'■ANDTHE' RISE OF MODERN CHEMISTRY ROSCOE CORNELL UNIVERSITY LIBRARY FROM The Estate of S.H. G-age Cornell University Library QD 22.D2R7 John Dalton and the rise of modern chemi .T 1P?4 nn? flfi? 300 The original of tliis book is in tlie Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924002962300 THE CENTUBY SCIENCE SERIES Edited bt SIB HEfTBY E. BOSOOE, D.O.L., LL.D., F.R.a. JOHN DALTON AND THE RISE OF MODERN CHEMISTRY .j^i " INTRODUCTION. In the vestibule of the Manchester Town Hall are placed two life-sized marble statues facing each other. One of" these is that of John Dalton, by Chantrey ; the other that of James Prescott Joule, by Gilbert. Thus honour is done to Manchester's two greatest sons — to Dalton, the founder of modern Chemistry and of the Atomic Theorj^, and the dis- coverer of the laws of chemical-combining propor- tions; to Joule, the founder of modern Physics and the discoverer of the law of the Conservation of Energy. The one gave to the world the final and satisfactory proof of the great principle, long sur- mised and often dwelt upon, that in every kind of chemical change no loss of matter occurs ; the other proved that in all the varied modes of physical change no loss of energy takes place. Dalton, by determining the relative weights of the atoms which 8 JOHN DALTON. take part in chemical change, proved that every such change — whether from visible to invisible, from solid to liquid, or from liquid to gas — can be represented quantitatively by a chemical equa- tion; and he created the Atomic Theory of Chem- istry by which these changes are explained. Joule, by exact experiment, proved the truth of the same statement for the different forms of energy. As we can neither create nor destroy matter, so also we can neither create nor destroy energy. As when the candle burns and the wax disappears, its constituent parts are not lost, but escape in the form of steam and carbonic acid gas formed by the union of the hydrogen and carbon of the wax with atmos- pheric oxygen; so the energy of the chemical forces locked up, or potential, in the wax and oxygen be- comes evident, or kinetic, in the heat of the flame. In other words, the molecular motion of the par- ticles becomes motion of the mass. And just as there is a definite and unalterable relation of weight between the carbon and the hydrogen of the wax and the products of their combustion — carbonic acid and water — so there is a definite and unalter- able relation between the amount of the chemical INTEODTJCTION. 9 potential energy of the constituents of tne wax, and that of the heat evolved by their oxidation. Each relation can be expressed by numbers, and these numbers are the Foundation Constants of science. By the determination of the combining weights of the elements, and of their compounds, Dalton ascertained the truth of the first principle. By rigorous experiment. Joule measured the me- chanical equivalent of heat, and proved that a weight of 772 lbs. falling through the space of one foot developed a fixed and unalterable amount of heat capable of raising the temperature of one pound of water one degree Fahrenheit — thus prov- ing the truth of the second. Before John Dalton's discovery of the laws of chemical combination, and without his Atomic Theory to explain those laws, Chemistry as an exact science did not exist, because although many facts were known, the relation between these facts was unknown. Thus before Dalton's time, although a chemist might predicate the kind of action which occurs when two chemical substances are brought together, no one could calculate with precision how much of each ingredient is required to build up the 10 JOHN D ALTON. new body. After Dalton's work such a calculation became easy and certain. Hence it is that Dalton may truly be said to be the founder of modem Chemistry. As with the indestructibility of mat- ter, so with the indestructibility of energy. What Dalton did for the first great principle, Joule ac- complished for the second; and he is therefore the founder of modern Physics. And thus the great twin brethren of Manchester did work for the world the like of which hath not been seen, and the im- portance of which cannot be reckoned. It is sufficiently remarkable that England should have produced two such men; still stranger might it seem that they arose in the midst of a population given up to industrial pursuits, where the noise of the loom and the spinning- jenny was heard in the land, and where most men's thoughts were engrossed in what shallow minds often look upon as common trade avocations. But quiet corners were in those days, and are even now, to be found in Manchester ; and it may well be argued whether the distant roll of the loaded waggon, the hum of the mill, or even the screech of the locomotive, with all the stir and energy at work within the busy hive of a great INTBODUCTION. 11 industrial centre which those sounds imply, are not, after all, conducive to work of another and a more abstruse character. Whether, in fact, Dalton and Joule would have accomplished their life-work more fully had they been born to the intellectual purple of the ancient universities, and had to spend their time amidst the, to many minds, somewhat ener- vating influences of college life, instead of in the more robust and stimulating air of sturdy northern independence and intelligent northern activity. If, as it is said, the world is ruled by ideas, noth- ing can surely be more appropriate than the position, in the centre of the municipal life of the northern metropolis, accorded to the statues of these two Man- chester men. For upon the work of Dalton and Joule depends success or failure, according as the principles laid down by them are respected or neglected, of all the thousand and one industrial undertakings of that, as of every other community, which follow either the chemical change of one form of matter into another, or the conversion of heat, electricity, or other forms of energy into mechanical work or vice versd. Just as the different branches of science overlap. 12 JOHN DALTON. and as there is no strictly dividing-line between them, one following on and depending on the other, so the work of one of these Manchester men follows naturally on that of the other. Joule was the pupil and the scientific son of Dalton; he inherited the scientific spirit, and carried out the methods of investigation of his master with added refinement and knowledge. It is with the life and work of the elder of these two giants of science that we have in these pages to do. In telling the life-tale of scientific men, the biographer has often little to do beyond chronicling their researches and noting the infiuence which their work exerted on the progress of natural knowledge. Most of such men live uneventful lives; their per- sonal history is not unfrequently of but slight inter- est to the general reader; sometimes it is even com- monplace ; their work has lain in the laboratory or the observatory, where the even tenor of their days is only broken by the discovery of a new law, of a new element, or of a new planet. In Dalton's case this rule does not apply. For although so devoted to his science that he used to say he had no time to get married, and although the INTKODUCTION. 13 greater part of his life was uneventful, spent as it was in working and teaching in a more or less humble way in a provincial town, yet his character presents so many varied aspects, and exhibits such originality, that, apart altogether from his scientific labours, and independently of his position as one of the world's great chemists, the life of the individual man is a study full of interest. Several memoirs of John Dalton have been pub- lished. The first by his friend and pupil, the late Dr. William Charles Henry, F.R.S., printed for the Cavendish Society. A second by the late Dr. Angus Smith, F.R.S., published by the Philosophical Society of Manchester, of which Society Dalton was so long the distinguished President. And a third by my late talented friend Dr. Lonsdale, of Carlisle — being one of his series of Lives of Cumberland Worthies ; for Dalton, as we shall see, was born in that county, although he passed most of his life in Manchester. In this last volume the story is so clearly told, and the pa,ges so often lightened by the true Cumbrian humour of the writer, that I cannot expect to do much more than follow where he has led, and place before, I hope, a somewhat larger 14 JOHN DALTON. audience than he appealed to, and in a more con- densed form, the chief points of interest in John Dalton's life, both as a man and as a chemist. The following is a complete list of memoirs and of notices of Dalton's life: — W. C. Henry, " Memoirs of Life and Scientific Eesearches of J. Dalton" (1854). E. A. Smith, "Memoir of J. Dalton" (1856). H. Lonsdale, " Worthies of Cumberland : Dalton " (1874). J. Harland, "Manchester Collectanea" (Vol. II. p. 232). C. Wheeler, "Manchester" (1836). v. Espinasse, " Lancashire Worthies." Second Series. "Annual Monitor" of Society of Triends (1845, p. 40). JOHN DALTON AND THE RISE OF MODERN CHEMISTRY. CHAPTER I. EARLY LIFE. Passing in the train from Carlisle to Cockermouth, after a journey of about thirty miles, the station of Brigham is reached, and thence a short walk leads to the village of Eaglesfield, where John Dalton was born about the 6th of September, 1766. There stands the first Meeting-house established in Cumberland by the Society of Friends, and there under the grassy turf lie the forbears of the Dalton family, for on both sides Dalton's parents were Quakers. The house in which he was born was a thatched cottage ; now its exterior has been modernised; but inside the dwelling is still much in the condition in which it stood one hundred and thirty years ago, when occu- pied by Joseph Dalton, the hand-loom weaver, and his " gudewife " Deborah, the parents of the chemist. 15 16 JOHN DALTON. Lately, it is satisfactory to learn, a tablet recording this cottage as Dalton's birthplace has been placed by some appreciative friends on its walls. Like most of the Cumberland cottages, a porch stood in front of the door, with slabs of slate on which the pans and other household vessels are placed to air. On opening the door a small square kitchen or "house-part" is seen, where the family lived, and where Joseph Dalton had his loom. Further on is a small sleeping-room, fifteen feet long by six feet high and wide. Here may be seen the recess in which was placed the chaff bed where the couple lay, and here their son John was born. The craft of the father was one common enough in the north of Eng- land a century ago. All the country people wore home-made cloth and home-spun linen. The "grey coats of Cumberland" was a well-known appellation for sturdy Liberal opinion, and many a political battle was in those days fought in the "old grey stuff." For ordinary wear the wool was subjected to little dress- ing, but spun on the " large wheels " found in every cottage, and then woven into stuff on the loom, with which Joseph Dalton earned a somewhat precarious pittance. In spite of his modest earnings — for he seems, as Lonsdale says, to have been a " feckless " kind of man — he pricked up courage to go as far as Caldbeck to court Deborah Greenup, who came of an old " Statesman " Quaker stock, and whom he married at Cockermouth Meeting-house on June 10th, 1755. LIFE AT BAGLESFIELr). 17 Deborah was of an active habit, and from her, rather than from his father, it doubtless was, as is generally said to be the case, that Dalton inherited much of his peculiar power. Three children of the marriage lived to a good old age, three others died early. The three who lived were Jonathan, Mary, and John. Jonathan was the eldest son; but where in the family John came no one knows, for singularly enough, no register of his birth has been found. The Quakers do not practise any baptismal rites, although the births of their children are, as a rule, duly registered. There was, of course, no entry of the birth in the Parish Church books, and so the date of John's entrance into the world remained undiscovered, and was unknown to himself, until after he had become famous, when some inquiries at his birthplace elicited the fact that he probably first saw light on the 6th September, 1766. A century and a half ago the Cumbrian Quaker schoolmasters were far superior in mental capability and in scholastic discipline to the ordinary run of north-country teachers. To such a master Dalton was fortunately sent, and to the early training which he received from Mr. Fletcher he himself ascribes much of his subsequent success in life. Not a brilliant or quick boy, Dalton showed in these first years germs of that steadfastness of pur- pose and power of abstract thought which made him great. In a letter written in 1832, Dalton himself describes this part of his early life as follows: — B 18 JOHN BALTON. "The writer of this was born at Eaglesfield, near Cockermouth, Cumberland. Attended the village schools there, and in the neighbourhood, till eleven years of age, at which period he had gone through a course of mensuration, surveying, navigation, etc." The Quaker schoolmaster, Fletcher, was evidently a superior kind of man, and not one of the old sort who hammered the Latin grammar into the boys' heads by a process of birching elsewhere. Who knows whether the boy of nine, if he had received such a treatment instead of being put on to mathe- matics, the foundation of all natural knowledge, would ever have left his native uplands. But this was not to be, and young Dalton not only attracted the attention of his schoolmaster, but that of another remarkable Eaglesfield man, who first became his patron and then his fast friend for life. And nothing strikes one as more remarkable in this remarkable life than that in this remote Cumberland village should be found, in the middle of last century, a Quaker gentleman of means, of scientific and literary ability far above the average of men living in more favoured centres. Mr. Elihu Robinson was a capable meteorologist, probably the first in Cumberland ; the was also a skilled instrument-maker, and corresponded with men like Franklin and Clarkson. Indeed, the existence of such highly cultured, liberal-minded Quakers was no uncommon thing in West Cumber- land in those early days. Earnest in well-doing, these LIFE AT BAGLESPIELD. 19 men stood in the forefront of every liberal movement, and exerted a beneficial influence not only in their own district, but over a much wider area. The friend- ship and intercourse enjoyed by the poor weaver's son with Elihu Robinson were conditions admirably suited to advance and stimulate Dalton's powers ; for he as- sisted the boy in his studies, and taught him, along with a young man twice his age but with not half his power. Mr. Robinson would often set the boys ques- tions in mathematics, and after they had puzzled over the problem for some time, Dalton's companion would propose to ask for the solution, whereat Dalton, show- ing the reliance on his own powers which was one great characteristic of his life, proved his determina- tion to persevere by saying in his Cumbrian dialect, " Yan med deu't " — a text upon which many a good sermon might be preached. One day, it seems, a dis- pute as to the best solution of a problem arose, and a bet was proposed ; but as the stern Quaker preceptor objected to such a proceeding, it was agreed, though one hardly appreciates the moral difference, that the loser should pay for his companion's candles during the winter — probably they were " farthing dips " • — and Dalton won. Another time Mr. Robinson set the boys some stiffish problem, and after a while asked, "Now, John, hast thou done that?" "No," said John, " but yan med deu't." Again, after the lapse of an hour, the same question was asked. " No," he said, " I can't deu't to-neet, but mebby i' th' morn I b2 20 JOHN D ALTON. will"; and, right enough, sleep did the work for him, and the correct answer was forthcoming in the morning. The progress which the boy made under these stimulating influences must have been great, for, in his own words, he " began about twelve to teach the village school, and continued it two years." How he began to teach is thus recorded : — On the outside of his father's cottage, or on the front door, the boy nailed a large sheet of white paper, on which was in- scribed in a bold hand the fact that John Dalton had opened a school for both sexes on reasonable terms, and an additional piece of information indicating that " paper, pens, and ink " — articles then not frequently met with in Eaglesfield — were purchasable within. To begin with, this original school, with a "Prin- cipal " twelve years of age, seems to have been car- ried on in an old barn, then in his father's cottage — much, one would think, to the annoyance of both the weaver and the pupils — and later in the Quakers' Meeting-house ; for these admirable people, unlike some far more powerful sects, see no objection to their " House of God " being used for purposes which have for their aim to make the children of men fitter occupants of the kingdom of heaven. Some strange scenes were witnessed in this school. The boy's pupils were of all ages, from infants to big boys and girls of sixteen or seventeen. The infants sat on the master's knee to learn their "ab — ab." A SCHOOLMASTER TWELVE YEARS OLD. 21 The big boys were often not only crassly ignorant, but some were rough and bad. John Dalton, in the exercise of his authority, desired to chastise these offenders ; but this was sooner said than done. The big boys rebelled against the small " Principal," and — horrihile dictu! — offered to fight him! How the matter ended is a subject upon which history is silent, but we may well imagine that the pluck and Quaker firmness of the young master was equal to coping with the bluster of the ignorant and ill-bred bully. The emoluments coming to the " head " of the school were not large — probably five shillings a week was the maximum — so that we need not wonder at the lad wishing to increase his earnings, or at finding that, after schoolmastering for a couple of years, he turned his hand to the plough and worked as a labourer on a small patch of land which his father farmed. Possibly the fact that his uncle, who was a well-to-do farmer in the neighbourhood, and who had no sons, might make his favourite nephew his heir and successor may have induced Dalton to take to husbandry — an occupation, in those days, quite as honourable and more lucrative than that of a village schoolmaster. He might have remained a " statesman," selling his butter and cows in the neigh- bouring market ; but the forces of nature — whatever that means — were against it, and the boy became a man whose name goes down to posterity as one of the great ones of the earth. 22 JOHN DALTON. Physical work on the farm during the. day gave the boy a zest for intellectual occupations in the evening, vrhen he and his companions sat over the fire breaking their heads about Mr. Robinson's puzzles, and when John worked steadily at the problem until the riddle was solved. Thus, both physically and mentally, his stature grew and developed into a man firm of tissue and of will. When he was fifteen, in 1781, he left his native village for ever. His elder brother had already settled in the county town of Kendal as assistant or usher to a cousin, George Bewley, also a Quaker, who had established a school for " Friends " of both sexes in that town. Brother Jonathan, possibly foreseeing Bewley's speedy retirement, proposed to John to join him with a view to carrying on the school together. So, after the manner of their sect, " Friends " were consulted by the parents on the desirability of this step being taken by their son, and, the oracle having pronounced a favourable judgment, the boy set off for Kendal. His outfit was not a luxurious one. It is said that he first saw an umbrella in a shop in Cockermouth and bought one, thinking, as he afterwards expressed it, that he was becoming a gentleman ; and, with this in one hand and with a bundle of underclothing in the other, John Dalton started for his walk of forty- four miles. His way lay through some of the most beautiful parts of that most lovely of districts, the EAGLESPIELD TO KENDAL. 23 English Lakes. The surroundings of his native village were plain and bleak — true, from the cottage door he could discern the peaks of Skiddaw and Saddleback standing up above the moor ; but that was all. Soon, however, he found himself under Skiddaw's shade, with smooth Bassenthwaite at his feet, and Derwent- water, Avith its bosky islets and fringe of lovely Borrowdale mountains, as a background. The glorious scenery of the lake district must have made a deep impression upon the youth, for ever afterwards, and up almost to his latest day, this was the happy hunting-ground of the man of science. Here, as we shall see in due course, he came almost every summer for many years, and here he made some of his most important meteorological observations, often climbing the dark brow of mighty Helvellyn with his home-made barometers and thermometers, and taking with him bottles to fill with the air from that high altitude, upon the analysis of which he founded more than one of his scientific conclusions. Passing first by Thirlmere, from which in these latter days Manchester draws its supply of the purest of waters, and grazing the edge of Rydal and Gras- mere — since that time the loved retreat of the Lake Poets — he came, past Waterhead, upon Windermere, and leaving this Queen of the Lakes and passing over the fells which divide the watershed, Dalton reached the market town of Kendal. Here he found a com- miinity of some 5,000 souls driving a flourishing 24 JOHN DALTON. trade in homespuns and " Kendal-green " cloth, the packs being taken to Liverpool by hundreds of horses. In those days a stage-coach arrived at Kendal twice a week from London, but the " flying machine " did not carry mails till 1786. At that .time, too, though churches and schoolhouses were being built, the amusements of the people were still of the coarser kind, for public bull-baiting was in full force until 1791, when it was prohibited by order of the Corporation, probably on the instigation of influential members of the Society of Friends, who took then, as they do now, a leading part in all that regards the education and culture of the townsfolk. John served his brother and his friend for four years, and in 1785 Bewley retired, and the brothers Dalton carried on the school, "where youth" of both sexes " will be carefully instructed in English, Latin, Greek, and French; also writing, arithmetic, merchants' accompts, and the mathematics." A photographic copy of the card containing this announcement, from the original in the possession of Mr. George WooUey, of Manchester, has kindly been made for this volume by Mr. Brothers, the well-known photographer. DALTON's KENDAL SCHOOL. 