 Feet. 
 
 
 O / It 
 
 o / // 
 
 o r rr 
 
 o r rr 
 
 0.1 
 
 15 49 10 
 
 16 15 40 
 
 16 42 00 
 
 17 08 10 
 
 0.2 
 
 8 03 50 
 
 8 17 50 
 
 8 31 50 
 
 8 45 50 
 
 0.3 
 
 5 23 40 
 
 5 33 10 
 
 5 42 40 
 
 5 52 00 
 
 0.4 
 
 4 03 10 
 
 4 10 10 
 
 4 17 20 
 
 4 24 30 
 
 0.5 
 
 3 14 40 
 
 3 20 20 
 
 3 26 00 
 
 3 31 40 
 
 0.6 
 
 2 42 10 
 
 2 47 00 
 
 2 51 40 
 
 2 56 30 
 
 0.7 
 
 2 19 00 
 
 2 23 10 
 
 2 27 10 
 
 2 31 20 
 
 0.8 
 
 2 01 40 
 
 2 05 20 
 
 2 08 50 
 
 2 12 30 
 
 0.9 
 
 1 48 10 
 
 1 51 20 
 
 1 54 30 
 
 1 57 40 
 
 1.0 
 
 1 37 20 
 
 1 40 10 
 
 1 43 10 
 
 1 46 00 
 
 1.1 
 
 1 28 30 
 
 1 31 10 
 
 1 33 40 
 
 1 36 20 
 
 1.2 
 
 1 21 10 
 
 1 23 30 
 
 1 26 00 
 
 1 28 20 
 
 1.3 
 
 1 14 50 
 
 1 17 10 
 
 1 19 20 
 
 1 21 30 
 
 1.4 
 
 1 09 30 
 
 1 11 40 
 
 1 13 40 
 
 1 15 40 
 
 1.5 
 
 1 05 00 
 
 1 06 50 
 
 1 08 40 
 
 1 10 40 
 
 1.6 
 
 1 00 50 
 
 1 02 40 
 
 1 04 30 
 
 1 06 10 
 
 1.7 
 
 57 20 
 
 59 00 
 
 1 00 40 
 
 1 02 20 
 
 1.8 
 
 54 10 
 
 55 40 
 
 57 20 
 
 58 50 
 
 1.9 
 
 51 20 
 
 52 50 
 
 54 20 
 
 55 50 
 
 2.0 
 
 48 40 
 
 50 10 
 
 51 30 
 
 53 00 
 
THE XAVIGATOR S POCKET-BOOK 
 
 16? 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heigl 
 
 it of Light Above Sea-Level. 
 
 Allies 
 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 170 Feet. 
 
 175 Feet. 
 
 180 Feet. 
 
 185 Feet. 
 
 
 o i tr 
 
 Of// 
 
 1 It 
 
 or// 
 
 2.1 
 
 46 20 
 
 47 40 
 
 49 10 
 
 50 30 
 
 2.2 
 
 44 20 
 
 45 30 
 
 46 50 
 
 48 10 
 
 2.3 
 
 42 20 
 
 43 40 
 
 44 50 
 
 46 00 
 
 2.4 
 
 40 30 
 
 41 50 
 
 43 00 
 
 44 10 
 
 2.5 
 
 39 00 
 
 40 10 
 
 41 10 
 
 42 20 
 
 2.6 
 
 37 30 
 
 38 30 
 
 39 40 
 
 40 50 
 
 2.7 
 
 36 00 
 
 37 10 
 
 38 10 
 
 39 10 
 
 2.8 
 
 34 50 
 
 35 50 
 
 36 50 
 
 37 50 
 
 2.9 
 
 33 30 
 
 34 30 
 
 35 30 
 
 36 30 
 
 3.0 
 
 32 30 
 
 33 20 
 
 34 20 
 
 35 20 
 
 3.1 
 
 31 20 
 
 32 20 
 
 33 20 
 
 34 10 
 
 3.2 
 
 30 30 
 
 31 20 
 
 32 10 
 
 33 10 
 
 3.3 
 
 29 30 
 
 30 20 
 
 31 10 
 
 32 10 
 
 3.1 
 
 28 40 
 
 29 30 
 
 30 20 
 
 31 10 
 
 3.5 
 
 27 50 
 
 28 40 
 
 29 30 
 
 30 20 
 
 3.6 
 
 27 00 
 
 27 50 
 
 28 40 
 
 29 30 
 
 3.7 
 
 26 20 
 
 27 10 
 
 27 50 
 
 28 40 
 
 3.8 
 
 25 40 
 
 26 20 
 
 27 10 
 
 27 50 
 
 3.9 
 
 25 00 
 
 25 40 
 
 26 30 
 
 27 10 
 
 4.0 
 
 24 20 
 
 25 00 
 
 25 50 
 
 26 30 
 
108 
 
 THE NAVIGATOR S POCKET-BOOK 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Height of Light Above Sea- Level. 
 