26 JONATHAN and JOHN DALTON, RcrpeCtfuIl;f inform their Friends, and the Public in general, thai they intend to continm the SCHOOL lately t^bt 1>y GEORGE BEWLEY, Where Youth wrill be carefully inftnided in Englifti, Latin, Greek, and French; Also Writing, Arithmetic Merchants Accomprs, And the MATHEMATICS. The School to be opened on the 28th of March, 1785 N. B. Youth boarded in the MaAer's Houfe on reafonable Terms. dalton's card. A second circular sent out in the following year shows that the brothers had enlarged their views on education, and the syllabus forcibly reminds us of that of a technical school of the present day. It is as follows : — " Kendal, July 5th, 1786. " Jonathan and John Dalton take this method of return- ing their acknowledgments to their friends and the public for the encouragement they have received since their opening school ; and, from their care and assiduity in the management of it, manifested in the improvement of the youth under their care, are induced to hope for a continuar 26 JOHN DALTON. tion of their favours. They continue to teach, on reason- able terms, English, Latin, Greek, and French ; also Writing, Mensuration, Projections, Arithmetic, Surveying, Dialling, Merchants' Accounts, G-auging, Optics, Geometry, Algebra, Mechanics, Trigonometry, Fluxions, Pneumatics, Navigation, Conic Sections, Hydrostatics, Geography, Astronomy, Hydraulics, &c. " N.B. — Persons desirous of being instructed in the use of the globes, &c., will be waited upon any time out of school hours. The public may also be informed that they could conveniently teach a considerable number more than at present. Those who send their children may depend upon their being carefully instructed." The Daltons also offered to take in boarders, and their sister Mary came from Eaglesfield to keep house for them, and the parents, now old people, often walked " over fell and slack " a distance of forty-five miles to see th^ir sons. The fee charged was ten and sixpence per quarter; but in 1811 this was raised by Jonathan, who was the head master, with the expressed hope that "a small advance (the increased price of the necessaries of life con- sidered) would not be thought unreasonable." The capital at the disposal of the brothers was not large; indeed, it was so small that on one occasion they had to borrow two or three pounds from Mr. Bewley, and even from their poor parents, to enable them to carry on their enterprise. They took care of A KENDAL SCHOOLMASTER. 27 their money, balanced their books every month, and put down every penny they spent. Mary lent them thirteen shillings and sixpence, and got paid in instalments: "Mary, in part, ,£0 Os. 6d." The first year's income was the largest, and only amounted to XlOO, so the brothers sought to increase their means by collecting rents, and making wills, in order that they might be able to keep their three selves and to preserve a decent appearance. Mrs. Cookson, who was a pupil in the school in 1785, writes to Dr. John Davy (the brother of Sir Humphry, and the discoverer of chlorcarbonyl, or phosgene gas, as he termed it), who lived at the Lakes, the following reminiscences of the school, which contained some sixty boys and girls: "The school was not generally popular, owing to the uncouth manners of the young masters, who did not seem to have had much intercourse with society; but John's natural disposition being gentler, he was more passable. I believe the last time of my going to Mr. Dalton was about the year 1789. He was then become rather more communicative in his manner, but still a man of very few words." John was considered to be very studious. He often made calculations on slips of paper which the girls found torn up and thrown down near his desk. The brothers lived a very secluded life, and Dr. Davy opines, probably with truth, that their manners must have been more than usually hard and ungainly. 28 JOHN DALTON. A letter from another pupil at the Kendal School — a Mr. Isaac Braithwaite, a well-known north-country name — throws further light on Dalton's character and habits. He " recollects the boys being all glad to be taught by John Dalton, because he had a gentler disposition ; and, besides, his mind was so occupied with mathematics that their faults escaped his notice." John Dalton kept school at Kendal for twelve years. During this time he was unceasingly engaged in self-improvement, and some of his methods of doing so . are so different from those adopted at the present day that they deserve a passing notice. At that period one of the few semi-educational periodical publications was the Ladies' and Gentle- men^ s Diary and Woman's Almanac* He had seen some of these numbers when living at Eaglesfield, and had, when thirteen years of age, copied out the whole of the alman,ac for the year 1779. At Kendal he carried out his love for grappling with the problems which these publications contained, many of which involved the knowledge of most of the branches of mathematics then cultivated by English geometers. Prizes were awarded by the publishers of the maga- zine to those who solved the greatest number of questions. In 1787 fifteen such problems were pro- posed, and John Dalton successfully answered thirteen * Edited, it is believed, by Dr. C. Hutton, of the Royal Military Academy. HIS MATHEMATICAL POWERS. 29 and obtained the prize. His replies to the questions of the following year were equally satisfactory, and they showed that he possessed not only high mathe- matical powers, but also that he was able ' to answer general questions on natural science, and had a knowledge of chemistry, and was acquainted with the writings of contemporary French chemists. In 1789 he was awarded the prize of six Ladies' Diaries, and in the G-entlemen's Diary for that year we find the announcement that he had gained the enviable position of first place amongst the correspondents to that journal as having solved a difficult question on hydrostatic equilibrium. But Dalton did not always confine his attention to answering mathematical questions ; sometimes he ventured on ethical ground, and some of his replies, quoted by the late Dr. George Wilson in the Quar- terly Review, are amusing enough to bear repeti- tion. I. — Query hy William Gradidge, of Canterbury. " Whether, to a generous mind, is the conferring or re- ceiving an obligation the greater pleasure ? " — Diary for 1791, p. 32. Answered by Mr. John Dalton, of Kendal. " The pleasure arising from conferring an obligation, es- pecially if it be effected without much inconvenience,* is * Whether this saving clause is intended to be satirical must be left to the judgment of the reader. 30 JOHN D ALTON. pure, and must be a grateful sensation to a generous mind ; but that arising from receiving an obligation is often mixed ■with the unpleasing reflection of inability to remunerate the benefactor. It is pretty clear, therefore, that the pleasure of conferring an obligation must exceed that of receiving one." — Diary for 1792, p. 24. 11. — Query by Mira. " Is it possible for a person of sensibility and virtue, who has once felt the passion of love in the fullest extent that the human heart is capable of receiving it (being by death, or some other circumstance, for ever deprived of the object of its wishes), ever to feel an equal passion for any other object ? " —Diary for 1791, p. 32. Answered by Mr. John Dalton, of Kendal. "It will be generally allowed that in sustaining the disappointments incident to life true fortitiide would guard us from the extremes of insuperable melancholy and stoic insensibility, both being incompatible with your own happiness and the good of mankind. If, there- fore, the passion of love have not acquired too great an ascendency over the reason, we may, I think, conclude that true magnanimity may support the stroke without eventually feeling the mental powers and affections ener- vated and destroyed by it, and consequently that the query may be answered in the affirmative. However, if this passion be too strong, when compared with the other faculties of the mind, it may be feared that the shock will enfeeble it so as to render the exercise of its functions in future much more limited than before." — Diary for 1792, p. 24. In Kendal, as at Eaglesfield, Dalton was singularly fortunate in securing the friendship of persons of similar tastes and character. In this instance it was HIS FRIENDSHIP WITH GOTJGH. 31 to a blind man that young Dalton was indebted for a close and valuable" friendship. The importance which he attached to the assistance in his studies and the aid in forming his habits of investigation which he obtained from blind Gough, Dalton acknowledges in the preface to his Meteorological Observations and Essays published in 1793. "To one person more par- ticularly I am peculiarly indebted, not only in this respect, but in many others ; indeed, if there be any- thing new and of importance to science contained in this work, it is owing, in great part, to my having had the advantage of his instruction and example in philosophical investigation." Dalton explains more fully the character of his friend in the following letter written by him during Mr. Gough's lifetime to Mr. Peter Crosthwaite, of Keswick : — " Kendal, April 12th, 1788. " John Gough is the son of a wealthy tradesman in this town. Unfortunatelj'' he lost his sight by the small- pox when about two years old, since which he has been quite blind, and may now be about thirty. ■ He is, per- haps, one of the most astonishing instances that ever appeared of what genius, united with perseverance and every other subsidiary aid, can accomplish when deprived of what we usually reckon the most valuable sense. He is a perfect master of the Latin, Greek, and French tongues : the two former of which I knew nothing of six years ago, when I first came here from my native place near Cockermouth, but, under his tuition, have since acquired a good knowledge of them. He under- stands well all the different branches of mathematics, and it is wonderful what difficult and abstruse problems 32 JOHN DALTON. he -will solve in Ms own head. There is no branch of natural philosophy but what he is well acquainted with ; he knows by the touch, taste, and smell almost every plant within twenty miles of this place; he can reason with astonishing perspicuity on the construction of the eye, the nature of light and colours, and of optic glasses ; he is a good proficient in astronomy, chemistry, medicine, etc., etc. His father, being very able, has furnished him with every necessary help, and would have sent him to the university had he been inclined. He has the advan- tage of all the books he has a mind for, which others read to him ; he employs one of his brothers or sisters to write for him, or else myself, especially in mathe- matical attempts ; he has never studied the art of writ- ing much, or I doubt not he would succeed. He and I have been for a long time very intimate. As our pur- suits are common — viz., mathematical and philosophical — we find it very agreeable frequently to communicate our sentiments to each other and to converse on those topics." After Gough's death Dalton, in the preface to a second edition of the above-named work, speaks even more freely of his sense of his obligations to his blind friend: — " Mr. Gough might justly be deemed a prodigy in sci- entific attainments, considering the disadvantages under which he laboured. Deprived of sight in infancy (one or two years old) by the small-pox, he was destined to live to an advanced age under this which is commonly reputed one of the greatest misfortunes that can fall to the lot of man. In his case, however, it may fairly be questioned whether he would have had more enjoyment in himself and have been of more use to society in the capacity of a manufacturer, his probable destina- tion, than in that which was allotted to him. By the mathematical education; and, naturally possessing great CHABACTER OF BLIND GOUGH. 33 powers of mind, lie bent them chiefly to the study of the physical and mechanical sciences. There are few branches of science in which he did not either excel or of which he had not a competent knowledge : astronomy, optics, pneimiatics, chemistry, natural history in general, and botany in particular, may be mentioned. For about eight years diiring my residence in Kendal we were in- timately acquainted. Mr. Gough was as much gratified with imparting his stores of science as I was in receiving them. My use to him was chiefly in reading, writing, and making calculations and diagrams, and in participat- ing with him in the pleasure resulting from successful investigations ; but, as Mr. Gough was above receiving any pecuniary recompense, the balance of advantage was greatly in my favour, and I am glad of having this oppor- tunity of acknowledging it. It was he who first set the example of keeping a meteorological journal at Kendal." In subsequent years Dalton made a point of sub- mitting to Gough his own work ; and Gough, espe- cially in the case of Dalton's celebrated investigations on the constitution of mixed gases — about which I shall have more to say hereafter — endeavoured in no very friendly tone to controvert Dalton's results, insinuating that Dalton had made his theory to lit in with his inexact observations ; for " the human mind is naturally partial to its own conceptions, and fre- quently condescends to practise a little self-delusion when obliged by the force of facts and arguments to abandon a favourite notion," and so forth. Dalton, mindful of his former indebtedness to Gough, replies to these somewhat intemperate remarks by simply stating that " in discussions relative to experimental c 34 JOHN DALTON. philosophy we expect facts opposed to facts, and argu- ments to arguments ; whereas in the present instance Mr. Gough has done little more than insinuate that my instruments are inaccurate, and that the results of my experiments are unfaithfully represented, with- out, in any one instance bringing either of these charges home to me." The following letter, written by Dalton from Kendal to his former companion, Alderson, of Eaglesfield, throw;s a further light on his character, and is, therefore,, worthy of being quoted : — "Kendal, 8 mo., 4th, 1788. " Ebspectbd Friend, — Happening a while ago to be in company where the topic of conversation was the deri- vation of surnames, a subject quite new to me, and being, as thou may remember, inquisitive into things seemingly involved in mystery, and which require some sagacity to unravel, I could not help afterwards reflecting a little upon it. The substance of my reflections, and the infor- mation I could get, being put to paper will run nearly as follows. There is very little utility arising from the sub- ject, biit a small matter of curiosity, which I thought might not be altogether unacceptable. " Anciently in this kingdom it seems to have been cus- tomary to have only one name — that is, what is now called the Christian name ; and, that not being sufficient for dis- tinction, others were added to it such as were most fit to answer that end — such as whose son a person was, what trade he was, where he came from, etc. — which, however, were subject to change, according to the caprice of the neighbourhood or fancy of the person, till the Legis- lature found it necessary that they should be fixed, to prevent the evils that might otherwise arise." DALTOK ON SUENAMES. 35 The list of names is too long to be here reproduced ; but it may be well to note that he gives the derivation of his own name as being from Dalton, a village in Lancashire, meaning "Daletown," and also gives that of his correspondent, in concluding the letter, as follows : — " However, as I have explained my own name, I must do the same with thine. Alderson. means undoubtedly 'olderson,' old being pronounced aid in this county, where possibly the name originated ; but it; is not easily made appear how such a name arose. — Please to accept the best respects of thy friend. " John Dalton." Following the lead of Robinson in Eaglesfield, and of Gough in Kendal, Dalton's first attempts at scien- tific investigation were meteorological. The archives of the Literary and Philosophical Society of Man- chester contain two volumes of Dalton's "Meteoro- logical Journal," being the observations made in Kendal from 1787-93 and those made in Manchester 1793-1803, and these daily observations were con- tinued without a break from that time until the evening before his death in 1844. It is interesting to note that the first entry in the journal — that for March 24th, 1787 — was a description of an auroral display which he witnessed — a phenomenon which, as we shall see, afterwards often attracted his special attention. c2 36 JOHN DALTON. In these first beginnings, as in his later scientific work, Dalton used home-made instruments, often crude and inaccurate according to modern notions. " The preceding and following observations on the temperature of the weather were made on instru- ments of my own construction. The barometer is graduated into sixteenths of an inch. The ther- mometer is mercurial, with Fahrenheit's scale, ex- posed to the open air, but free from the sun. The hygroscope is about six yards of whipcord suspended from a nail, with a small weight to stretch it, its scale, tenths of inches, beginning from a certain point — the less the number, the shorter the string and the greater the moisture." In those days re- liable barometers were not as easily obtained as now ; and Dalton not only made such instruments for his own use, but sold them to others. Thus he fur- nished Mr. Crosthwaite, the founder of the Keswick Museum, which still exists, with a barometer and a thermometer, for which he charged him 18s. and 5s. In his letter accompanying the instruments he describes minutely how he made the barometer, and it is clear that he not only did not boil the mercury nor heat the glass tube, but did not even warm both. So that no precautions were taken to remove the adhering moisture and air. This omission Dalton seems to have become aware of, for he writes afterwards as follows : — HOW HE MADE THEKMOMETBKS. 37 " I intend to renew mine as soon as convenient. If thou do the same, be careful in undoing it, and attend to the cautions I give : — Be sure to rub the inside of the tube well with warm dry cotton or wool, and have the mercury, when poured in, at least milk-warm — for moisture is above all things else to be avoided, as it depresses the mercury far more than a particle of air does. Mine is, as I have said, at least j^^th of an inch too low, and yet it is clear of air, and, to all appearances, dry ; but I doubt not but attending to these precautions, whicJi I knew noth- ing of when it was filled, will raise it up to its proper height." Again in January, 1793, he observes : — "I consider both our barometers as inaccurate with respect to the distance of the basins and scales; but this is of little importance provided they be true in other respects. This only serves to show the relative heights of the places to the sea, which we can come at better by other means." How he made his thermometers is described as follows in a letter addressed to Elihu Robinson, his early friend and instructor : — "Kendal, 8 mo., 23rd, 1788. " Deae Cousin, — Herewith thou wilt receive, I hope safely, two thermometers, with somewhat longer scales than the former. Please to take thy choice of the three, to let John Fletcher have next choice, and to reserve the other till my brother comes. " You will probably chuse by the length of the scales ; but those with the least bulbs will soonest come to the temperature of the surrounding medium. However, the largest, I apprehend, will rise or fall to within a degree of the proper place in half an hour in the air. Thou may try whether that thou hast already is with these two or not by dipping the bulbs into a basin of hot water for five minutes. 38 JOHN DALTON. "Possibly the manner of making them may not be unentertaining. A small receptacle being fixed on the end of the tube, a quantity of mercury is poured into it, part of which runs down the tube so as to fill half the bulb. Then a candle is applied to the bulb, which, rarefy- ing the air contained in it, raises the mercury in the tube quickly to the top, and then it escapes in the bubbles through the mercury in the receptacle. This done, it is cooled again, when, the' internal air contracting, another portion of mercury falls down into the bulb; and this operation is repeated till all the air is expelled. Then the mercury is heated above boiling water, and the end of the tube melted and closed at the same time, when, the mercury subsiding, there is left a vacuum. This is done chiefly to keep the moisture, dust, etc., out of the tube. The whole is then put into boiling water, when the barometer stands at thirty inches, and the boiling point thereby determined. Afterwards (if circumstances admit) the freezing point is found by putting it into a mixture of water and pounded ice, or water and snow, which, when melting before the fire, keep at an invariable point (32 deg.) till the whole is melted. If this cannot be done as in summer, it may be set by another thermometer, and the scale adapted accordingly. IST.B. — As the freez- ing points of these two were not found on account of the season, it will not be amiss to try whether they are accu- rate when a convenient season comes. "The principles on which they act need little expli- cation, as mercury, like most other bodies, is subject to be contracted by cold and expanded by heat ; and as the capacity of the bulb remains always filled, the total varia- tion of the mercury in bulk, it is evident, will be mani- fested in the tube.* " The range of the thermometer is little in these parts compared with the more northern. At Petersburgh the summer heat is equal to ours, but in winter severe cold predominates. The thermometer is frequently found 40 or 60 below nothing ; and in Siberia it has been observed * In this oommunioation Dalton takes no account of the expan- sion of the glass bulb. INSTRUMENTS AND. OBSERVATIONS. 39 even 100 or 120 below nothing. On the contrary, in the burning saaids of Africa it reaches 120 or 140 above noth- ing. Is not the internal principle of heat in man and other animals a wonderful phenomenon that can sustain these two extremes without sensible variation ? Eemark. — E^amur's scale (used by the French and others) counts from at the freezing-point to 80 at the boiling-point. Consequently, 2^ degrees Fahrenheit are equal to 1 of Reamur. " ABSTRACT OF MY JOURNAL FOE THE PRESENT YEAR. Thermometer without. Eain. Inches and Decimals. Wet Days. Aurorffi Borealea, Mean. Highest. Lowest. 1 mo. 39 47 20 5-6160 20 6 2 mo. 38-3 47 28 3-3064 23 2 3 mo. 36-8 50 18 2-8183 16 4 4 mo. 46-3 69 32 2-9047 16 11 5 mo. 58-0 80 38 1-1872 10 7 6 mo. 67-3 80 45 2-3137 7 2 7 mo. 56-8 68 47 7-0323 28 1 " THUNDERSTORMS. «6 mo., 19. 2 p.m. distant W. " „ 26. 