 Miles 
 
 
 
 
 and Tenths. 
 
 190 Feet. 
 
 195 Feet. 
 
 200 Feet. 
 
 205 Feet. 
 
 
 1 If 
 
 o / ft 
 
 o r ft j o / // 
 
 0.1 
 
 17 34 20 
 
 18 00 10 
 
 18 26 10 18 51 50 
 
 0.2 
 
 8 59 50 
 
 9 13 50 
 
 9 27 40 
 
 9 41 40 
 
 3 
 
 6 01 30 
 4 31 30 
 
 6 11 00 
 4 38 40 
 
 6 20 20 
 4 45 50 
 
 6 29 50 
 4 53 00 
 
 0.4 
 
 0.5 
 
 3 37 30 
 
 3 43 10 
 
 3 48 50 
 
 3 54 30 
 
 0.6 
 
 3 01 20 
 
 3 06 00 
 
 3 10 50 
 
 3 15 30 
 
 0.7 
 
 2 35 20 
 
 2 39 30 
 
 2 43 30 
 
 2 47 40 
 
 0.8 
 
 2 16 00 
 
 2 19 30 
 
 2 23 10 
 
 2 26 40 
 
 0.9 
 
 2 00 50 
 
 2 04 00 
 
 2 07 20 
 
 2 10 30 
 
 1.0 
 
 1 48 50 
 
 1 51 40 
 
 1 45 30 
 
 1 57 20 
 
 1.1 
 
 1 39 00 
 
 1 41 30 
 
 1 44 10 
 
 1 46 40 
 
 1.2 
 
 1 30 40 
 
 1 33 00 
 
 1 35 30 
 
 1 37 50 
 
 1.3 
 
 1 23 40 
 
 1 26 00 
 
 1 28 10 
 
 1 30 20 
 
 1.4 
 
 1 17 40 
 
 1 19 50 
 
 1 21 50 
 
 1 23 50 
 
 1.5 
 
 1 12 30 
 
 1 14 30 
 
 1 16 20 
 
 1 18 20 
 
 1.6 
 
 1 08 00 
 
 1 09 50 
 
 1 11 40 
 
 1 13 20 
 
 1.7 
 
 1 04 00 
 
 1 05 40 
 
 1 07 20 
 
 1 09 00 
 
 1.8 
 
 1 00 30 
 
 . 1 02 00 
 
 1 03 40 
 
 1 05 10 
 
 1.9 
 
 57 20 
 
 58 50 
 
 1 00 20 
 
 1 01 50 
 
 2.0 
 
 54 30 
 
 55 50 
 
 57 20 
 
 58 40 
 
THE NAVIGATOR S POCKET-BOOK 
 
 169 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heig 
 
 'lit of Light Above Sea-Level. 
 
 Miles 
 
 
 
 
 and Tenths. 
 