7 p.m. frequent loud peals, very near. " 7 mo., 3. 6 p.m. frequent peals, some very near. " 8 mo., 16. 7^ p.m. distant about eight miles S.E., but loud and tremendous. About twenty or thirty flashes were observed in as many minutes, and the reports of each heard, though the cloud was but just visible above the horizon ; the zenith clear. — My love to Cousin Euth, self, and family. John Dalton." These barometers were not only used for ascertain- ing the daily or monthly range, but also for measuring the heights of the Lake Mountains, which Dalton first carried out on the hills above Kendal in 1787. 40 JOHN DALTON. The Lake district is not an unfavourable one for measurements of rainfall ; for there the statement that " the rain it raineth every day " is truer than in any other part of the island, nor is its quantity wanting; at Seascale, in Borrowdale, the fall is almost tropical, reaching an average of 160 inches, the mean rainfall for the kingdom being 37'3. Eaglesfield, in days long before girls' high schools or sweet girl graduates were heard of, could evidently boast of young women who took an interest in and were conversant with natural phenomena, for we find Dalton writing to Miss Hudson, an old pupil, a letter in which decimal fractions — a snare and a stumbling-block even to some " great " men of the present day — were made use of. This is worth reading, as showing his method of ascertaining the depth in inches of rain falling at any station from the weight of water collected in the gauge, and as also giving an idea of what a village girl in a remote part of the country was expected to under- stand some more than a century ago. Could the same thing be looked for in a similar district now, in spite of Education Codes and Technical Instruction Acts? "Kendal, 8 mo., 4th, 1788. "Eespected Peiend, — The study of nature having been with me a predominant inclination, it is not likely that I should be ready to prompt others to the same. I have been tempted to think that thou would take a pleas- ure in remarking the quantity of rain that falls with you each day, if thou knew with what facility the same HIS RAIN-GAUGE. 41 is efEeeted. I have observed here that people who are entirely ignorant of the matter suppose it a work of great labour and difficulty, and which can only be done by those they call great scholars. This, however, is a great mistake. A very little knowledge' of mensuration is sufficient for the theory of it, and nothing but plain addition is wanted in the practice. " The annexed scheme will represent the most simple apparatus : — ab is a three-foot stool, to be fixed in a gar- den bed, etc. ; ac and bd two posts fixed in the same about 11 or 12 inches, and support the arm cd, which is 11 inch broad and 1 deep. The pipe of the funnel exactly fits the hole in cd, keeping the fiuinel firm and level. The funnel may be 6, 7, or more inches over ; and if it have an upright rim of an inch it is better, but will do without it. Also, it should be painted, to save it from the weather. A common glass bottle will hold all the water that falls at any time in twenty-four hours, if the funnel be one only six or seven inches diameter — except, perhaps, two or three days in the year. A pair of scales, with a few small weights, are requisite. " Now, to determine the depth of water that falls on any level surface from the above, we have the following tables made for funnels of six and seven inches, wherein are set down the depths, corresponding to the several weights, in decimal fractions. And any person who has learned mensuration will be able to adapt a table to any funnel by knowing that 62^ lbs. avoirdupois equal 1 cubic foot of water. 42 JOHN DALTON. " Suppose there is caught with a funnel of six inches diameter 1 lb. 3 ozs. 6J drs. of water, required the depth : — lb. ozs. drs. = -9778 = -1222 = -0611 = -0153 = -0038 = -0010 1-1812 ' That is, the depth that would on a level surface be 1 inch, 1 tenth, 8 hundreds, 1 thousand, and 2 ten thousand parts of an inch. Weights. Diameters of Funnels. Weights. Diameters of Funnels. lb. av. 6 inches. 7 inches. Av. 6 inches. 7 inches. 1 •9778 •7184 4 drs. •0153 •0112 8 ozs. •4889 •3592 2 •0076 •0056 4 •2445 •1796 1 •0038 •0028 2 •1222 •0898 i •0019 •0014 8 drs. •0306 ■0225 i •0010 •0007 . i •0005 •0004 " Suppose with a funnel of seven inches there is caught 1 oz. 7^ drs. 1 oz. 4 drs. 2 1 ■0449 •0112 •0056 •0028 •0014 •0659 That is, 6 hundredth, 5 ten-hun- ' dredth or thousandth, 9 ten-thousandth part of an inch. " N.B. — The water is supposed to be taken at stated hours, as 6, or 8, or 10 at night. " By this time I apprehend the difficulty generally sup- posed to attend this matter is removed. I should be glad if thou, or any other in your neighbourhood, on whose accuracy one might rely, would find it agreeable and convenient to notice this matter ; but, however, I do not mean to request it, but only to show the easiness with which it's done. Ignorance, no doubt, will look upon this as a trifling and childish amusement, but few of this nature are such in a philosophical sense. If to be able to SYIiLABTJS OF HIS LECTURES. 43 predict the state of the weather with tolerable precision, by which great advantages might accrue to the husband- man, to the mariner, and to mankind in general, be at all an object worthy of pursuit, that person who has in any manner contributed to attain it cannot be said to have lived or to have laboured in vain. — I am, respectfully, thy friend, "John Dalton. " To Sarah Hudson, Eaglesfield." In 1787 Dalton tried his hand at public lecturing, and a course was announced on October 26th of that year in the following terms : — "Oct. 26th, 1787. " Twelve lectures on Natural Philosophy to be read at the school (if a sufficient number of subscribers are procured) by John Dalton. To begin on Tuesday evening, the 13th November next, at six o'cl., and to continue every Tuesday and Thursday at the same hour till compleated. " Subscribers to the whole, half-arguinea ; or one shilling for single nights. " N.B. — Subscribers to the whole course will have the liberty of requiring further explanation of subjects that may not be sufficiently discussed or clearly perceived when under immediate consideration ; also of proposing doubts, objections, etc., all which will be illustrated and obviated at suitable times to be mentioned at the commencement. " A Syllabus of the Lectures. " First and Second — Mechanics. " Introduction. Eules of philosophising on matter and its properties, with the different opinions of the most famous philosophers on this head. "The laws of motion. Mechanic powers. Vibration of pendulums. 44 JOHN DALTON. " Third, Fourth, and Fifth — Optics. " Preliminary discourse. Of the nature and properties of light. Of simple vision. Doctrine of colours. Of re- flected vision. Of mirrors and images reflected from them. Of refracted vision, with the nature of lenses and images exhibited thereby. Of burning glasses. Description of the eye. Manner of vision. Of long and short-sighted eyes. Of spectacles, telescopes, and microscopes. Of the rainbow. " Sixth and Seventh — Pneumatics. "Of the atmosphere. The elasticity of the air. De- scription of the air-pump. The spring and weight of the air proved by a great variety of experiments on the air- pump. Of respiration. Of sound. Of winds. Of the blueness of the sky. Of twilight. "Eighth, Ninth, and Tenth — Astronomy. " Introduction. Of the solar system. Of the figures, magnitudes, distances, motion, etc., of the sun, planets, and comets. Of the progressive motion of light. Of the fixed stars and their phenomena. Of the lunar planets. Of eclipses, tides, etc. " Eleventh and Twelfth — Use of the Globes. " Figure of the earth. Description of the globes. Vari- ous problems performed thereon, amongst which are an explanation of the phenomena of the harvest-moon and the variations of the seasons. Conclusion. " ' Ex rerum causis supremam noscere causam.' " Miss Johns, whose diary will be afterwards re- ferred to, tells us that this very syllabus, and one for 1792, came accidentally in Dalton's way in COLLECTS PLAiTTS AND INSECTS. 45 after-life, when he was looking over some old letters, having been detained in the house by a cold. He burst out into a loud laugh. In the subsequent years of his life at Kendal, Dalton was in the habit of repeating these lectures, both in that town and elsewhere, but with, as it would seem, but scanty success; for in 1791 he found it desirable to lower the admission fee to one-half of what he charged in 1787. Nor is this much to be wondered at; for if, as was the case, the verdict given of his powers as a popular expositor of science in after-years, when he had had more experience and knowledge, was unfavourable (see p. 163), it is reasonable to imagine that only a few out of a mixed audience of Kendal folk of that day would appreciate, hidden under the rough and uncouth demeanour of the lecturer, the true value of the scientific information which he was able to impart. Dalton, at this time, also devoted some attention to Botanical Classification and to collecting the flora of the district. Thus he hoped again to earn an honest penny ; for he writes to Mr. Crosthwaite, of Keswick, that he has dried and pressed a good many plants and pasted them down to sheets of white paper, and found that they look very pretty, and attract the attention of the learned and unlearned, and that a tolerable collection of them, treated in this manner, would be a very proper object for the Keswick Museum; and, he adds, that he 46 JOHN DALTON. thinks he could engage to fill a book of two quires for half a guinea. Whether Mr. Cros- thwaite obtained any sale for these collections is not recorded; but Dalton must have laboured long and pretty successfully in collecting the Kendal flora, as we find that his complete "Herbarium" occupied eleven volumes, of which the title-page of the first, dated 1790, ran : — " Hortus siccus, seu Plantarum diversarum in Agris Kendal vicinis sponte nascentium Specimina, Opera et Studio Johannis Dalton coUecta, et Secundum Classes et Ordines disposita." More than a collector Dalton was not ; for Scientific Botany as we now know it was then non-existent. From collecting the plants of the district, Dalton soon passed on to collecting the commoner insects ; and his butterflies and moths were long to be seen in the Keswick Museum. " Some of these may be thought puerile : but nothing," he writes to Cros- thwaite, " that enjoys animal life, or that vegetates, is beneath the dignity of a naturalist to examine." The desire for knowledge — the strongest motive of his life — induced him to inquire into the limiting conditions of existence amongst the lower animals ; and he made experiments to ascertain how far the vitality of snails, mites, and maggots was destroyed or suspended by immersion in water or by being placed in a vacuum. Next, he began to experiment upon himself — his idea being that quantitative estimations of the food taken LEAVES KENDAL. 47 in, and of the ejecta thrown out by the body, would yield the amount of insensible perspiration. Forty years afterwards he published the numerical results of these experiments. He there states that he had some intention of beginning the study of medicine, " with a view to future practice ; and that on that account, but also partly from my own personal in- terest in knowing the cause of disease and of health, that I was prompted to make such investigations into the animal economy as my circumstances and situation at the time would allow." So far was this wish to take up medicine as a profession at one time a fixed idea in his mind that he consulted many friends on the subject ; but they advised him to give up the project. Elihu Robinson, who fully appreciated his friend's original powers, writes : — "As I have thought thy talents were well adapted to thy present profession, I cannot say thy proposal of changing it was very welcome to me ; believing thou wouldst not only shine, but be really useful in that noble work of teaching youth." As Dr. Henry says, the world has no cause to regret Dalton's decision; for it may be taken for granted that if he had become a country practitioner, his energies would have been thrown into other channels, and science would have lost one of its most original and powerful votaries. A new era for Dalton was now about to open. In 1793 he left Keswick and came to Manchester. CHAPTER II. BAELY YBAES IN MANCHESTBE. As Dalton in 1793 became connected with Man- chester — now a university city — as a teacher in an academy or college in which the higher education was given, it may not be out of place here to remark that several proposals have been made in past times to found a university in this part of the kingdom. So long ago as 1640 Henry Fairfax wrote to his brother Fernandino, the second Lord Fairfax, enclosing a memorial from the public of Manchester praying the Long Parliament to grant a charter to a northern uni- versity, adding, "Posterity may bless you, and the work will speak for itself that the like hath not been in England (if Cambridge be the last) not of two thou- sand years." The Knights of the Shires for Lanca- shire and Cheshire being consulted by Fairfax on the matter, " he found them hopeless of having it. The way to effect it must be by bill, which will be a charge of 100 marks at least (£66 13s. 4d.), and therefore I think it fittest to let that rest, and let none come to solicit it in this troublesome 48 TUTOR IN MANCHESTER ACADEMY. 49 time, when all businesses of the commonweal are at a stay, my Lord of Strafford still keeping us in play." Troublesome times pass over; but these are not the only difficulties which' beset the founding of new institutions ; for when Cromwell had leisure to propose a Member of Parliament for Manchester, and to give ear to the other desires of the town, rival claims sprang up in York; the Wars of the Roses were again waged, this time on educational grounds, the upshot being that Cromwell gave to neither the university which each desired, but by sequestrating the funds of the Dean and Chapter founded the Uni- versity of Durham. In 1789, and again in 1836, similar proposals were made; but the citizens of Manchester had to wait for the accomplishment of their wishes until the Victorian era (1880), when a Royal Charter constituting the Victoria University was granted by Her Majesty. The college in which Dalton became tutor in mathematics and natural philosophy was one estab- lished by the Presbyterians of Manchester as a con- tinuation of the Warrington Academy, with which men such as Priestley, Aikin, Enfield, and Reinhold Forster had been honourably connected. The object of this institution was to give a high-class education, free from every religious or political test, both to laymen, and to candidates for the Presbyterian ministry. Its foundation was a protest against the religious exclusiveness of the English universities at D 50 JOHN DALTON. that date — for then neither to Unitarians, however eminent, like Joseph Priestley, or to Quakers, such as Thomas Young or John Dalton, were the doors of Oxford or of Cambridge open. If Manchester New College had never done anything else — ^and the fact that Martineau is an alumnus of the college is a guarantee that it has done much more — than to give scope to the genius of Dalton, and thus enable him to rise from the drudgery of a village schoolmaster to do his great work for the world, the college would have deserved well of the nation.* It was through Mr. Gough that Dr. Barnes, the principal of the college, heard of Dalton. The post was far from being a lucrative one. The guaranteed salary was £80 for the session, lasting from Sep- tember to June, out of which sum £27 10s. had to be paid to the college for commons and rooms. This left Dalton only with ,£50 a year; but this was a larger sum than he had ever yet had placed at his disposal, and so he remained connected with the Manchester Academy for six years. * The " Academy " remained in Manchester until 1803, when it was removed to York, but in 1840 again returned to its original site in Manchester. In 1889 "Manchester College" was again removed, this time to Oxford, where stately buildings have been erected next to Mansfield College. Over the entrance to the main building stands the inscription, "To Truth ! To Liberty ! To Religion ! " being the words with which a discourse entitled "Free Teaching and Free Learning" was concluded by the first principal of the college. Dr. Thomas Barnes, D.D., in the inaugural address delivered on September 14th, 1786. MANCHESTER A CENTURY AGO. 51 Knowing what Dalton became, the following report of the college trustees for 1797 on his conduct and capabilities is rather amusing: — "In the province of mathematics, natural philosophy, and chemistry, Mr. Dalton has uniformly acquitted himself to the entire satisfaction of the trustees, and has been happy in possessing the respect and attachment of his pupils." In 1794 Dalton had twenty-four pupils in mathe- matics, mechanics, geometry, book-keeping, natural philosophy, and chemistry. He used Lavoisier's "Elements of Chemistry" and Chaptal's "Chemis- try" amongst others. The following letter to Robinson, descriptive of life in Manchester a century ago, is worthy of record : — " Manchester, 2 mo., 20th, 1794. "Dear Cousin, — Amidst an increasing variety of pursuits, amidst the abstruse and multifarious specula- tions resulting from my profession, together with frequent engagements to new friends and acquaintance, shall I find a vacant hour to inform thee where I am and what I am doing ? Yes ; certainly one hour of sixteen some day may be spared for the purpose. " I need not inform thee that Manchester was a large and flourishing place. Our academy is a large and elegant building in the most elegant and retired street * of the place. It consists of a front and two wings ; the first floor of the front is the hall, where most of the business is done ; over it is a library, with about 3,000 vohunes ; over this are two rooms, one of which is mine ; it is about eight yards by six, and above three high, has two windows * Manchester men of the present day will not recognise Mosley Street in this description. d2 52 JOHN DALTON. and a fire-place, is handsomely papered, light, airy, and retired ; whether it is that philosophers like to approach as near to the stars as they can, or that they choose to soar above the vulgar into a purer region of the atmos- phere, I know not ; but my apartment is full ten yards above the surface of the earth. One of the wings is occupied by Dr. Barnes' family ; he is one of the tutors, and superintendent of the seminary ; the other is occupied by a family who manage the boarding, and seventeen in- students with two tutors, each individual having a separate room, etc. Our out-students from the town and neigh- bourhood at present amount to nine, which is as great a number as has been since the institution ; they are of all religious professions ; one Friend's (Quaker) son from the town has entered since I came. The tutors are all Dis- senters. Terms for in-students, 40 guineas per session (10 months) ; out-students, 12 guineas. Two tutors and the in- students all dine, etc., together in a room on purpose. We breakfast on tea at 8^, dine at 1^, drink tea at 5, and sup at 8^ ; we fare as well as it is possible for any one to do. At a small extra expense we can have any friend to dine with us in our respective rooms. My oflB.cial department of tutor only requires my attendance upon students 21 hours in the week ; but I find it often expedient to pre- pare my lectures previously. " There is in this town a large library, furnished with the best books in every art, science, and language, which is open to all gratis ; when thou art apprised of this and such-like circumstances, thou considerest me in my pri- vate apartments, undisturbed, having a good fire, and a philosophical apparatus around me, thou wilt be able to form an opinion whether I spend my time in slothful inactivity of body and mind. The watchword for my re- tiring to rest is 'Past — 12 o'clock — cloudy morning' . . . "There is a considerable body of Friends (Quakers) here ; near 200 attend our first day (Sunday) meetings. I have received particular civility from most of them, and am often at a loss where to drink tea on a first-day after- noon, being pressed on so many hands. One first-day lately I took a walk in company with another to Stock- BECOMES A PRIVATE TEACHER. 53 port; there are but few Friends there, but the most elegant little meeting-house that can be conceived; the walls and ceiling perfectly white; the wainscot, seats, gallery, etc., all white as possible ; the gallery-rail turned off at each end in fine serpentine form ; a white chande- lier ; the floor as smooth as a mahogany table, and covered with a light-red sand ; the house well lighted, and in as neat order as possible ; it stands on a hill ; in short, in a fine sunny day it is too brilliant an object to be attended, by a stranger at least, with the composure required. "John Dalton." In this position of College Tutor Dalton remained, as has been said, for six years, when he resigned his post and devoted himself to the prosecution of scien- tific inquiry, but earning his bread as a private teacher, principally in Mathematics and Natural Philosophy, to such as might come to him, at a charge of two shillings a lesson. In the year 1826, when Dalton had achieved a European renown, M. Pelletier, a well-known Parisian savant, came to Manchester with the ex- press purpose of visiting the illustrious author of the Atomic Theory. Doubtless, he expected to find the philosopher well-known and appreciated by his fellow-citizens — probably occupying an official dwelling in a large national building devoted to the prosecution of science, resembling, possibly, his own College de France or Sorbonne. There he would expect to find the great chemist lecturing to a large and appreciative audience of advanced students. 54 JOHN DALTON. What was the surprise of the Frenchman to find, on his arrival in Cottonopolis, that the whereabouts of Dalton could only be found after diligent search ; and that, when at last he discovered the Manchester philosopher, he found him in a small room of a house in a back street, engaged looking over the shoulders of a small boy who was working his "cyphering" on a slate. "Est-que j'ai I'honneur de m'addresser a M. Dalton?" for he could hardly believe his eyes that this was the chemist of European fame, teach- ing a boy his first four rules. " Yes," said the mat- ter-of-fact Quaker. "Wilt thou sit down whilst I put this lad right about his arithmetic?" On December 15th, 1797, he writes to his brother: " My time .at present is much taken up with tuition at home and in the town together ; so that I can scarcely turn to any particular and mathematical or philo- sophical pursuit ; but of late I have been attending to the philosophy of grammar, and to that of sound." Again, in 1801, he describes his occupations : — "Since the year came in, I have not been much troubled with Vennui. Eight regular pupils by day, and as many more in the evenings, to whom I have sometimes given fifteen lessons a week ; my grammar in the press; the whole of it to write over and to retouch, and to attend to the press ; have required a considerable activity of both body and mind. " Each of his day pupils paid him ten guineas per annum, and the others two shillings a lesson. " I am not yet HIS ENGLISH GRAMMAR. 