 190 Feet. 
 
 195 Feet. 
 
 200 Feet. 
 
 205 Feet. 
 
 
 Q t tf 
 
 o r tf 
 
 Q t ft 
 
 O / tf 
 
 2.1 
 
 51 50 
 
 53 10 
 
 54 30 
 
 56 00 
 
 2.2 
 
 49 30 
 
 50 50 
 
 52 00 
 
 53 20 
 
 2.3 
 
 47 20 
 
 48 30 
 
 49 50 
 
 51 00 
 
 2.4 
 
 45 20 
 
 46 30 
 
 47 40 
 
 49 00 
 
 2.5 
 
 43 30 
 
 44 40 
 
 45 50 
 
 47 00 
 
 2.6 
 
 41 50 
 
 43 00 
 
 44 00 
 
 45 10 
 
 2.7 
 
 40 20 
 
 41 20 
 
 42 30 
 
 43 30 
 
 2.8 
 
 38 50 
 
 39 50 
 
 40 50 
 
 42 00 
 
 2.9 
 
 37 30 
 
 38 30 
 
 39 30 
 
 40 30 
 
 3.0 
 
 36 20 
 
 37 10 
 
 38 10 
 
 39 10 
 
 3.1 
 
 35 10 
 
 36 00 
 
 37 00 
 
 37 50 
 
 3.2 
 
 34 00 
 
 34 50 
 
 35 50 
 
 36 40 
 
 3.3 
 
 33 00 
 
 33 50 
 
 34 40 
 
 35 40 
 
 3.4 
 
 32 00 
 
 32 50 
 
 33 40 
 
 34 30 
 
 3.5 
 
 31 10 
 
 31 50 
 
 32 40 
 
 33 30 
 
 3.6 
 
 30 10 
 
 31 00 
 
 31 50 
 
 32 40 
 
 3.7 
 
 29 20 
 
 30 10 
 
 31 00 
 
 31 40 
 
 3.8 
 
 28 40 
 
 29 20 
 
 30 10 
 
 30 50 
 
 3.9 
 
 27 50 
 
 28 40 
 
 29 20 
 
 30 10 
 
 4.0 
 
 27 10 
 
 28 00 
 
 28 40 
 
 29 20 
 
170 
 
 THE NAVIGATOR S POCKET-BOOK 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Height of Light Above Sea-Level. 
 
 Miles 
 and Tenths. 
 
 
 
 
 
 
 
 
 
 210 Feet. 
 
 215 Feet. 
 
 220 Feet. 
 
 225 Feet. 
 
 
 O f ft 
 
 O f If 
 
 O t It 
 
 O t It 
 
 0.1 
 
 19 17 20 
 
 19 42 50 
 
 20 08 10 
 
 20 30 20 
 
 0.2 
 
 9 56 00 
 
 10 09 30 
 
 10 23 20 
 
 10 37 10 
 
 0.3 
 
 6 39 20 
 
 6 48 40 
 
 6 58 10 
 
 7 07 30 
 
 0.4 
 
 5 00 00 
 
 5 07 10 
 
 5 14 10 
 
 5 21 20 
 
 0.5 
 
 4 00 10 
 
 4 06 00 
 
 4 11 40 
 
 4 17 20 
 
 0.6 
 
 3 20 20 
 
 3 25 00 
 
 3 29 50 
 
 3 34 30 
 
 0.7 
 
 2 51 40 
 
 2 55 50 
 
 2 59 50 
 
 3 04 00 
 
 0.8 
 
 2 30 20 
 
 2 33 50 
 
 2 37 30 
 
 2 41 00 
 
 0.9 
 
 2 13 40 
 
 2 16 50 
 
 2 20 00 
 
 2 23 10 
 
 1.0 
 
 2 00 20 
 
 2 03 10 
 
 2 06 00 
 
 2 08 50 
 
 1.1 
 
 1 49 20 
 
 1 52 00 
 
 1 54 30 
 
 1 57 10 
 
 1.2 
 
 1 40 10 
 
 1 42 40 
 
 1 45 00 
 
 1 47 20 
 
 1.3 
 
 1 32 30 
 
 1 34 40 
 
 1 37 00 
 
 1 39 10 
 
 1.4 
 
 1 26 00 
 
 1 28 00 
 
 1 30 00 
 
 1 32 00 
 
 1.5 
 
 1 20 10 
 
 1 22 10 
 
 1 24 00 
 
 1 26 00 
 
 1.6 
 
 1 15 10 
 
 1 17 00 
 
 1 18 50 
 
 1 20 30 
 
 1.7 
 
 1 10 50 
 
 1 12 30 
 
 1 14 10 
 
 1 15 50 
 
 1.8 
 
 1 06 50 
 
 1 08 30 
 
 1 10 00 
 
 1 11 40 
 
 1.9 
 
 1 03 20 
 
 1 04 50 
 
 1 06 20 
 
 1 07 50 
 
 2.0 
 
 1 00 10 
 
 1 01 30 
 
 1 03 00 
 
 1 04 30 
 
THE NAVIGATOR'S POCKET-BOOK 
 
 171 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance iu 
 
 Heig 
 
 it of Light Above Sea-L 
 
 evel. 
 
 Aliles 
 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 210 Feet. 
 
 215 Feet. 
 
 220 Feet. 
 
 225 Feet. 
 
 
 O t f 
 
 O f ff 
 
 o f ff 
 
 O f ff 
 
 2.1 
 
 57 20 
 
 58 40 
 
 1 00 00 
 
 1 01 20 
 
 2.2 
 
 54 40 
 
 56 00 
 
 57 20 
 
 58 40 
 
 2.3 
 
 52 20 
 
 53 30 
 
 54 50 
 
 66 00 
 
 2.1 
 
 50 10 
 
 51 20 
 
 52 30 
 
 53 40 
 
 2.5 
 
 48 10 
 
 49 20 
 
 50 20 
 
 51 30 
 
 2.6 
 
 46 20 
 
 47 20 
 
 48 30 
 
 49 30 
 
 2.7 
 
 44 30 
 
 45 40 
 
 46 40 
 
 47 40 
 
 2.8 
 
 43 00 
 
 44 00 
 
 45 00 
 
 46 00 
 
 2.9 
 
 41 30 
 
 42 30 
 
 43 30 
 
 44 30 
 
 3.0 
 
 40 10 
 
 41 00 
 
 42 00 
 
 43 00 
 
 3.1 
 
 38 50 
 
 39 40 
 
 40 40 
 
 41 40 
 
 3.2 
 
 37 40 
 
 38 30 
 
 39 20 
 
 40 20 
 
 3.3 
 
 36 30 
 
 37 20 
 
 38 10 
 
 39 00 
 
 3.4 
 
 35 20 
 
 36 10 
 
 37 00 
 
 37 50 
 
 3.5 
 
 34 20 
 
 35 10 
 
 36 00 
 
 36 50 
 
 3.6 
 
 33 20 
 
 34 10 
 
 35 00 
 
 35 50 
 
 3.7 
 
 32 30 
 
 33 20 
 
 34 00 
 
 34 50 
 
 3.8 
 
 31 40 
 
 32 20 
 
 33 10 
 
 33 50 
 
 3.9 
 
 30 50 
 
 31 30 
 
 32 20 
 
 33 00 
 
 4.0 
 
 30 00 
 
 30 50 
 
 31 30 
 
 32 10 
 
172 
 
 THE NAVIGATOR S POCKET-BOOK 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heig 
 
 tit of Light Above Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 230 Feet. 
 
 235 Feet. 
 
 240 Feet, 
 
 245 Feet. 
 
 
 o / rt 
 
 O f ft 
 
 o / tr 
 
 O ' // 
 
 0.1 
 
 20 58 20 
 
 21 23 20 
 
 21 48 00 
 
 22 12 40 
 
 0.2 
 
 10 51 00 
 
 11 04 50 
 
 11 18 40 
 
 11 32 20 
 
 0.3 
 
 7 16 50 
 
 7 26 20 
 
 7 35 40 
 
 7 45 00 
 
 0.4 
 
 5 28 30 
 
 5 35 30 
 
 5 42 40 
 
 5 49 40 
 
 0.5. 
 
 4 23 00 
 
 4 28 40 
 
 4 34 30 
 
 4 40 10 
 
 0.6 
 
 3 39 20 
 
 3 44 00 
 
 3 48 50 
 
 3 53 40 
 
 0.7 
 
 3 08 00 
 
 3 12 10 
 
 3 16 10 
 
 3 20 20 
 
 0.8....... 
 
 2 44 40 
 
 2 48 10 
 
 2 51 40 
 
 2 55 20 
 
 0.9 
 
 2 26 20 
 
 2 29 30 
 
 2 32 40 
 
 2 35 50 
 
 1.0 
 
 2 11 40 
 
 2 14 30 
 
 2 17 30 
 
 2 20 20 
 
 1.1 
 
 1 59 40 
 
 2 02 20 
 
 2 05 00 
 
 2 07 30 
 
 1.2 
 
 1 49 50 
 
 1 52 10 
 
 1 54 30 
 
 1 57 00 
 
 1.3 
 
 1 41 20 
 
 1 43 30 
 
 1 45 40 
 
 1 48 00 
 
 1.4 
 
 1 34 10 
 
 1 36 10 
 
 1 38 10 
 
 1 40 10 
 
 1.5 
 
 1 27 50 
 
 1 29 40 
 
 1 31 40 
 
 1 33 30 
 
 1.6 
 
 1 22 20 
 
 1 24 10 
 
 1 26 00 
 
 1 27 40 
 
 1.7 
 
 1 17 30 
 
 1 19 10 
 
 1 20 50 
 
 1 22 30 
 
 1.8 
 
 1 13 10 
 
 1 14 50 
 
 1 16 20 
 
 1 18 00 
 
 1.9 
 
 1 09 20 
 1 05 50 
 
 1 10 50 
 
 1 07 20 
 
 1 12 20 
 1 08 40 
 
 1 13 50 
 1 10 10 
 
 2.0 
 
THE NAVIGATOR S POCKET-BOOK 
 
 173 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heig 
 
 lit of Light Above Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 230 Feet. 
 