55 rich enough to retire, notwithstanding," he writes to Elihu Robinson in 1802. Dalton doubtless gave instruction in other subjects than mathematics or physics ; and that his interests were of a wider character we may certainly infer fi'om the fact, to which he refers in the above letter, that he wrote an English Grammar, which was pub- lished in 1801. Dalton greatly admired the writings of Home Tooke; and to Tooke he dedicated his Grammar, and acknowledges in the following fashion his indebtedness to the author of the " Diversions of Purley " : — " To the literary world it will be neces- sary to observe that in this department, Etymology, I have drawn a great deal from one source ; but I have not rested satisfied with the ipse dixit of the 'Diversions of Purley,' when time and opportunity afford me means of confirmation and inquiry." He sent a copy of his Grammar to Home Tooke, as he writes to Jonathan, and then adds : — " But he has got things to attend to now instead of words " — alluding to the fact of the arraignment of Tooke on a charge of high treason. The Grammar appears not to have been devoid of merit; for one thing, he gets rid of "articles " from the parts of speech, and classes them with adjectives as "definitives." His view of "tense " was that of a man of science. " It may be taken as an axiom that all time or duration, in the strict sense of the terms, is either past or future. But for the purposes of 56 JOHN DALTON. speech, -we must have a present time of some dura- tion, which must necessarily be comprised of a por- tion of past and a portion of future — having the present, now or instant, as a boundary between them. Its length may be what we please to make it. Gram- matically speaking, therefore, there are three times — past, present, and future; though, strictly and mathematically speaking, we can admit only two, past and future." He made one rather singular mistake when he states, among the three ways of distinguishing the sexes in English, there is one by change of termination, and gave as examples: " prince — princess, phenomenon — phenomena. " The book does not seem to have enjoyed a very extended sale, although it appears from a letter to his brother, dated 11th of November, 1803, a second edition was called for. On going some years after- wards to the shop of his publisher to ask for a copy of his Grammar, he was told that they had none left. On a more careful search being made, a large parcel of the book was found in a dusty corner, very few having been sold. Dalton himself, however, used to say that some man in Sheffield found it so much to his mind that he published it some years afterwards as his own, with additions. When he arrived in Manchester, Dalton brought with him the manuscript of a volume entitled "Meteorological Observations and Essays," and this was printed and published in 1793, and appeared in METEOROLOGICAL ESSAYS. 57 a second and enlarged edition forty years later. These observations were made and the book written at Kendal. His friends Robinson and Gough had set him the example of carrying out weather obser- vations, and the varying climate of the uplands on which he was born, and the twenty-six years spent amongst the fells and streams of the Lake district, led him insensibly to the study of meteorological phenomena. The splendid appearances of the aurora, more frequently witnessed in that district than in southern England, also stimulated his interest. Indeed, the first entry in his record was that of an aurora seen on March 27th, 1787. " In the evening, " he writes, "soon after sunset, there appeared a re- markable aurora borealis, the sky being generally clear and the moon shining ; it spread over one-half of the hemisphere, appeared very vivid, and had a quick vibrating motion." The volume above referred to contains a long description of auroral phenomena, and an investiga- tion as to their cause. These remarks are character- istic of Dalton's independence, and of the neglect — or contempt, one might even say — with which he treated the views of others — a failing not uncom- mon amongst self-educated but original minds. This independence of spirit and reliance on his own work was clearly expressed by Dalton in the preface to his great work, "The New System of Chemical Philosophy," of which more will be said hereafter. 58 JOHN DALTON. In the preface to the .second part, published in 1810, he says: "Having been in my progress so often misled by taking for granted the results of others, I have determined to write as little as possible but what I can attest by my own experience. " He begins his essay on the aurora as follows : " As this essay contains an original discovery which seems to open out a new field of inquiry in philosophy, or rather, perhaps, to extend the bounds of one that has been as yet just opened, it may not perhaps be unaccept- able to many readers to state briefly the train of circumstances which led the author to the im- portant conclusions contained in the following pages." These conclusions related to the connection between auroral displays and the earth's magnetism, and to the height of the auroral arch above the earth's surface. Before his time the action of the aurora upon the magnetic needle had been pointed out by Wargentin, Celsius, and Halley. The latter supposed the aurora to be caused by magnetism. Dalton, probably ignorant of what had already been done, does not mention the names of previous workers. He decides that the phenomena are closely connected with mag- netism. The very grand aurora of October 13th, 1792, was that which first suggested to him the relation between the phenomena and the earth's magnetism. AXTROEAL OBSEEVATIONS. 59 " When the theodolite was adjusted without doors, and the needle at rest, it was next to impossible not to notice the exactitude with which the needle pointed to the middle of the concentric arches. Soon after the grand dome being formed it was divided so evidently into two similar parts by the plane of the magnetic meridian that the circum- stances seemed extremely improbable to be fortuitous; and a line drawn to the vertex of the dome, being in the direction of tlie ' dipping needle,' it followed, from what had been done before, that the luminous beams at that time were all parallel to the ' dipping needle.' It was easily and readily recollected at the same time that former appear- ances had been similar to the present in this respect, and that the beams to the east and west had always appeared to decline considerably from the perpendicular towards the south, whilst those to the north and south pointed directly upwards. The inference, therefore, was unavoid- able that the beams were guided not by gravity, but by the earth's ' magnetism ' and the disturbance of the needle that had been heretofore observed during the time of an aurora seemed to put the conclusion past doubt. "It was proper, however, to observe whether future appearances corresponded thereto, and this has been found invariably the case, as related in these observations." Then comes Dalton's somewhat daring assump- tion, not, however, borne out by the most recent spectroscopic research : " Now, from the conclusions in the preceding sections, we are under the neces- sity of considering the beams of the aurora borealis of a ferruginous nature, because nothing else is known to be magnetic, and, consequently, that there exists in the higher regions of ' the atmos; phere an elastic fluid partaking of the properties of iron, or rather of magnetic steel." Since Dalton's 60 JOHN DALTON. day science has been provided with the means of de- termining, by help of the spectroscope, the chemical constitution of the atmospheres of the sun and of the far distant fixed stars. Nor has the light from other self-luminous cosmic material, such as nebulae and comets, escaped the analytical power of the prism. The auroral light, too, has also been made to tell its own tale, with the result that a bright green line is always found in its spectrum; and the point of interest to us here is that this line is not found to be coincident with any of the well-known lines in the spectrum of metallic iron. This riddle of the heavens has not yet been properly read. The origin of this green line is, as yet, not ascertained, as it does not belong to any known substance. It is, however, interesting to learn that it is also seen in the spectrum of the Zodiacal light. No point respecting the aurora has been more keenly discussed, nor the results of the discussion been more widely divergent, than that of its height. The estimates vary from feet to thousands of miles. Dalton at first believed the height to be about a hundred miles; but later, in 1834, he describes an auroral arch, of which he calculates the height from a base line drawn from Birmingham to Manchester, to be probably six or eight hundred miles from the earth, " being far beyond the height calculated by Mr. Cavendish of that which was seen at Kimbolton, near Cambridge." ESSAYS ON ATMOSPHERIC PHENOMENA. 61 He adheres to his former opinion on the theory of the display. "I have for the last forty years," he says, "considered both arches and beams to be constituted of magnetic matter, and in ordinary circumstances invisible ; but when a disturbance of the electric fluid takes place in the upper regions these beams, etc., serve to convey the electric fluid from one place to another to restore the equilibrium, which occasions the luminous appearances." In the preface to these Meteorological Essays Dalton says that, in collecting information, he had not "a superabundant assistance from books," but relied on his own observations. This absence of knowledge of the history of his subject, to which reference has already been made, sometimes placed him in difficulties. Thus his theory of the trade winds — viz., that they were caused by the earth's rotation — had long before been explained and pub- lished in the Philosophical Transactions for 1735 by George Hadley. "The inequality of heat," writes Dalton, "in the different climates and places, and the earth's rotation on its axis, appear to me to be the grand and chief causes of winds, both regular and irregular, in comparison with which all the rest are trifling and insignificant." This statement appears to contain "the truth, the whole truth, and nothing but the truth," so far as we now know. For Maury, James Thomson, and other modern authorities admit its validity, whilst 62 JOHN DALTON. the results of other observers — such as those of Dove known as his law of storms — certainly do not conflict with this more general law of atmospheric disturbance. Again, after publishing his conclusions respecting the variation of the barometer, he discovered that he had been forestalled by De Luc. This he duly acknowledged, adding that he considered it to be a favourable circumstance for any theory when it is deduced from a consideration of facts by two persons independently of each other. The essays on the barometer, on the thermom- eter and their variations, on the hygrometer, on the aurora, on rainfall, on the formation of cloud, on evaporation, on the distribution and character of at- mospheric moisture, written, as they were, at the end of last century, might well be considered as remark- able productions from the pen of an experienced philosopher. How much more remarkable must they appear when we remember that they were written by a young Kendal schoolmaster ignorant to a great extent of what had been, written by others, and out of reach of libraries and of books of reference. Perhaps the most pregnant of his conclusions contained in these essays, as leading on to others of still greater consequence, was that on Evapora- tion. After relating his experiments to ascertain for himself the variation of the boiling-point of water with the varying pressiire of the air, he says : dalton's law of vapours. 63 "Upon the consideration of the facts it appears to me that evaporation and the condensation of vapour in the atmosphere are not the effect of chemical affinities, but that aqueous vapour always exists as a fluid sui generis, diffused amongst the rest of the aerial fluids." Moreover, as a cer- tain definite quantity of vapour of water is imbibed by every cubic foot of air, if the temperature be the same, the quantity of moisture which a given bulk of air can take up at a given temperature can be calculated. This observation lies at the root of the law now known as "Dalton's law of vapours " — which is expressed by saying that the same weight of moisture is taken up by a given space, at a given temperature, whether that space be filled with air or be destitute of air. Since Dalton's time, exact experiment has proved that about 2 per cent, more moisture is taken up in vacuo than in the air; but possibly this difference is due to the hygroscopic character of the walls of the chamber, and, if so, Dalton's law is true after all. Although Dalton was not the first to suggest that rain is caused, not by any alteration in atmospheric pressure, but simply and solely by a diminution of temperature, he was the first to render this conclu- sion certain. When moist air is cooled below the dew-point, the aqueous vapour is deposited in the form of drops, which, if very small, remain suspended in the air as cloud, or, if larger, fall as rain. The 64 JOHN DALTON, weight of rain which thus falls is enormous ; if we suppose a cubic mile of air — a minute fraction of the air above any locality — to be saturated at a tem- perature of 95° Fahr., and then that this temperature be reduced to the freezing-point (conditions which constantly happen), no less than 140,000 tons of water will fall as rain. These conclusions of Dalton were of importance. Up to that time it had not been possible to ascer- tain the amount of atmospheric deposit due to a given lowering of temperature ; by following them this could be determined by a simple observation of the dew-point. Dalton 's method of ascertaining this point was very different from that now employed. At the present day the finest and most delicate thermometers are used; the exact temperature at which the dew is deposited is ascertained by the bedimming of a gilt ring or of a silver thimble, the ring or thimble being cooled by the evaporation of ether. Dalton used rough home-made thermometers, and the method of carrying out the experiment was so characteristic of the man, that it can only be fully appreciated in his own words : — " The usual mode of my operations was to find a spring on the side of the mountain and then to take a cup of water from it and pour into a clear dry tumbler glass. If dew was produced immediately on the outside of the glass, the water was returned into the cup, and the glass was again carefully dried outside. During this time the water in the cup was acquiring temperature from the air. HIS METHOD OF EXPEEIMENTATION. 65 It was then returned into the tumbler and held out ex- posed to the current of air. This process was repeated till no dew was found to be formed on the glass. The temperature of the water each time it was put into the tumbler was found by a small pocket thermometer ; and that when it last produced dew on the glass was marked down as the dew-point. At the same time the barometer was noted to iuid the height of the place of observation, and the thermometer to find the temperature of the air ; and the temperature of the springs was an object not wholly devoid of interest. Difficulties, however, some- times occurred. Springs were not always to be found where they were wanted, and many times when found the water was not cold enough to produce dew. In such cases a teaspoonful or two of powdered nitre and sal- ammoniac are thrown into the water and stirred about till dissolved. This generally succeeded. On two or three occasions large snowdrifts were found on the north- east side of the mountain summit, which, being accessible, were particularly useful for the purpose of reducing the temperature of the water, especially as it was easy to carry a quantity of it in a basket and preserve it for a day or more." With regard to another subject which is attracting much attention at present, Dalton's observations are worthy of notice. We now know that all gases, in- cluding probably even hydrogen, by far the most refractory gas, can be liquefied, and even solidified. It is interesting to remember that a prediction to this effect was made by Dalton long before Faraday had published his first experiments on the condensation of the so-called permanent gases in 1821. " There can scarcely be a doubt entertained," he says, "re- specting the reducibility of all elastic fluids of what- ever kind into liquids ; and we ought not to despair E 66 JOHN DALTON. of effecting it in low temperatures, and by strong pressure exerted upon the unmixed gases." Although in all his experiments Dalton made use of rough apparatus — very different from that now necessary for physical or chemical research — it is interesting to find how nearly many of his numerical, results approach those since obtained b}^ much more careful work, and by infinitely more accurate methods and instruments. Moreover, Dalton was fully aware of the existence of the experimental errors which his processes involved. Thus with regard to the modes then adopted for the determination of the hygro- metrical condition of the air, he remarks in 1793 that " to ascertain the exact quantity of water in a given quantity of air is, I presume, an object not yet fully attained." Again in 1799 he determined the point of maximum density of water to be 38° Fahr. Some years afterwards Playfair and Joule corrected this number to 394°. His mode of arriving at results was, however, always ingenious, though often rough; indeed, as Angus Smith says, he seems to have begun his experiments with his hands and finished them off with his head. As an illustration of this, we may quote, in his own words, a description of an experiment made in 1799 to confute Count. Rumford's conclusion that liquids " are perfect non-conductors of heat. " " Took an ale-glass of a conical figure, two and a half inches in diameter and three inches deep; filled it with HIS METHOD OF EXPBEIMENTATION. 67 water that had been standing in the room, and con- sequently of the temperature of the air nearly, put the bulb of the thermometer to the bottom of the glass, the scale being out of the water. Then hav- ing marked the temperature, I put the red-hot tip of the poker half an inch deep in the water, holding it there steadily about half a minute ; and, as soon as it was withdrawn, I dipt the bulb of a sensible thermometer into the water, when it rose in a few seconds to 180°. Time. "TEMPEEATUEE. At Top. Middle. Before the poker was immersed ... 180° ... — 5min. ... 100° ... 60° 20 „ ... 70° ... 60° 1 hour ... 65° ... — Bottom. 47° 47° 47^° 49° 52° " These experiments all evidently agree in proving water to have a proper conducting power, indepen- dent of any internal motion. It surely will not be said that any slight motion unavoidably made at the beginning of an experiment could continue with a powerful effect for upwards of an hour. However, to determine this matter, I made the two following experiments." After describing several, all of which give the same result, he remarks: "We must con- clude, therefore, that the quick circulation of heat E 2 68 JOHN DALTON. in water over a fire, etc., is o^ing principally to the internal motion excited by an alteration of specific gravity; but not solely to that cause, as Count Rum- ford has inferred." On June 27th, 1800, he read an important paper " On the Heat and Cold produced by the Mechanical Condensation and Rarefaction of Air." In this for the first time he measured the amount of heat evolved by compression and heat absorbed by dilata- tion — determinations which, repeated forty years afterwards by Mayer, of Heilbronn, led to what was subsequently proved by Joule to be the true mechanical equivalent of heat. Of this equiva- lency of heat and mechanical energy Dalton had, it appears, no idea, nor was his estimation anything more than a rough approximation; but it was a beginning, and perhaps the reading of this essay may have led Joule to consider the probable exist- ence of such an equivalence, and may have in- duced him to make the experiment on a sounder basis. Five years elapsed before he again communicated a memoir to the Philosophical Society, of which he became secretary in 1800, a vice-president in 1808 (in place of Dr. Roget, who up to that time had resided in Manchester), and president in 1817, an honourable office which he retained until his death in 1844. During this period of apparent rest, Dal- ton 's mind and hands were doubtless busy with HIS PHYSICAL RESEAECHES. 69 preparation for the long series of researches which he gave to the world in the next few years. This, the most prolific period of his life, will be discussed in the following chapters; but before passing to this more serious matter it may be well to learn something about his peculiar eyesight. CHAPTER III. dalton's colour-blindness. The story goes that, desiring to give his mother a birthday present, John Dalton took her a pair of stockings which he saw in a shop window in Kendal, labelled, " Silk, and newest fashion." This would be something fresh for Deborah, who was accustomed to wear her own home-made, knitted, drab-coloured woollen hose. " Thou has bought me a pair of grand hose, John, but what made thee fancy such a bright colour? Why, I can never show myself at meeting in them." Her son, much disconcerted by this exclamation, told her that to his eyes these stockings were of a dark-bluish drab, a very proper sort of go-to-meeting colour. " Why, they're as red as a cherry, John." Neither he nor his brother Jonathan could see anything else than drab in these scarlet stockings, and they both came to the conclusion that the old lady's sight was strangely out of order, until Deborah, having consulted neighbouring wives on this singular difference of opinion, returned with the reply, " Varra fine stuff, but uncommon scarlety." This was the first event which opened John Dalton's 70 dalton's colour-blindness. 