 235 Feet, 
 
 240 Feet. 
 
 245 Feet. 
 
 
 0/1/ 
 
 o / // 
 
 O / // 
 
 O / // 
 
 2.1 
 
 1 02 40 
 
 1 04 10 
 
 1 05 30 
 
 1 06 50 
 
 2.2 
 
 59 50 
 
 1 01 10 
 
 1 02 30 
 
 1 03 50 
 
 2.3 
 
 57 20 
 
 58 30 
 
 59 50 
 
 1 01 00 
 
 2.4 
 
 54 50 
 
 56 10 
 
 57 20 
 
 58 30 
 
 2.5 
 
 52 40 
 
 53 50 
 
 55 00 
 
 56 10 
 
 2.6 
 
 50 40 
 
 51 50 
 
 52 50 
 
 54 00 
 
 2.7 
 
 48 50 
 
 49 50 
 
 51 00 
 
 52 00 
 
 2.8 
 
 47 00 
 
 48 00 
 
 49 10 
 
 50 10 
 
 2.9 
 
 45 30 
 
 46 30 
 
 47 20 
 
 48 20 
 
 3.0 
 
 43 50 
 
 44 50 
 
 45 50 
 
 46 50 
 
 3.1 
 
 0. 42 30 
 
 43 30 
 
 44 20 
 
 45 20 
 
 3.2 
 
 41 10 
 
 42 00 
 
 43 00 
 
 44 00 
 
 3.3 
 
 40 00 
 
 40 50 
 
 41 40 
 
 42 30 
 
 3.4 
 
 38 40 
 
 39 40 
 
 40 30 
 
 41 20 
 
 3.5 
 
 37 40 
 
 38 30 
 
 39 20 
 
 40 10 
 
 3.G 
 
 36 40 
 
 37 20 
 
 38 10 
 
 39 00 
 
 3.7... 
 
 35 40 
 
 36 20 
 
 37 10 
 
 38 00 
 
 3.8 
 
 34 40 
 
 35 30 
 
 36 10 
 
 37 00 
 
 3.9 
 
 33 50 
 
 34 30 
 
 35 10 
 
 36 00 
 
 4.0 
 
 33 00 
 
 33 40 
 
 34 20 
 
 35 10 
 
174 
 
 THE NAVIGATOR'S POCKET-BOOK 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Heig 
 
 it of Light Above Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 250 Feet. 
 