71 eyes to the fact that his (and his brother's) vision was not as other men's. It is, indeed, stated that before the year 1793, when he made, as we shall learn, a precise investigation of this peculiarity in his eye- sight, both he and Jonathan tested the vision of their scholars, in several of whom they proved the existence of a similar deficiency in the power of recognising colour. It seems almost incredible that Dalton should have lived to the age of twenty-six without noticing this peculiarity ; and yet it appears less strange when we remember that thousands of persons have, probably since time was, suffered in a similar manner without knowledge of their infirmity; and, indeed, Dalton was almost the first to direct the attention of the scientific world to the subject. The first communication Dalton ever made to the Literary and Philosophical Society of Manchester was a paper read on October 31st, 1794,* entitled, " Extraordinary Facts relating to the Vision of Colours : with Observations by Mr. John Dalton," thus commencing a series of important memoirs to, the Society only ending with his death. In February of that year he wrote a letter to his "dear cousin," Elihu Robinson, describing his own colour sensations, in which he remarks : " I was the other day at a friend's house who is * Dalton was elected a member of the Society on October 3rd, 1794, having been proposed by Dr. Thomas Henry, Dr. Percival, and Robert Owen, the veteran social reformer. 72 JOHN DALTON. a dyer; there was present himself and wife, a physician, and a young woman. His wife brought me a piece of cloth; I said I was there in a coat just of the colour a few weeks before, which I called a reddish snuff colour. They told me they have never seen me in any such coat, for that cloth was one of the finest grass-greens they had seen. I saw nothing like grass about it. They tell me my tablecloth is green, but I say not, and that I never saw a green tablecloth in my life but one, and everybody said it had lost its green colour. In short, my observations have afforded a diversion to all, and something more to philosophers, for they have been puzzled beyond measure, as well as myself, to account for the circumstances. I mean to communicate my observations to the world through the channel of some philosophical society. The young women tell me they will never suffer me to go into the gallery (of the Meeting-house) with a green coat ; and I tell them I have no objection to their going on with me in a crimson (that is, dark drab) gown." Many years after this, when Dalton was about to visit Paris for the purpose of making the acquaint- ance of the French savants — wishing, even as a Quaker, to put in a respectable appearance for the occasion — he went to a tailor's in Manchester (Dalton was at that time a well-known character in that city) and said, " I am going to Paris ; I want thee to sell me some good stout drab cloth," and passing his DALTOK's COLOtJE-BLINDNESS. 73 hand over a piece lying on the counter, he remarked, " I think this will suit ; just the colour I want, and stout good cloth." "Why," said the tailor, "Dr. Dalton, that is a piece of scarlet cloth for hunting- coats ! " to which the Doctor replied, " Ah ! I see thou knowest the infirmity of my eyes." Continuing his investigations, Dalton came across a letter addressed to Priestley, and printed in the Philosophical Transactions for 1777 by Captain Joseph Huddart, containing a description of the ab- normal eyesight of some members of a family named Harris, of Maryport. This description did not satisfy Dalton, and so he writes on " 3rd, 10th month, 1793," to "Respected Friend, Joseph Dickinson," of the above town, requesting him, as an intelligent son of Crispin, to put a series of distinct questions to the sea-captain whose peculiar vision was reported upon by Huddart. The questions were duly put ajid an- swered. Two of the Harrises — " Thos. and the cap- tain thou mentioned — are dead long ago," and there- fore their replies are not forthcoming ; but two other brothers were living, and their eyesight was examined and reported upon, for, singularly enough, as it turned out, four of these brothers Harris were " colour-blind." Yellow was the most conspicuous colour which they saw in the solar spectrum. Roses, pinks, etc., which we call red, appear to them to have some affinity to sky-blue. A tablecloth of Kendal green don't appear like grass ; red sealing-wax appears rather darker ; 74 JOHN DALTON. and there is no difference between dark green and blood. Wishing one of them to choose out a coloured worsted nearest resembling blood, to Crispin's aston- ishment, Harris chose out a dark green. Asked if a white cloth were spotted with blood he could per- ceive it, he said he would not know it from dirt. Asked whether he ever saw blood near slaughter- houses, he replied that he had perceived a wetness, and judged it to' be blood from the little bells of froth frequently upon it, which was all he knew it by. Dalton seems to have been satisfied by this in- formation that the friends Harris's eyes were con- stituted like those of his own and his brother. Replying to Dickinson, he writes : " It is a subject that has not been much handled by philosophers ; I mean, therefore, to make inquii'ies in different places, to ascertain the facts as well as I can, and then endeavour to account for them. The result of my labours will be communicated to the public in some way or other." The friends Harris were, it seems, rather backward in giving their judgment, but Dalton does not wonder at it. " But tell them," he writes, "that formerly, when I used to call pink sky-blue, and incur the ridicule of others, I used to join in the laugh myself, and then nobody thought I was in earnest ; nor did I think at that time that there was such a great difference in the appearance of colour to me and to others as there now seems there is. I thought we differed chiefly in words, and not ideas; dalton's observations. 75 but now I see that I am certain of a real and very- great difference, and I boldly assert with a grave face that pinks and roses are light blue by day and a red- dish yellow by night, that crimson is a bluish dark drab, that all greens (so miscalled) are of a red or blood colour, and the most disagreeable colour imagin- able for a. table — infinitely different from the pleasant verdure of the fields." In a further letter, the Mary- port shoemaker chaffs John on his infirmity very neatly, as follows: — "I find by your accounts you must have very imperfect ideas of the charms which in a great measure constitute beauty in the female sex: I mean that rosy blush of the cheeks which you so much admire for being light blue — I think a com- plexion nearly as exceptional in the fair sex as the sun- burnt Moor's or the sable Etliiopian's, consequently (if real) a fitter object for a show than for a wife." To give the reader an idea of Dalton's scientific style ^- which, like the man, is simple enough, not beating about the bush, but going straight to the point — it may be of interest to quote a few extracts from the Memoir in which he gives his promised investigation of the subject. " EXTKAORDINAKY FaCTS RElATINa TO THE VISION OF COLOURS, ■with 0bsekvati0n8 By Me. John Dalton. " It has been observed that our ideas of colours, sounds, taste, etc., excited by the same object may be very different 76 JOHN DALTON. in themselves without our being aware of it; and that we may, nevertheless, converse intelligibly concerning such objects as if we were certain the impressions made by them on our minds were exactly similar. All, indeed, that is required for this purpose is that the same object should uniformly make the same impression on each mind, and that objects which appear different to one should be equally so to others. It will, however, scarcely be supposed that any two objects which are every day before us should ap- pear hardly distinguishable to one person and very dif- ferent to another without- the circumstance immediately suggesting a difference in their faculties of vision; yet such is the fact, not only with regard to myself, but to many others also, as will appear in the following account. "I was always of opinion — though I might not often mention it — that several colours were injudiciously named. The term piyik, in reference to the flower of that name, seemed proper enough ; but when the term red was substi- tuted for pink I thought it highly improper. It should have been blue, in my apprehension, as pink and blue ap- pear to me very nearly allied, whilst pink and red have scarcely any relation. " In the course of my application to the sciences that of optics necessarily claimed attention, and I became pretty well acquainted with the theory of light and colours before I was apprised of any peculiarity in my vision. I had not, however, attended much to the practical discrimination of colours, owing, in some degree, to what I conceived to be a perplexity in the nomenclature. Since the year 1790 the occasional study of botany obliged me to attend more to colours than before. With respect to colours that were white, yellow, or green, I readily assented to the appropriate term. Blue, purple, pink, and crimson appeared rather less distinguishable, being, according to my idea, all referable to blue. I have often seriously asked a person whether a flower was blue or pink, but was generally considered to be in jest. Notwithstanding this, I was never convinced of a peculiarity in my vision till I accidentally observed the colour of the flower of the Geranium zoncde by candlelight in the autumn of 1792. The flower was pink, but it ap- " OP MY OWN VISION." 77 peared to me almost an exact sky-blue by day ; in candle- light, however, it was astonishingly changed, not having then any blue in it, but being what I called red— a colour which forms a striking contrast to blue. Not then doubt- ing but that the change of colour would be equal to all, I requested some of my friends to observe the phenomenon, when I was surprised to find they all agreed that the colour was not materially different from what it was by daylight except my brother, who saw it in the same light as myself. This observation clearly proved that my vision was not like that of other persons, and, at the same time, that the difference between daylight and candlelight on some colours was indefinitely more perceptible to me than to others. It was nearly two years after that time when I entered upon an investigation of the subject, having pro- cured the assistance of a friend who to his acquaintance with the theory of colours joins a practical knowledge of their names and constitutions. I shall now proceed to state the facts ascertained under the three following heads : — " I. — An account of my own vision. "II. — An account of others whose vision has been found similar to mine. "III. — Observations on the probable cause of our anomalous vision. " I. — Or My Own Vision. " It may be proper to observe that I am short-sighted. Concave glasses of about five inches focus suit me best. I can see distinctly at a proper distance, and am seldom hurt by too much or too little light, nor yet with long application. " My observations began with the spectrum, or coloiired image of the sun, exhibited in a dark room by means of a glass prism. I found that persons in general distinguish six kinds of colour in the solar image — namely, red, orange, yellow, green, blue, and purple. My yellow com- prehends the red, orange, yellow, and green of others ; and 78 JOHN DALTON. my blue and purple coincides with theirs. That part of the image which others call red appears to me little more than a shade, or defect of light ; after that, the orange, yellow, and green seem one colour, which descends pretty uniformly from an intense to a rare yellow, making what I call different shades of yellow. The difference between the green part and the blue part is very striking to my eye : they seem to be strongly contrasted. That between the blue and purple is much less so. The purple appears to be blue much darkened and condensed. In viewing the ilame of a candle by night through the prism the appearances are pretty much the same, except that the red extremity of the image appears more vivid than that of the solar image. " I now proceed to state the results of my observations on the colours of bodies in general, whether natural or artificial, both by daylight and candlelight. I mostly used ribands for the artificial colours. " Bed {by Daylight). " Under this head I include crimson, scarlet, red, and pink. All crimsons appear to me to consist chiefly of dark blue ; biit many of them seem to have a strong tinge of dark brown. I have seen specimens of crimson, claret, and mud which were very nearly alike. Crimson has a grave ap- pearance, being the reverse of every shewy and splendid colour. Woollen yarn dyed crimson or dark blue is the same to me. Pink seems to be composed of nine parts of light blue and one of red, or some colour which has no other effect than to make the light blue appear dull and faded a little. Pink and light blue, therefore, compared together, are to be distinguished no otherwise than as a splendid colour from one that has lost a little of its splen- dour. Besides the pinks, roses, etc., of the gardens, the following British _/?ora appear to me blue — namely, Statice Armeria, Trif olium pratense, Lychnis Flos-cuculi, Lychnis dioica, and many of the Gerania. The colour of a florid complexion appears to me that of a dull, opake, blackish blue upon a white ground. A solution of sulphate of iron in the tincture of galls — that is, dilute black ink — upon dalton's sense of colour. 79 white paper gives a colour resembling that of a florid com- plexion. It has no resemblance of the colour of blood. Bed and scarlet form a genus with me totally different from pink. My idea of red I obtain from vermilion, minium, sealing-wax, wafers, a soldier's uniform, etc. These seem to have no blue whatever in them. Scarlet has a more splendid appearance than red. Blood appears to me red, but it differs much from the articles men- tioned above : it is much more didl, and to me is not unlike that colour called bottle-green. Stockings spotted with blood or with dirt would scarcely be distinguishable. "Bed (by Candlelight). " Red and scarlet appear much more vivid than by day. Crimson loses its blue and becomes yellowish red. Pink is by far the most changed — indeed it forms an excellent contrast to what it is by day. No blue now appears; yellow has taken its place. Pink by candlelight seems to be three parts yellow and one red, or a reddish yellow. The blue, however, is less mixed by day than the yellow by night. Red, and particularly scarlet, is a superb colour by candlelight; but by day some reds are the least shewy imaginable — I should call them dark drabs. " Orange and Yellow (by Daylight and Candlelight). " I do not find that I differ materially from other per- sons in regard to these colours. I have sometimes seen persons hesitate whether a thing was white or yellow by candlelight when to me there was no doubt at all. " Green (by Daylight). " I take my standard idea from grass. This appears to me very different from red. The face of a laurel-leaf (Prunus Lauro-eerasus) is a good match to a stick of red sealing-wax, and the back of the leaf answers to the lighter red of wafers. Hence it will be immediately con- cluded that I see either red or green, or both, different from other people. The fact is, I believe that they both appear different to me from what they do to others. 80 JOHN DALTOK. Green and orange have much affinity ; also apple green is the most pleasing kind. to me ; and any other that has a tinge of yellow appears to advantage. I can distinguish the different vegetable greens one from another as well as most people, and those which are nearly alike or very unlike to others are so to me. A decoction of Bohea tea, a solution of liver of sulphur, ale, etc., etc., which others call brown, appear to me green. G-reen woollen cloth, such as is used to cover tables, appears to me a dull, dark, brownish-red colour. A mixture of two parts mud and one red would come near it. It resembles a red soil just turned up by the plough. When this kind of cloth loses its colour, as people say, and turns yellow, then it appears to me a pleasant green. Very light green paper, silk, etc., is white to me." Then Dalton proceeds to give an account of others whose vision has been similar to his own ; and then summarises his case as follows : — " From a great variety of observations made with many of the above-mentioned persons it does not appear to me that we differ more from one another than persons in general do. We certainly agree in the principal facts which characterise our vision, and which I have at- tempted to point out below. It is but justice to observe here, that several of the resemblances and comparisons mentioned in the preceding part of this paper were sug- gested to me by one or other of the parties, and found to accord with my own ideas. " Chaeactbeistio Facts of Our Vision. "1. In the solar spectrum three colours appear — yellow, blue, and purple. The two former make a con- trast ; the two latter seem to differ more in degree than in kind. "2. Pink appears by daylight to be sky-blue a little faded ; by candlelight it assumes an orange or yellowish appearance, which forms a strong contrast to blue. T-HEOEIES OF COLOUR- VISION. 81 " 3. Crimson appears a muddy blue by day, and crim- son woollen yarn is much the same as dark blue. "4. Red and scarlet have a more vivid and flaming appearance by candlelight than by daylight. " 6. There is not much difference in colour between a stick of red sealing-wax and grass by day. "6. Dark-green woollen cloth seems a muddy red, much darker than grass, and of a very different colour. " 7. The colour of a florid complexion is dusky blue. " 8. Coats, gowns, etc., appear to us frequently to be badly matched with linings, when others say they are not. On the other hand, we should match crimsons with claret or mud ; pinks with light blues ; browns with reds ; and drabs with greens. " 9. In all points where we differ from other persons, the difference is much less by candlelight than by daylight. " It appears, therefore, almost beyond a doubt that one of the humours of my eye, and of the eyes of my fellows, is a coloured medium, probably some modification of blue. I suppose it must be the vitreous humour, otherwise I apprehend it might be discovered by inspection, which has not been done. It is the province of physiologists to explain in what manner the hiimours of the eye may be coloured, and to them I shall leave it, and proceed to show that the hypothesis will explain the facts stated in the conclusion of the second part." The above explanation of his peculiar vision was shown after his death to be erroneous. Mr. Ransome, who made the post-mortem, examined the lenses of Dalton's eyes and found them to be normal to a man of his age. The cause lies much deeper ; and the question whether it is due to a defective condition of the retina, or of the optic nerves, or of the brain substance itself, is still a matter of doubt. The subject has been discussed by Herschel, Young, Brewster, and Helmholtz. Young's suggestions on 82 JOHN DAIiTON. the theory of colour vision, published in the Philo- sophical Transactions of 1802, are perhaps those which have been most generally accepted; and his theory is known as the " three-colour theory." Accord- ing to Young, there are three sets of nerve-fibres in the retina, one of which responds to those vibrations of light which to the normal eye produce the sensation of redness, a second set is sensitive to the green rays, and a third to the violet rays. Thus the first set are excited by the rays of greatest wave-length, the second by those of smaller, and the third by those vibrations of least length of wave. Max Schultze's observations on the minute rods occurring in the retina of birds and reptiles seem to favour this view. For he finds that the anterior extremities of certain of these rods are of a red colour, and are, therefore, capable of absorbing, or are specially sensitive to, the red ray ; whilst others end in a yellow drop, and others, again, end in a colourless one. Helmholtz, a great authority, remarks upon these observations that these rods may with great probability be regarded as the terminal organs of the nerve-fibres, which convey respectively the impressions of red, of green, and of blue light. Another theory of colour-vision has been proposed by Hering, who assumes that there are six fundamental colour sensations — viz. white, black, red, yellow, blue, and green. These six sensations may be divided into three pairs, in each of which the one colour is com- plementary to the other : white to black, red to green. THEORIES OF COLOUR- VISION. 83 and yellow to blue. Three sets of nerves in the retina may be able to distinguish these six colours, because it may be imagined that whilst one colour — say, the red — promotes constructive changes (or changes of assimilation) in the nerve matter, the complementary colour, or, in this instance, the green, promotes de- structive changes (or changes of dissimilation), and that the chemical changes thus effected in the visual substance may give rise to different sensations. The difficulties surrounding the subject are, however, great ; and both the above theories are inadequate to account for either normal or defective colour-vision. We now know that Newton's and Young's ideas as to the threefold nature of coloured light are incorrect. Instead of there being three primary colours, of which all intermediate tints are constituted, and instead of the solar spectrum being made up of three superimposed spectra — red, yellow, and blue, according to Brewster's view — we now know that each ray of a given degree of refrangibility has a definite and distinct wave-length, and that its colour is not the result of the admixture of two or more superimposed rays of different tints. It would thus seem that our power of discerning colour may be dependent upon the retina being able to discriminate each one of the thousands of different-coloured rays to which the eye is sensitive. Dalton's publication of these cases of colour- blindness — a name which we owe to Brewster — drew 1-2 84 JOHN DALTON. general attention to the subject, both at home and abroad. Elie Wartmann, of Lausanne, and Prevost, of Geneva, investigated the peculiarity in question, to which they gave the name of " Daltonism " — a desig- nation which fortunately has not come into general use, as many objections apply to the employment of terms of a personal character to describe natural phenomena, although Dalton himself does not seem to have been annoyed, but rather amused, by this use of his patronymic. The expression " colour-blindness " is also objection- able, because it is not so much blindness as defective vision with which we have to do. George Wilson, whose researches on this question were published in 1855, proposed the name " Chromato-Pseudopsis," or false-colour vision. This is certainly a more correct term, though rather a jaw-breaker. Herschel coined the word " Dichromic," or " two-coloured " vision. But this does not fit the case exactly, because most " colour-blind " eyes can distinguish three col- ours, and, like Dalton, they see differences between red, yellow, and blue ; so that after all the term " colour-blindness " is perhaps the best that has been proposed. As Dalton has stated, the most serious defect in the eyesight of the colour-blind is in the want of normal perception of red and of its complementary colour, green — one side of a laurel leaf appeared to him " a good match for a stick of sealing-wax," and the other "DALTONISM." 