 260 Feet. 
 
 270 Feet. 
 
 280 Feet, 
 
 
 O t It 
 
 O / // 
 
 O ' // 
 
 / // 
 
 0.1 
 
 22 37 10 
 
 23 25 40 
 
 24 13 40 
 
 25 01 00 
 
 0.2 
 
 11 46 10 
 
 12 13 30 
 
 12 40 50 
 
 13 08 00 
 
 0.3 
 
 7 54 30 
 
 8 13 10 
 
 8 31 50 
 
 8 50 30 
 
 0.4 
 
 5 56 50 
 
 6 11 00 
 
 6 25 10 
 
 6 39 20 
 
 0.5 
 
 4 45 50 
 
 4 57 10 
 
 5 08 30 
 
 5 20 00 
 
 0.6 
 
 3 58 20 
 
 4 07 50 
 
 4 17 20 
 
 4 26 50 
 
 0.7 
 
 3 24 20 
 
 3 32 30 
 
 3 40 40 
 
 3 48 50 
 
 0.8 
 
 2 58 50 
 
 3 06 00 
 
 3 13 10 
 
 3 20 20 
 
 0.9 
 
 2 39 00- 
 
 2 45 20 
 
 2 51 40 
 
 2 58 10 
 
 1.0 
 
 2 23 10 
 
 2 28 50 
 
 2 34 40 
 
 2 40 20 
 
 1.1 
 
 2 10 10 
 
 2 15 20 
 
 2 20 30 
 
 2 25 40 
 
 1.2 
 
 1 59 20 
 
 2 04 10 
 
 2 08 50 
 
 2 13 40 
 
 1.3 
 
 1 50 10 
 
 1 54 30 
 
 1 59 00 
 
 2 03 20 
 
 1.4 
 
 1 42 20 
 
 1 46 20 
 
 1 50 30 
 
 1 54 30 
 
 1.5 
 
 1 35 30 
 
 1 39 20 
 
 1 43 10 
 
 1 46 50 
 
 1.6 
 
 1 29 30 
 
 1 33 00 
 
 1 36 40 
 
 1 40 10 
 
 1.7 
 
 1 24 10 
 
 1 27 40 
 
 1 31 00 
 
 1 34 20 
 
 1.8 
 
 1 19 30 
 
 1 22 40 
 
 1 26 00 
 
 1 29 10 
 
 1.9 
 
 1 15 20 
 
 1 18 20 
 
 1 21 20 
 
 1 24 30 
 
 2.0 
 
 1 11 40 
 
 1 14 30 
 
 1 17 20 
 
 1 20 10 
 
THE NAVIGATOR S POCKET-BOOK 
 
 175 
 
 PATTERSON'S DANGER- ANGLE TABLES. 
 
 Distance in 
 
 Height of Light Above Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 250 Feet. 
 
 260 Feet. 
 
 270 Feet, 
 
 280 Feet. 
 
 
 O 1 It 
 
 ota 
 
 o / // 
 
 o / // 
 
 2.1 
 
 1 08 10 
 
 1 11 00 
 
 1 13 40 
 
 1 16 20 
 
 2.2 
 
 1 05 10 
 
 1 07 40 
 
 1 10 20 
 
 1 12 50 
 
 2.3 
 
 1 02 20 
 
 1 04 50 
 
 1 07 10 
 
 1 09 40 
 
 2.4 
 
 59 40 
 
 1 02 00 
 
 1 04 30 
 
 1 06 50 
 
 2.5 
 
 57 20 
 
 59 30 
 
 1 01 50 
 
 1 04 10 
 
 2.6 
 
 55 00 
 
 57 20 
 
 59 30 
 
 1 01 40 
 
 2.7 
 
 53 00 
 
 55 10 
 
 57 20 
 
 59 20 
 
 2.8 
 
 51 10 
 
 53 10 
 
 55 10 
 
 57 20 
 
 2.9 
 
 49 20 
 
 51 20 
 
 53 20 
 
 55 20 
 
 3.0 
 
 47 40 
 
 49 40 
 
 51 30 
 
 53 30 
 
 3.1 
 
 46 10 
 
 48 00 
 
 49 50 
 
 51 40 
 
 3.2 
 
 44 50 
 
 46 30 
 
 48 20 
 
 50 10 
 
 3.3 
 
 43 20 
 
 45 10 
 
 46 50 
 
 48 40 
 
 3.4 
 
 42 10 
 
 43 50 
 
 45 30 
 
 47 10 
 
 3.5 
 
 40 50 
 
 42 30 
 
 44 10 
 
 45 50 
 
 3.6 
 
 39 50 
 
 41 20 
 
 43 00 
 
 44 30 
 
 3.7 
 
 38 40 
 
 40 20 
 
 41 50 
 
 43 20 
 
 3.8 
 
 37 40 
 
 39 10 
 
 40 40 
 
 42 10 
 
 3.9 
 
 36 40 
 
 38 10 
 
 39 40 
 
 41 10 
 
 4.0 
 
 35 50 
 
 37 10 
 
 38 40 
 
 40 10 
 
176 
 
 THE KAVIGATOR S POCKET-BOOK 
 
 PATTERSON'S DANGEPv-ANGLE TABLES. 
 
 Distance in 
 
 Heig 1 
 
 it of Light Above Sea-Level. 
 
 Miles 
 
 
 
 
 
 and Tenths. 
 
 
 
 
 
 
 290 Feet. 
 
 300 Feet. 
 
 310 Feet, 
 
 320 Feet. 
 
 
 Of// 
 
 o r ir 
 
 o / II 
 
 Of n 
 
 0.1....... 
 