86 for a red wafer. He has also pointed out that less confusion exists if the ohjects are seen by artificial rather than by day light. This observation has been explained by Dove, who concluded that we all become sooner blind to red than to other colours, so that the difference between normal vision and that of a colour-blind person is, after all, only one of degree. This fact is borne out by Wilson's experiments. He examined the power of colour- selection — in the case of skeins of coloured wools or pieces of coloured glass — by colour-blind persons, and found that, to begin with, they chose out the scarlet or red skeins correctly, but did so slowly and somewhat hesitatingly ; but that after a while their eyes seemed to become fatigued and they commenced to select wools of a different colour, generally green, and placed these on the red heap, nor was any return to a red skein observed. Whether Dalton's eyes were altogether non-sensitive to the rays of longer wave-length which affect normal sight, as red, is a matter of doubt. He states that the portion of the spectrum which others call red appears to him little more than a shade or defect of light, whilst after that the orange, yellow, and green seem one colour, etc. Thus he excludes red, speaking of it as defective, or more or less black. Herschel, writing to Dalton in 1833, takes the view that he and all others so affected perceive as light every ray which those do who possess normal vision. 86 JOHN DALTON. " The retina," he says, "is excited by every ray which reaches it, nor, so far as I can see, is there the slightest ground for believing that any ray is pre- vented from reaching it by the media of the eye." This, as we know, was contrary to Dalton's notions ; but, as has been explained, Herschel was right so far as Dalton's eye was concerned. George Wilson was the first to draw public attention to the important fact, now generally acknowledged, that this defect of vision is very much more common than was at one time supposed. He concludes that the proportion of persons in this country whose sight is thus defective amounts to one in twenty. The actual number of male persons of all sorts of occupations and positions, tested by Wilson at Edinburgh, was 1,154, and, out of these, one in fifty-five was markedly colour-blind. The extreme importance of ascertaining the existence of this large proportion of persons unable to distinguish between red and green lights at once became evident. The safety of travellers, both by sea and by land, is jeopardised if the conduct of the train or the steering of the ship is in the hands of guards, pointsmen, or sailors whose eyesight is thus defective ; for both at sea and in the railway service red and green lights at night are used — on sea to indicate direction, and on railways to indicate " danger " and " safety " ; by day, too, red and green flags are employed for the same purpose. DANGEES OF DEFECTIVB COLOUK- VISION. 87 So well recognised is this fact, that the various railway boards, the military and naval authorities, and other bodies, both at home and abroad, are now in the habit of testing the eyesight of their employees. The tests used by these various authorities are different; some are known to be satisfactory, others the reverse. In consequence of this uncertainty, a committee of scientific experts was lately appointed by the Royal Society to report upon the most reliable method of ascertaining whether vision is normal or abnormal. The necessity for some improved test was made strikingly evident to the committee, inasmuch as when an official of one of the English railways had explained the method adopted by that company for testing the eyesight of their servants, the Assistant-Secretary of the Royal Society, who is colour-blind, was introduced and tested in the manner in use by the company. The official, having made the tests, and having received what he considered to be satisfactory replies to his questions, remarked that Mr. Rix, the Secre- tary, had good sight, and that he would pass him as normal on an English railway. When informed that Mr. Rix was colour-blind, the official remarked, " I must admit that Mr. Rix being colour-blind is an eye-opener ! " It is also an " eye-opener " to the public to be told that any great railway company test the eyesight of their engine-drivers, guards, and signalmen with such precision that some of them are 00 JOHN DALTON. certainly unable to distinguish between a red " dan- ger " signal and a green " safety " one! The committee recommended that a central authority, such as the Board of Trade, should schedule certain employments in the mercantile marine and on railways, the filling of which by persons whose vision is defective, either for colour or for form, or who are ignorant of the names of colours, would involve danger to life and property. The proper testing, both for colour and form, of all candidates for such posts must be compulsory. The tests for colour ought to be made by competent examiners, and must consist of the selection by the candidate of skeins of coloured wools, according to the method proposed by a Swedish physicist, Holm- gren, now in general use in that country and else- where on the Continent. It further appears, from the evidence given before this committee, that people exist, having normal vision, who are so ignorant, that they are unable to name a red or a green, or even a white, signal when put before them. Such persons are found especially among recruits, who are famous for their stupidity — so much so that they are said some- times not to know how to put the right leg fore- most — and they ought, of course, to be excluded from employments requiring quick and certain observations of colour. It is a well-known fact that excess of tobacco BOAED OP TRADE INQTJIEY. 89 smoking produces a defect in vision called by " the profession " " tobacco amblyopia," similar to that of congenital colour-blindness. John Dalton was fond of his pipe — so much so that in his opinion every philosopher ought to smoke ; and the only fault that he could find in the character of Sir Hum- phry Davy was that he abjured the "weed." It is, however, not to be for a moment supposed that Dalton's evening smoke injured his eyesight; on the contrary, it is clear that his was a case of con- genital colour-blindness. IFor further information on this subject see Captain Abney^s volume on " Colour Vision." Sampson Low & Co., 1895.] CHAPTER IV. DAIiTON'S EARLIER PHYSICAL AND CHEMICAL WORK. Up to the year 1796 we have no evidence that Dal- ton had taken any special interest in chemical re- search, or even had carried on any practical laboratory work. His first introduction to the science, giving him an impetus to its study, seems to have been a course of lectures on chemistry which he attended, given in Manchester by Dr. Garnet. From that time onwards, however, both his mind and his hands were alike constantly occupied in endeavouring to obtain a knowledge of the laws which express the chemical and physical properties of gases. Here it was, he plainly saw, rather than in the case of solids or liquids, that light would come, and to this he bent all the powers of his being. These were sterling honesty of purpose, inflexibility of will, clear-sightedness, and complete devotion to his subject. "If," says he in later life, " I have succeeded better than many who surround me, it has been chiefly — nay, I may say, almost solely — from unwearied assiduity. It is not 90 dalton's mental capacity. 91 so much from any superior genius that one man possesses over another, but more from attention to study, and perseverance in the objects before them, that some men rise to greater eminence than others." And these words are true enough, although per- haps not expressing the whole truth ; for in order to accomplish the greatest things of all something more than mere plodding is wanted. The "Divine Afflatus " must be there, and the scientific imagination must be vivid, if more than a glimpse of Nature's secret ways are to be disclosed. As to how far this power of inspiration was carried in Dalton's case opinions may differ. Some may look upon him only as a slow- witted worker, having but little knowledge or interest beyond the immediate results of his experiments. Others may consider him as one of the great seers of science, dwelling constantly in a realm of thought far beyond the ordinary habitations of mankind, and bringing down for their benefit some of the sweet fruits of a higher world. Probably the truth will be found to lie between these two extremes. All, how- ever, will agree that genius or intellectual insight can accomplish little without perseverance, and that this latter was possessed in high degree by Dalton. Perhaps the most important of Dalton's physical papers is one read on October 2nd, 16th, and 30th, 1801, on the constitution of mixed gases. This con- tains a statement of four important laws which form the basis of our present knowledge. The first of these 92 JOHN DALTOSr. was arrived at from theoretical considerations, the rest by direct experiment. According to the first, the atmospheric oxygen, being heavier than the nitrogen, ought to diminish as the height increased. This is not found to be the case, and Dalton subsequently (1842) modified his first statement, and expressed himself more in accordance with facts as we now know them. The four laws given by him are : — " 1. When two elastic fluids, denoted by A and B, are mixed together, there is no mutual repulsion amongst their particles ; that is, the particles of A do not repel those of B as they do one another. Consequently, the pressure or whole weight upon any one particle arises solely from those of its own kind. " 2. The force of steam from all liquids is the same at equal distances above or below the several temperatures at which they boil in the open air, and that force is the same under any pressure of another elastic fluid as it is in vacuo. Thus the force of aqueous vapour of 212° is equal to 30 inches of mercury ; at 30° below, or 182°, it is of half that force ; and at 40° above, or 252°, it is of double the force ; so,, likewise, the vapour from sulphuric ether, which boils at 102°, then supporting 30 inches of mercury, at 30° below that temperature it has half the force, and at 40° above it, double the force ; and so in other liqiuds. Moreover, the force of aqueous vapour of 60° is nearly equal to i inch of mercury when admitted into a Torri- cellian vacuiun ; and water of the same temperature, con- fined with perfectly dry air, increases the elasticity to just the same amount. " 3. The quantity of any liquid evaporated in the open air is directly as the force of steam from such liquid at its temperature, all other circumstances being the same. " 4. All elastic fluids expand the same quantity by heat ; and this expansion is very nearly in the same equable way EARLY PHYSICAL AND CHEMICAL WORK. 93 as that of mercury ; at least, from 32° to 212°. It seems probable the expansion of each particle of the same fluid, or its sphere of influence, is directly as the quantity of heat combined with it, and consequently the expansion of the fluid as the cube of the temperature reckoned from the point of total privation." Dalton's apparatus was, as has been said, always of the simplest, aud often of the roughest, kind. It may be interesting to see how he determined the tension of aqueous vapour, and ascertained that the vapours of all liquids at equal distances from their respective boiling-points have the same tension. " My method is this : I take a barometer-tube perfectly dry, and fill it with mercury just boiled, marking the place where it is stationary ; then having graduated the tube into inches and tenths by means of a file, I pour a little water (or any other liquid the subject of experiment) into it, so as to moisten the whole inside; after this I again pour in mercury, and, carefully inverting the tube, exclude all air. The barometer by standing some time exhibits a portion of water, etc., of ^ ot ^ of an inch upon the top of the mercurial column ; because being lighter it ascends by the side of the tube, which may now be inclined, and the mercury will rise to the top, manifesting a perfect vacuum from air. I next take a cylindrical glass-tube open at both ends, and of 2 inches diameter and 14 inches in length, to each end of which a cork is adapted, perfo- rated in the middle so as to admit the barometer-tube to be pushed through and to be held fast by them ; the upper cork is fixed two or three inches below the top of the tube, and is ^ cut away so as to admit water, etc., to pass by, its service being merely to keep the tube steady. Things being thus circumstanced, water of any temperature may be poured into the wide tube, and thus made to surround the upper part or vacuum of the barometer, and the effect of temperature in the production of vapour within can be 94 JOHN DALTON. observed from the depression of the mercurial column. In this way I have had water as high as 155° surround- ing the vacuum ; but as the higher temperatures might endanger a glass apparatus, instead of it I used the following : — " Having procured a tin tube of 4 inches in diameter and a foot long, with a circular plate of the same soldered to one end, having a round hole in the centre like the tube of a reflecting telescope, I got another smaller tube of the same length soldered into the larger, so as to be in the axis or centre of it ; the small tube was open at both ends, and on this construction water could be poured into the large vessel to fill it, whilst the central tube was exposed to its temperature. Into this central tube I could insert the upper half of a syphon barometer, and fix it by a cork, the top of the narrow tube also being corked ; thus the effect of any temperature under 212° could be ascertained, the depression of the mercurial column being known by the ascent in the exterior leg of the syphon. The force of vapour from water between 80° and 212° may also be determined by means of an air-pump, and the results exactly agree with those determined as above. Take a Florence flask half -filled with hot water, into which insert the bulb of a thermometer, then cover the whole with a receiver on one of the pump plates and place a barometer gage on the other; the air being slowly exhausted, mark both the thermometer and barometer at the moment ebullition commences, and the height of the barometer gage will denote the force of vapour from water of the observed temperature. This method may also be used for other liquids. It may be proper to observe the various thermometers used in these experi- ments were duly adjusted to a good standard one. "After repeated experiments by all these methods and a careful comparison of the results, I was enabled to digest the following table — the force of steam from water in all the temperatures from 32° to 212°." In the fourth essay of this series Dalton discusses another most important physical property of gases LAWS OF EXPANSION OF GASES. 95 and vapours, or, as he terms them, " elastic fluids " — viz., their expansion by heat. He first quotes the discordant results obtained by Berthollet and Monge, according to which the expansion of one gas differed widely from that of another. "These conclusions were so extremely discordant with and even con- tradictory to those of others that I could not but suspect some great fallacy in them, and found it in reality to be the fact. I have no doubt it arose from the want of due care to keep the apparatus and materials free from moisture." Dalton next proceeds to describe the methods he adopted in order to exclude this and other sources of error from his experiments, and then gives his conclusions in the following remarkable words : — " The results of several experiments made upon hydro- genous gas, oxygenous gas, carbonic acid gas, and nitrous gas — which were all the kinds I tried — agreed with those on common air, not only in the total expansion, but in the gradual diminution of it in ascending. . , . Upon the whole, therefore, I see no sufficient reason why we may not conclude that all elastic fluids tmder the same pressure expand equally by heat, and that for any given expansion of mercury the corresponding expansion of air is proportionally something less the higher the tem- perature. This remarkable fact that all elastic fluids expand the same quantity in the same circumstances plainly shews that the expansion depends solely upon heat, whereas the expansion in solid and liquid bodies seems to depend upon an adjustment of the two opposite forces of heat and chemical affinity : the one a constant force in the same temperature, the other a variable one according to the nature of the body — hence the unequal 96 JOHN DALTON. expansion of such bodies. It seems, therefore, that gen- eral laws respecting the absolute quantity and nature of heat are more likely to be derived from elastic fluids than from other substances." This law of equal expansion of all gases for equal in- crements of temperature has been generally known on the Continent as " Gay-Lussac's " or " Charles's law," but ought to be called " Dalton's law of expansion," as he first announced it and gave experimental evidence of its truth, and the claims of the Manchester philoso- pher are generally now allowed. In 1804, however, these questions were under discussion, and he writes : " My lately published essays on gases, etc., together with the more recent ones read at our society, and of which I gave the result in my late lectures, have drawn the attention of most of the philosophers of Europe. They are busy with them at London, Edinburgh, Paris, and in various parts of Germany, some maintaining one side and some another. The truth will surely out at last." In following the progress which Dalton's mind makes towards the most fruitful of his ideas — that of the Atomic Theory of chemistry — it is interesting to note that at the end of this essay he gives a diagram to illustrate his conception of the constitution of the atmosphere. He gives to the particles of the different gases contained in the air separate signs, and so arranges these signs or marks — the space for each gas being equal — that the marks indicate the real COMPOSITION OF ATMOSPHERIC AIR. 97 densities of the gases in question. This sho\/s that his mind was occupied with the atomic conception that gases are composed of definite particles. Thus he states "that homogeneous elastic fluids are con- stituted of particles that repel one another with a force decreasing as the distance of their centres from each other." " There is, therefore, not any doubt," as Dr. Henry says, "that it was in contemplating the essential "condition of elastic fluidity that he first distinctly pictured to himself the existence of atoms." The next important research is an " Experimental Enquiry into the Proportion of the Several Gases or Elastic Fluids constituting the Atmosphere," read November 12th, 1802. This is interesting, in the first place as giving the result of his analyses of the air in Manchester near the sea's level and also at the summit of Helvellyn — the results showing no perceptible difference in the composition of the air taken from these two sources — a difference which, according to his views as already stated, ought to exist owing to the difference in specific gravity of oxygen and nitrogen, although this expected varia- tion could scarcely be observed by his methods of analysis. In spite of his rough methods, Dalton here, as elsewhere, obtained results the correctness of which has been borne out by later work. Especially is this the case with the question of the constant composition G 98 JOHN DALTON. of the atmosphere as regards oxygen and nitrogen. Thus he finds that " the bulk of any given quantity of atmospheric air appears to be reduced nearly 21 per cent, by abstracting its oxygen " — a statement, be it observed, which holds good to-day. Then he continues : " This fact, indeed, has not been generally admitted till lately" (doubtless referring to Caven- dish's previous determinations, in which it was shown that the air of London — Marlborough Street — and the country — Kensington — had the same compo- sition, containing on an average 20-83 per cent, of oxygen), " some chemists having found, as they appre- hended, a great difference in the quantity of oxygen in the air at different times and places ; on some oc- casions 20 per cent., and on others 30 and more, of ox5'gen are said to have been found." " This, I have no doubt," Dalton wisely and truly adds, " was owing to their not understanding the nature of the operation and of the circumstances influencing it. Indeed, it is difficult to see, on any hypothesis, how a dis- proportion of these two elements should ever subsist in the atmosphere." Subsequent more exact determinations have shown that certain small variations do, in fact, exist, but that any permanent diminution in the percentage of oxygen at high elevations is not traceable, doubt- less owing to the atmospheric disturbances, and also to the fact — also discovered by Dalton — that gases act as vacua to one another. dalton's "nitkous and nitric acids." 99 Another and still more interesting result was arrived at by Dalton in the course of these experi- ments, and shows the direction in which his ideas were moving. In his air-analyses he used the well- known method of mixing the air with nitrous gas (our nitric oxide) when the oxygen is absorbed with formation of soluble red fumes due to the union of the atmospheric oxygen with nitrous gas. This process, he remarks, has been much discredited by late authors ; but he considers it to be not only the most elegant and expeditious of all, but also as correct as any of the others. Now comes the interesting obser- vation — the first germ of his great discovery of the law of chemical combination in multiple proportions. He finds that if 100 measures of common air be put to 36 of pure nitrous gas in a tube -f^ of an inch wide and 5 inches long, after a few minutes the whole will be reduced to 79 or 80 measures and exhibit no signs of either oxygenous or nitrous gas. If, on the other hand, 100 measures of common air be admitted to 72 of nitrous gas in a wide vessel over water, such as to form a thin stratum of air, and an immediate momentary agitation be used, then there will, as before, be found 79 or 80 measures of pure azotic gas (nitrogen) for a residiium. But if in the last experiment less than 72 measures of nitrous gas be used, there will be a residuum containing oxyge- nous gas ; if more, then some residuary nitrous gas will be found. Now for Dalton's explanation, g2 100 JOHN DALTON. which, as I have said, is the first inkling of his great law according to which chemical combination proceeds. "These facts," says Dalton, "clearly point out the theory of the process. The elements of oxygen may combine with a certain portion of nitrous gas, or with twice that portion, but with no intermediate quantity. In the former case nitric acid is the result, in the latter nitfous acid ; but as both these may be formed at the same time, one part of the oxygen going to one of nitrous gas, and another to two, the quantity of nitrous gas absorbed should be variable — from 36 to 72 per cent, for common air. This is the principal cause of that diversity which has so much appeared in the results of chemists on this subject. In fact . . . the wider the tube or vessel the mixture is made in, the quicker the combi- nation is effected; and the more exposed to water, the greater is the quantity of nitrous acid and the less of nitric that is formed." * Soon after the publication of the last paper Dal- ton read one upon the Tendency of Elastic Fluids to Diffusion. Everybody knows that oil and water do not mix, so also if spirits of wine is gently poured on to the top of water the film of lighter spirit remains floating on the water, although if the two * This was written before November, 1802, but not printed till November, 1805. The first edition of the "New System of Chemi- cal Philosophy " is dated May, 1808. DIFFUSION OF GASES. 101 be stirred perfect mixture occurs, Priestley having already noticed that when gases which do not act chemically upon one another, but are of different specific gravities, like spirits and water, are once mixed they do not again separate ; but he thought that just as spirits and water, when carefully brought together, remain distinct, so two gases of different densities might also remain in layers one above the other. This question was the one which Dalton wished to answer ; or, as he puts it. Can a lighter elastic fluid (gas) rest upon a heavier one? and he proved by a very simple experiment that it cannot do so. The only apparatus found necessary was a few phials and tubes with perforated corks ; the tube mostly used was one 10 inches long and of ^^ inch bore ; in some cases a tube 30 inches in length and J inch bore was used; the phials held the gases that were the subject of the experiment, and the tube formed the connection. Dalton substituted in many experiments a long "church- warden " clay pipe for the glass tube. " In all cases, the heavier gas was in the under phial, and the two were placed in a perpendicular position, and suffered to remain so during the experiment in a state of rest; thus circumstanced, it is evident that the effect of agitation was sufficiently guarded against ; for a tube almost capillary and 10 inches long could not be instrumental in propagating an admixture 102 JOHN D ALTON. from a momentary commotion at the commencement of each experiment." The gases experimented on were atmospheric air, oxygen, hydrogen, nitrogen, nitrous oxide, and carbonic acid. After the gases had remained in contact as described for a given length of time, the composition of the gas in each phial was determined, and the analysis invariably showed that a passage of the heavier gas upwards and the lighter gas downwards had occurred; or, in other words, gases diffuse mutually into each other. We had to wait for a knowledge of the laws of gaseous diffusion for upwards of thirty years, for it was not until 1834 that Graham discovered that the rate of diffusion of a gas is inversely proportional to the square root of its density. Thus a given volume of oxygen, which is sixteen times as heavy as hydrogen, takes four times as long to diffuse as the same volume of hydrogen. Many years had again to elapse before the true significance of Graham's law was understood. In 1848 Joule proved the correctness of Bernouilli's views that the pressure of the air could be explained by the impact of its particles on the walls of the containing vessel, and he calculated the mean velocity which the molecules of the gas — these being con- stantly in motion — must possess in order to effect the observed pressure. Dalton's words, which follow, come very close to the modern explanation : — D Alton's law of partial prbssukes. 103 "1. The diffusion of gases through each other is effected by means of the repulsion belonging to the homogeneous particles, or to that principle which is always energetic to produce the dilatation of the gas. " 2. When any two or more mixed gases acquire an equilibrium, the elastic energy of each against the surface of the vessel, or of any liquid, is precisely the same as if it were the only gas present occupying the whole space, and all the rest were withdrawn." Clausius, Maxwell, and other physicists, have ex- tended and completed the dynamical theory of gases, and applying to these molecules the well-known laws of masses in motion, the laws of gases, as found by experiment — viz. Boyle's law of pressures, Dalton's law of expansion, Graham's law of diffusion, and what is usually known as " Avogadro's theory " (to which reference will again be made) — all find their theo- retical explanation, and have for their existence a sound physical foundation. The phenomena of the solubility of gases in water next attracted Dalton's attention, especially as regards the solubility of the gases under variation of pressure. We all know that when water is saturated with gas under pressure, as in soda-water, and when the press- ure is removed, the gas escapes with effervescence. The question as to the relation between amount of gas and pressure had been made the subject of 104 JOHN DALTON. experiment. Dalton's old friend, Dr. William Henry, had already communicated to the Royal Society the re- sults of his experiments on the same subject, express- ing what is now known as " Henry's law " — viz. that the amount of gas absorbed by water varies directly as the pressure. Dalton asked himself, What will happen if a mixt- ure of two gases, such as oxygen and nitrogen, is shaken up with water ? On making the experiment he found that the quantity of each gas absorbed is in- dependent of the other — that is, supposing the mixt^ ure to be one-half oxygen and one-half nitrogen, the amount of oxygen dissolved is exactly half what it would have been if the space occupied by the nitrogen had been a vacuum ; and in the same way exactly half as much nitrogen is absorbed as would have been the case had the space occupied by the oxygen been vacuous. This is known as " Dalton's Law of Partial Pressures," and both Henry's and Dalton's laws have stood the test of time. Dalton's views as to how the gas is dissolved in the water are interesting, because they shadow forth his coming Atomic Theory. His mind was, as has been said, of a corpuscular turn. Having this habit of mind, he conceived the particles of gas amongst those of water; "the former retained their elasticity or repulsive power amongst their own particles, just the same in the water as out of it, the water having no other influence in this respect than a ABSORPTION OF GASES BY WATER. 106 mere vacuum, and no other gas with which the first one is mixed having any permanent influence in this respect." He believed that the different gases which do not combine chemically with the water are ab- sorbed in certain definite fractions of the bulk of the water, in amount corresponding to the cubes of the reciprocals of the natural numbers — 1, 2, 3, etc., or ,U 4 i and so on-the same gas always being in the same proportion, provided the temperature and pressure remain constant. He looked upon the phenomenon as a purely mechanical one, the particles of the gas taking a certain position amongst those of the water; just as we may imagine grains of sand strewed regularly amongst a quantity of small shot. Dalton gives pictures of this arrangement — "a hori- zontal view of air in water" and "a profile view of air in water " — with marks where the particles of the different gases are supposed to lie. It is scarcely necessary to remark that this mere mechanical view of the matter will not hold water. We now know that the question has to be looked at in a totally different light, that Dalton's idea of definite fractions is altogether erroneous, and that every gas possesses a fixed co-efficient of solubility, which is constant for every given temperature, and which cannot be ascer- tained by calculation, but must be determined by experiment. In other words, we do not yet know the law regulating solubility and temperature, nor 106 JOHN DALTON. can we explain why one gas is more soluble than another. But although Dalton's theory of solubility was altogether mistaken, it was one of the most fruitful theories ever devised, because it led him to the greatest of all his discoveries — namely, to the deter- mination "of the relative weights of the ultimate par- ticles of gaseous and other bodies." How exactly this came about, and why the numbers which he puts down in this first published table of atomic weights were pushed in, as it were, neck and crop at the end of this essay on the solubility of gases, will always remain a mystery. It must suffice us that there it stands on page 287 of the first volume of the new series of the "Memoirs of the Literary and Philo- sophical Society of Manchester" — having been read on October 21st, 1803, but published in November, 1805 — as the great foundation-stone in chemical science; for upon it and what naturally followed it all the edifice of modern chemistry rests. This is the form in which it first saw light: — TABLE Of the Relative Weights of Ultimate Particles OF Gaseous and Other Bodies. Phosphorus 7-2 Phosphuretted hydrogen 8-2 Nitrous gas 9-3 Ether 9-6 Gaseous oxide of carbone 9-8 Nitrous oxide 13-7 Hydrogen Azot ... 1 ••• 4-2 Carbone ■•• 4-3 Ammonia •■• 5-2 Oxygen Water ■•• 5-5 ••• 6-5 RELATIVE WEIGHTS OP ULTIMATE PARTICLES. 107 TABLE OP THE RELATIVE WEIGHTS OF ULTIMATE PARTI- CLES OP GASEOUS AND OTHER BODIES — (continued). Sulpliur 14-4 Nitric acid 15-2 Sulphuretted hydrogen 15-4 Carbonic acid 15-3 Alcohol 15-1 Sulphureous acid ... 19-9 Sulphuric acid 25-4 Carburetted hydrogen from stag, water ... 6-3 defiant gas 6-3 The only explanation which Dalton vouchsafed is given in the following words : — " The greatest difficulty attending the mechanical hypothesis arises from different gases observing differ- ent laws. Why does water not admit its bulk of every kind of gas alike ? This question I have duly con- sidered, and, though I am not able to satisfy myself completely, I am nearly persuaded that the circum- stance depends upon the weight and number of the ultimate particles of the several gases — those whose particles are lightest and single being least absorbable, and the others more, according as they increase in weight and complexity.* An inquiry into the relative weights of the ultimate particles of bodies is a subject, as far as I know, entirely new ; I have lately been prosecuting this inquiry with remarkable success. The principle cannot be entered upon in this paper ; but I shall jiist subjoin the results as far as they appear to be ascertained by my experiments." It is, therefore, clear that it was by experiment and not by mere reasoning that Dalton obtained the * " Subsequent experience renders this conjecture less probable." 108 JOHN DALTON. above numbers. What the exact nature of these experiments was it is not easy to infer, as he does not explain how he arrived at them. They were probably in part his own, but also, and to a considerable extent, those of other chemists, whose results Dalton made use of in calculating his numbers. We shall have to return to this subject when discussing the Atomic Theory. CHAPTER V. dalton's daily life. Dalton's daily wants were of the simplest, and his habits most uniform. When he left the College he lived for a time in a house in Faulkner Street, and worked in rooms placed at his disposal as laboratory and study in the house of the Literary and Philo- sophical Society, then, as now, situated at 36, George Street, Manchester. Not long afterwards he removed to the house of John Cockbain, a member of the Society of Fiiends. After residing with him for some time, Dalton in 1805 went to live in the house of a friend, the Rev. William Johns, in Faulkner Street — a street long since entirely given up to warehouses and offices — hard by, and there he continued to reside until the year 1830, when Mr. Johns left, and Dalton took a house and lived alone. How this residence with the Johns family came about is thus related by Miss Johns, the daughter. " As my mother was standing at her parlour window, one evening towards dusk, she saw Dr. Dalton passing on the other side of the street, and, on her opening the window, he crossed over and greeted her. ' Mr. Dalton,' said she, ' how is it that you so seldom come 109 110 JOHN D ALTON. to see US ? ' ' Why, I don't know,' said he ; ' but I have a mind to come and live with you.' My mother thought at first that he was in jest ; but finding that he really meant what he said, she asked him to call again the next day, after she should have con- sulted my father. Accordingly he came and took possession of the only bedroom at liberty, which he continued to occupy for nearly thirty years. And here I may mention, to the honour of both, that throughout that long connection he and my father never on any occasion exchanged one angry word, and never ceased to feel for each other those sentiments of friendly interest which, on the decline into years of both, ripened into still warmer feelings of respect and affection." The following graphic description of his life in Man- chester was given by his lifelong friend. Miss Johns, who had ample opportunity of becoming acquainted with Dalton's moral qualities and domestic tastes: — " The doctor's habits of life," she writes, " were so uni- form and unvaried as to be soon related. On Sundays he always dressed himself with the most scrupulous attention to neatness, attended public worship twice — except when indisposed, or on very particular occasions, which, how- ever, the writer does not remember to have occurred a dozen times in all — dined, during his life, with his friend Mr. Thomas Hoyle, the printer of Mayfield, and, returning ' home to tea, spent the evening in his philosophical pur- suits. His dress was that usually worn by the Quakers, avoiding, however, the extreme of formality and always of the finest texture; hat, gloves, gaiters, and even a handsome cane to correspond. In his general intercourse, HIS DAILY LIFE. Ill also, he never adopted their peculiar phraseology. With respect to his religious principles, I should be disposed to think that he had never made theology, properly so called, a study. He certainly never mentioned having done so ; but his reverence for the great Author of all things was deep and sincere, as also for the Scriptures, in which His revealed will is expressed. When the occasion called for it, I have heard him express his sense of the duty and propriety of the religious observance of Sunday, and also his serious disapprobation of its violation. Although frequently solicited, he refused all invitations to dine out on that day, except a very few times at Dr. Henry's, and once or twice elsewhere, when, as he observed to me, he was asked to meet a very distinguished professor whom he shoTild otherwise have missed the opportunity of seeing. But when the same friend, presuming on his former compliance, again invited him on that day he received a refusal, which prevented any further appli' cation. His week-days — every day, and all day long — were spent in his laboratory, with the exception of Thursday afternoons, when he accompanied a party of friends about three miles into the country to bowl, and entered into the amusement with a zest infinitely amus- ing to all who were present. He also spent a few minutes, generally between light and dark, at the Portico, in reading the daily papers. He rose about eight in the morning, always lighted his laboratory fire before breakfast, after which meal he finished, his toilet and repaired to his laboratory, which he seldom left until dinner. He dined at one, but always came in in much haste when dinner was partly over — I suppose to save time. He ate moderately, and drank only water. He was obliged to eat slowly on account of the conformation of his throat, which was very narrow. After dinner he always spent about a quarter, rarely half an hour, in chatting with the different members of the family, or any visitor, or in looking over any chance publication lying on the table. After spending the after- noon in his laboratory, he drank tea at five, rarely coming in until the family had nearly finished. He was very methodical in the quantity he took at meals. After tea, 112 JOHN DALTON. to his laboratory again, where he staid until nine (supper- time), when he regularly shut up for the night, ate a light supper, generally of meat and potatoes, until about his sixtieth year, when he changed this for meal porridge, with milk or treacle, or occasionally a couple of eggs. After supper we all sat together, and generally had a nice chat, for which the labours of the day had excellently prepared us all ; and I will venture to say that few fire- sides have ever presented a scene of more innocent and pleasant recreation than did ours during these the busy years of our life. The doctor took little part in the conversation, though he shewed that he listened by fre- quently smiling, and now and then uttering some dry, laconic witticism in reference to what was passing. He and my father smoked their pipes unremittingly. Not unfrequently we were joined by two or three political friends, who talked over the news of the times, etc. The doctor enjoyed their society, but took little part in the conversation, in politics none whatever, nor for years had we any idea what his views on the subject were (Conserv- ative). Occasionally he took the chief part in conversa- tion ; but this only when we were quite alone, or when Mr. Ewart stepped in, as he sometimes did. He and the doctor had a great esteem for each other, which lasted through life. When, however, this gentleman was our visitor, the evening seldom ended without my father and he getting deeply into metaphysics — a favourite study with both. The doctor generally listened intently, but, from an occasional ironical smile, I used to suspect that he thought it mostly 'vain wisdom all and false philoso- phy.' My sister Catherine's wit and animated nonsense were, I fancy, more to his taste. When we had no com- pany we always withdrew before eleven, when the doctor pursued his meditations for nearly an hour longer, and then, having perambulated the lower part of the house to see that all the fires were out, he himself went to bed, and by midnight all were at rest." That he was able not only to make 200,000 me- teorological observations, but to accomplisli so much WORK AND PLAY. 113 more, depended to a great extent on his methodical habits. His life went as by clockwork. A lady, who lived nearly opposite his laboratory in George Street, used to say that she knew the time to a minute by seeing Dr. Dalton open his window to read off the height of his thermometers. His observance of method and his punctuality were noticeable in all his doings. For many years President of the Literary and Philosophical Society, he was punctilious as to the commencement of the business of the meet- ing at seven, and even more so as to its termination at nine. One of his intimates was Peter Clare, one of the secretaries of the Society, and a clockmaker by trade. At Dalton's request, Peter presented to the Society one of his best clocks (it now stands in the meeting-room), which only sounds one stroke on the bell during the twenty-four hours, and that stroke is at nine o'clock in the evening ; thus notice was given that the meeting must conclude. Not only in his work, but in his recreations, the same method prevailed. His summer holidays were usually spent at the English Lakes, where, as we shall see, he occupied himself always in the same way. When living in Manchester his only relaxation from the round of daily work was on Thursday after- noon, which he regularly devoted to a game of bowls on the green of the " Dog and Partridge " — then in the country, but now closed in by grimy streets. He there appears to have enjoyed himself with some H 114 JOHN DALTON. chosen spirits, watching the bowls as they roll with the anxiety of the confirmed player, and showing, as Angus Smith remarks, a glimmer of the latent en- thusiasm of his mind by swaying his body, indicating the course which he wished his bowl to take, as if endeavouring to influence it. Methodically, he played only a certain fixed number of games, got his tea at the inn, smoked his " churchwarden " in the com- pany of his fellow-players, and went " home " to his laboratory — for this was, in truth, his home far more than his rooms in the neighbouring house, where he consumed the victuals needed to supply the metabolism of the body, and where he slept in order to obtain further nerve-power for next day's brain- work. He used to say that he went to the "Dog and Partridge " on Thursdays because he preferred his Saturday half-holiday in the middle of the week. He took no part, and probably little interest, in the political or even in the social questions of the hour. It is true that he went every day for a few minutes to the Portico Library near his laboratory to read the papers, but not even to his intimate associates — he can scarcely be said to have had intimate friends — did he speak either on religion or on politics; indeed, the Johns family did not know that he was a Conservative, and some thought that he was a Liberal; so we may put him down as Liberal-Conservative, which perhaps may be defined as a man who thinks EXCURSIONS IN LAKE-LAND. 115 things ought to progress, but would rather they re- mained as they are. In a paper read in 1821 on " The Dew-Point, etc., from Observations made in the North of England," Dalton says : " As I had for some years been in the habit of allowing myself a week or two in summer for relaxation from professional engagements, and had generally s-pent the time in the salubrious air of the mountains and lakes near my native place in the North of England, it was, therefore, an addi- tional gratification to be enabled to unite instruction with amusement. I began my observations in 1803, and have continued them almost in every successive year to the present." Helvellyn was the mountain he most frequently ascended, having been on its summit forty times. "I have had a portable barometer not less than seven times upon the summit, and can fully answer for the accuracy of the barometrical variation between the Valley of Wythburn at the foot and the summit of the mountain .... from barometrical re- sults I calculate the height of the road at the foot of the mountain to be 180 yards above the level of the sea; also the summit of the mountain to be 850 or 860 yards above the road, making a total of 1,035 yards perpendicular elevation above the sea." The Ordnance Survey makes Helvellyn 1,039 yards. His summers were spent, as has been said, at the English Lakes, He did not usually make these h2 116 JOHN DALTON. excursions alone. Often he met there old Cumberland friends, or he was accompanied by some of the young people of the Johns family. These walks were not only of value from the point of view of meteorology, but also from that of health, for Dalton says, " They were undertaken partly with the object of bringing into exercise a set of muscles which otherwise would have grown stiff." " To those who have seen him only on ordinary occasions," Miss John writes, "it is im- possible to convey an idea of his enthusiasm on those occasions. He never wearied." Jonathan Otley, the well-known writer of the first good guide to the Lake Mountains, who often went with Dalton on these excursions, thus describes some of his wanderings with the great Manchester chemist : — " On the 6th day of July, 1812, I first met with Mr. Dalton on Skiddaw. Observing that he carried a barome- ter, I introduced myself by saying that I had seen a little of the use of the barometer in measuring the heights of mountains, having about three years previously accom- panied the Rev. Dr. Pearson to Skiddaw, where I saw its application; and he having left the instrument in my possession, I had afterwards made some experiments with it myself. Mr. Dalton then told me he had twice, with a guide from Langdale, attempted to reach the top of Scawfell, but the weather at both times becoming unfavourable, the result had not been satisfactory ; and that he proposed to reach it from Wasdale Head, that he expected two friends from Kendal to join him next day, and if I would go along with them they would be glad of my company. Accordingly at noon next day his two friends arrived, and each of us being formally introduced by name — John Dalton, Thomas Wilson, Wilson Sutton, and Jonathan Otley — off we set for Wasdale Head, where DALTON AS A PEDESTRIAN. 