 25 30 00 
 
 26 15 50 
 
 27 01 00 
 
 27 45 30 
 
 0.2 
 
 13 24 50 
 
 13 51 30 
 
 14 18 10 
 
 14 44 40 
 
 0.3 
 
 9 02 00 
 
 9 20 20 
 
 9 38 40 
 
 9 57 00 
 
 0.4 
 
 6 48 00 
 
 7 02 00 
 
 7 15 50 
 
 7 29 40 
 
 0.5 
 
 5 27 00 
 
 5 38 10 
 
 5 49 20 
 
 6 00 30 
 
 0.6 
 
 4 32 40 
 
 4 42 00 
 
 4 51 30 
 
 5 00 50 
 
 0.7.. 
 
 3 53 50 
 
 4 01 50 
 
 4 10 00 
 
 4 18 00 
 
 0.8 
 
 3 24 40 
 
 3 31 50 
 
 3 38 50 
 
 3 45 50 
 
 0.9 
 
 3 02 00 
 
 3 08 20 
 
 3 14 30 
 
 3 20 50 
 
 1.0 
 
 2 43 50 
 
 2 49 30 
 
 2 55 10 
 
 3 00 50 
 
 1.1 
 
 2 29 00 
 
 2 34 10 
 
 2 39 10 
 
 2 44 20 
 
 1.2 
 
 2 16 30 
 
 2 21 20 
 
 2 26 00 
 
 2 30 40 
 
 1.3 
 
 2 06 00 
 
 2 10 20 
 
 2 14 50 
 
 2 19 10 
 
 1.4 
 
 1 57 00 
 
 2 01 10 
 
 2 05 10 
 
 2 09 10 
 
 1.5 
 
 1 49 20 
 
 1 53 00 
 
 1 56 50 
 
 2 00 30 
 
 1.6 
 
 1 42 30 
 
 1 46 00 
 
 1 49 30 
 
 1 53 00 
 
 1.7 
 
 1 36 30 
 
 1 39 40 
 
 1 43 00 
 
 1 46 20 
 
 1.8 
 
 1 31 00 
 
 1 34 10 
 
 1 37 20 
 
 1 40 30 
 
 1.9 
 
 1 26 20 
 
 1 29 10 
 
 1 32 10 
 
 1 35 10 
 
 2.0 
 
 1 22 00 
 
 1 24 50 
 
 1 27 40 
 
 1 30 30 
 
THE NAVIGATOR S POCKET-BOOK 
 
 177 
 
 PATTERSON'S DANGER-ANGLE TABLES. 
 
 Distance in 
 
 Miles 
 and Tenths. 
 
 Height of Light Above Sea-Level. 
 
 290 Feet. 
 
 300 Feet. 310 Feet. 
 
 320 Feet, 
 
 2.1 
 
 2.2 
 
 2.3 
 
 2.4 
 
 2.5 
 
 / ft 
 
 1 18 00 
 1 14 30 
 1 11 20 
 1 08 20 
 1 05 30 
 
 Q f ff 
 
 1 20 50 
 1 17 00 
 1 13 40 
 1 10 40 
 
 1 07 50 
 
 / ff 
 
 1 23 30 
 1 19 40 
 1 16 10 
 1 13 00 
 1 10 10 
 
 f ff 
 
 1 26 10 
 1 22 10 
 1 18 40 
 1 15 20 
 1 12 20 
 
 2.6 
 
 2.7 
 
 2.8 
 
 2.9 
 
 1 03 00 
 1 00 40 
 58 30 
 56 30 
 54 40 
 
 1 05 10 
 1 02 50 
 1 00 30 
 58 30 
 56 30 
 
 1 07 20 
 1 04 50 
 1 02 40 
 1 00 30 
 
 58 20 
 
 1 09 30 
 1 07 00 
 1 04 40 
 1 02 20 
 
 1 00 20 
 
 3.0 
 
 3.1 
 
 3.2 
 
 3.3 
 
 3.4 
 
 3.5 
 
 52 50 
 51 10 
 49 40 
 
 48 10 
 46 50 
 
 54 40 
 53 00 
 51 20 
 
 49 50 
 48 30 
 
 b6 30 
 54 50 
 53 10 
 51 30 
 
 50 00 
 
 58 20 
 56 30 
 54 50 
 53 10 
 51 40 
 
 3.6 ..". 
 
 3.7 
 
 3.8 
 
 3.9 
 
 4.0 
 
 45 30 
 44 20 
 43 10 
 42 00 
 41 00 
 
 47 10 
 45 50 
 44 40 
 43 30 
 42 20 
 
 48 40 
 47 20 
 46 10 
 45 00 
 43 50 
 
 50 10 
 48 50 
 47 40 
 46 20 
 45 10 
 
 12 
 
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