117 -we expected to obtain quarters for the night at some of the farmhouses. " Passing through Borrowdale, we called at the black- lead mine, where we saw a good quantity of the mineral, as they had recently opened out a productive sop. From thence, shaping our course over the trackless mountain towards Wasdale Head, the clouds lowered so fast that we were presently enveloped in a thick mist. And in our anxiety to reach our destination before the early time at which the inhabitants of these vales retire to rest Mr. Dalton was leading the way at a brisk pace, while the other two gentlemen were not able to keep up. I, in the middle place, had some difficulty in keeping them all within sight, and in. such a case it would not have been safe to have been separated farther. Having passed the first ridge and descended a little towards the lower edge of the mist, the first object that came in view was a huge rock, which, from its indistinct appearance, I at first took to be Lingmel Crag, on the further side of Wasdale Head ; but on getting a little lower we were undeceived by see- ing the bright silvery stream of the Lisa meandering down the Vale of Ennerdale on its way to the lake. Having reached the peacefiil vale of Wasdale Head — a place at that time not much visited by strangers — we began to look out for lodgings. At the first house, Mr. Isaac Fletcher's, we obtained lodgings for two, which was very acceptable to our two Kendal friends ; Mr. Dalton and I journeying on to Mr. Thomas Tyson's, where we found good accommodation. " Dr. Dalton usually travelled by stage as far as the coach served his purpose; the rest of his journeyings were chiefly accomplished on foot. He used to say that a little mountain exercise brought into play a certain set of muscles which would otherwise turn rigid and inac- tive. He was active and persevering in climbing a moun- tain ; especially when he came in sight of the goal there was no keeping pace with him. In descending, or on rough ground, I was fully his equal : my stronger shoes enabled me to venture more freely. The barometer which he carried was of the most simple construction, yet its 118 JOHN DALTON. action was more intelligible than some fitted up in a more expensive way. His eyes, though subject to some defects, were very exact in estimating small divisions of space. His mode of calculating altitudes generally came out something higher than what has subsequently been given in the Ordnance Survey ; but for his purpose the greatest exactness was not required. In later years he declined bringing his barometer, as he had the privilege of using one belonging to the Eev. Dr. Pearson, and afterwards one of my own construction. He was never averse to taking Matthew Jopson's advice in taking a little brandy to mix with the water of Brownrigg Well, but he was very abstemious in using it. Although these excursions have been undertaken chiefly as recreations, they have not been without their use. They assisted in the investigation of the constitution of the atmosphere, and we have been enabled to make a step in advance of our predecessors in the geographical delineation of the district. Although the doctor always treated me as a companion, he would never permit me to go without some pecuniary remuneration — I must not say for loss of time, as no time could be said to be lost that was spent in his company, he was so affable and communi- cative. When, on the last-mentioned occasion, I would have declined what he offered, he said I must take it ; it might probably be the last — and, as far as regarded mountain excursions or journeying in company, so it was. I saw him at Keswick two or three times after that, but still with a kind of melancholy pleasure." Dalton never forgot his native village and its bucolic but original inhabitants, and he often revisited the home of his childhood. He used to lodge at the Globe Inn, Cockermouth, where he entertained some of his friends to supper. Next morning he rose betimes and made his way to Eaglesfield, where he was always glad to meet his old "weel-kennt" acquaintances. He spoke his native Cumbrian as EAGLESPIELD REVISITED. 119 well in his old age as when as a youngster he ploughed his father's fields. " What, ye'll be thrang w'yer hay," he would remark to the yeomen as they tossed the sweet-smelling grass of the uplands ; and being asked indoors, he would sit down and light his pipe and " have a real gude crack " about old days. There he would meet his former friend and associate, William Alderson, who, sitting over the fire in his cottage, and not seeing any use in a fender, would kick the stray cinders behind the grate with the wooden clogs which all the North-country people then wore. Often " the Doctor's " party at the Lakes was a large one, and night-quarters had to be sought in some of the farmhouses in the outlying districts. In those days there were none of the great hotels in which travellers by the hundred can now be accommo- dated, and many shifts had to be resorted to by land- lords and their families to put up a belated guest. Once, describing to a young lady friend his adven- tures in Lake-land, Dalton was asked whether he had ever seen the celebrated beauty of that day, Mary of Buttermere, the daughter of the landlord of the only inn, " The Fish," in that district. " No," said the Doc- tor, " but I have slept in her bed ; for one night I arrived at Buttermere, wet and tired, to find the inn full; but by dint of persuasion a room was found for me, and Mary got out of her bed and I got in, and right warm I found it, I can tell thee." In spite of his "infirmity of vision," Dalton was 120 JOHN DALTON. alive to, and impressed by, the beauties of Nature, as the following extract from his journal in 1796 shows : — " Augiist 22iid, 1796. " We had a pleasant ride from Kendal for eight miles, when the grand scenery of the Lakes opened upon us with full force. The head of Windermere and about half of the lake, with the surrounding hills skirted with wood, formed a fine and capacious amphitheatre which we had in view more or less till we arrived at Lowood. Drank tea there, and immediately after took a boat out to a central part of the lake, when we beheld the sun descend- ing below the summit of Langdale Pikes, whilst its rays still continued to gild the delightful landscape on the opposite shore. . . . Came off the lake, then proceeded to Ambleside, winding roimd the still lake by twilight. Went out about ten to view the night scene. The atmosphere was as clear as possible : Jupiter and the fixed stars shone with uncommon splendour and suggested an unusual proximity. The moon, risen, but not above the mountains, cast a glimmering light upon the rocky hills just opposite and produced a fine effect. These circum- stances, together with the awful silence around, would have persuaded us we had been transferred to some other planet." Dalton's first impressions of London, which he visited in May, 1792, are worth recording, and they were not favourable. "London," he say«, "is a most surprising place, worth one's while to see once ; but the most disagreeable place on earth for one of a contemplative turn to reside in." He does not appear, on this occasion, to have made the acquaintance of any of the Metropolitan savants with whom he after- wards became intimate. The object of his visit was a NANCY WILSON, OP THORNTON. 121 religious one, and arose from a wish to attend tlie yearly meeting of " Friends," who, in the spring month, are in the habit of congregating in London from all parts of the kingdom. If in science he was an innovator, so, too, in the religious services of the Quaker meeting-house he appears to have desired to introduce new methods, for he and another equally ardent spirit actually proposed to the assembled elders that organ-music should be used in the "silent service." But to praise God by machinery was, and is still, thought to savour of too much of the stage, and the proposal, as we might imagine, fell very flat. Dalton often used to say that he had no time to marry; but for all that, in his more youthful days at any rate, he was not insensible to the charms of the fair sex. On looking through the Hortus Siccus made by Dalton, and now in the possession of the Literary and Philosophical Society of Manchester, I came upon a dried specimen of the lady's slipper (^Oypridium caleeolus) — a charming orchid, very abundant in the Yorkshire dales in 1790, but now scarce even in its most favourite haunts. Under this speciaien I found in Dalton's handwriting the follow- ing inscription: "Presented to me by Nancy Wilson, of Thornton-in-Craven." That Nancy had touched the staid Quaker to his heart's core appears from the following remarks of Miss Johns, who knew him better than almost anyone else : " He used to mention with the warmest interest, and with deep sensibility. 122 JOHN D ALTON. a most amiable and accomplished Quaker friend who died young, but whose memory he ever cherished with the fondest regret. There was nothing but friendship in this, as she was engaged when he became acquainted with her. He had a letter and some verses of this lady's, with which we could by no means prevail upon him to part, or even to let us look at, though he read them to us with a faltering voice, and, what was very rare with him, with eyes suffused with tears, repeating as he ended, ' Poor Nancy, poor Nancy.' " In a letter to Robinson he allows that he had fallen a victim to the blandishments of the hand- somest woman in Manchester, and a widow to boot. But this, it seems, was a transient affair. Probably more serious for the young man than the case of the widow was his acquaintance with Hannah, the daughter of a Lancaster Friend. The following letters describe his feelings so well that they are worth reproducing. Observe his caution to his brother Jonathan: "I would not have thee commu- nicate my sentiments to others." " It seems that another of your maids is become mis- tress — a good omen for the next, whoever she may be. Methinks there may be a question started from some side of the fire when this is read — 'I wonder whether John is going to marry yet or not ? ' I may answer that my head is too full of triangles, chymical processes, and electrical experiments, etc., to think much of marriage. I must not, LETTERS TO BROTHER JONATHAN. 123 however, omit to mention that I was completely Sir Eoger de Coverleyed a few weeks ago. " The occasion was this : Being desired to call upon a widow — a Friend, who thought of entering her son at the academy — I went, and was struck with the sight of the most perfect figure that ever human eyes beheld, in a plain but neat dress; her person, her features, were engaging beyond all description. Upon inquiry after, I found she was universally allowed to be the handsom- est woman in Manchester. Being invited by her to tea a few days after, along with a worthy man here, a public Friend (a Quaker minister), I should have in any other circumstances been highly pleased with an elegant tea equipage, American apples of the most delicious flavour, and choice wines : but in the present these were only secondary objects. Deeming myself, however, full proof against mere beauty, and knowing that its concomitants are often ignorance and vanity, I was not under much apprehension. But she began to descant upon the excel- lence of an exact acquaintance with English grammar and the art of letter- writing ; to compare the merits of Johnson's and Sheridan's dictionaries ; to converse upon the use of dephlogisticated marine acid in bleaching; upon the effects of opium on the animal system, etc. etc. I was no longer able to hold out, but surrendered at dis- cretion. During my captivity, which lasted about a week, I lost my appetite, and had other symptoms of bondage about me, as incoherent discourse, etc., but have now happily regained my freedom. Having now wrote till I have tired my hand, and probably thine eyes in reading, I shall conclude Avith my love to Cousin Ruth and thyself and to all enquiring friends, ^^ , j. „ Again he writes : — " I may here observe that it has been my lot for three years past to be daily gaining acquaintance of both sexes. I have consequently had opportunities of estimating and comparing characters upon a pretty extensive scale. Since my first introduction to , twelve months ago, I have 124 JOHN DALTON. spent a day or two with them at six different interTals, with the highest satisfaction, as I have never met with a character so finished as Hannah's. What is called strength of mind and sound judgment she possesses in a very eminent degree, with the rare coincidence of a quick apprehension and the most lively imagination. Of sensibility she has a full share, but does not affectedly show it on every trivial occasion. The sick and the poor of all descrip- tions are her personal care. Though undoubtedly accus- tomed to grave and serious reflections, all pensiveness and melancholy are banished from her presence, and nothing but cheerfulness and hilarity diffused around. Her imcommon natural abilities have been improved by cultivation, but art and form do not appear at all in her manner: all is free, open, and unaffected. Extremely affable to all, though everyone sees and acknowledges her superiority, no one can charge her with pride. She is, as might be expected, well pleased with the conver- sation of literary and scientific people, and has herself produced some essays that would do credit to the first geniuses of the age, though they are scarcely known out of the family, so little is her vanity. Her person is agreeable, active, and lively. She supports conversation, whether serious, argumentative, or jocular, with uncom- mon address. In short, the tout ensemble is the most complete I ever beheld. Next to Hannah, her sister Ann takes it, in my eye, before all others. She is a perfect model of personal beauty. I do not know one that will bear a comparison with her in this respect — at least in our society. With abilities much superior to the gener- ality, she possesses the most refined sensibility, but in strength of mind and vigour of understanding must yield to her elder sister. I dwell with pleasure upon the character of these two amiable creatures, but would not have thee communicate my sentiments to others." From the age of twelve up to his death Dalton earned his living as a schoolmaster, but not an ordinary one ; for having set his pupils to their HIS FRUGALITY. 125 lessons, and having given them a hint how to pro- ceed, he would leave them pretty much alone, believ- ing in the doctrine, which he had practised through- out his life, that self-education is the only true one. Thus he found himself at liberty to look after his own experimental work, or to make the calculations which they entailed. Inheriting the spirit of his frugal and economical forbears, he always had enough for his simple needs ; indeed, when sixty years of age, he considered himself a moneyed man. To begin with, he charged only Is. per lesson, after a while he increased his fee to Is. 6d., and ultimately demanded and obtained the maximum of 2s. 6d. per hour ! One day Sir James Bardsley, a well-known Manchester physician of the day and a friend of Dalton's, on calling upon him noticed half-a-crown Ijdng on the table. " You throw your money about carelessly," said he. " Ay," answered Dalton, " a woman has just gone away that I have been teaching a bit of arith- metic to, and thou sees she has left me half-a-crown." His diary abounds with passages showing his scrupu- lous care about money matters, and also his interest in getting his money's worth : " Mr. J. Pearson and I walked to Hayfield (four miles), breakfasted there on tea, two basins of milk, four eggs, bread and butter, muffins, etc. ; for what ? for 9d. apiece ! " But besides his ordinary tutorial work Dalton taught pupils in his laboratory, and for this he charged the exorbitant sum of 3s. 6d. He also acted as a professional or 126 JOHN DALTON. consulting chemist, and earned half-a-guinea now and again for a water analysis, for which at the present day the charge would be twenty times as much. Then he frequently gave courses of lectures, as we shall see, not only in Manchester, but in London, Edinburgh, and elsewhere. We now pass on to trace the development of the greatest work of his life — the discovery of the laws of Chemical Combination and the foundation of the Atomic Theory. CHAPTER VI. dalton's atomic theoby. Although this memoir does not profess to be a history of the Atomic Theory concerning the consti- tution of matter from the earliest ages to the time of Dalton, but has a much less ambitious aim — namely, to give an account of the life and work of the great Man- chester chemist, and of the Atomic Theory of chemistry as developed by him — it may be well in a few sen- tences to call to mind what had been thought and done, as regards this subject, by others before his time. From very early times, even up to the present, two opposing views have been held respecting the constitution of matter. The one of these is the atomic view, the other the dynamic. According to the first of these, matter is divisible into minute, in- destructible, unchangeable particles called atoms (a privative, re/Mva, Icuf). According to the second, no limit is placed on the divisibility of matter, and there- fore no finite particles exist, and all we observe is explained by attractions or repulsions. The one 127 128 JOHN DALTON. involves the discontinuity of matter, the other involves its continuity. The atomic view was held not only by the Greek and Roman philosophers, but also by the wise men of the East in Egypt and India. And the conviction that matter was not of haphazard constitution, but was arranged according to definite laws, appears to have been long borne in upon the human mind, and is expressed in the well-known words : " God ordered all things by measure, number, and weight." Newton was a staunch upholder of the Atomic Theory. " It seems," * says Newton, " probable to me that God in the beginning formed matter in solid, massy, hard, impenetrable, moveable particles, of such sizes and figures, and with such other properties, and in such proportion, as most conduced to the end for which He formed them ; and that these primitive particles, being solids, are incomparably harder than any porous bodies compounded of them; even so very hard as never to wear or break in pieces, no ordinary power being able to divide what God Him- self made one in the first creation. While the particles continue entire they may compose bodies of one and the same nature and texture in all ages ; but should they wear away, or break in pieces, the nature of things depending on them would be changed. Water and earth composed of old worn * Horsley's "Newton," vol. iv. p. 260. Quoted by Dalton. THE ATOMIC THEORY. 129 particles and fragments would not be of the same nature and texture with water and earth composed of entire particles in the beginning. And therefore, that nature may be lasting, the changes of corporeal things are to be placed only in the various situations, and new associations and motions of these permanent particles, compound bodies being apt to break, not in the midst of solid particles, but where those particles are laid together and only touch at a few points. . . . God is able to create particles of matter of several sizes and figures, and in several proportions to the space they occupy, and perhaps of different densities and forces. ... At least, I see nothing of con- tradiction in all this. . . . Now, by the help of these principles, all material things seem to have been composed of the hard and solid particles above mentioned — variously associated, in the first crea- tion, by the counsel of an intelligent agent." It is, however, to Dalton, and to him alone, that the honour of founding a chemical atomic theory is to be ascribed. It was he who first explained the facts of chemical combination by a theory which has stood the test of time, and is not contradicted by any known phenomenon of chemical action. Dalton, it must be here remarked, never pretended — nor, indeed, has it ever been urged on his behalf by others — that he was the first to propose an atomic theory of matter. He knew quite well that such views had long been the property of mankind. " These observations," he says, I 130 JOHN DALTON. " have tacitly led to the conclusion which seems uni- versally adopted, that all bodies of sensible magnitude, whether solid or liquid, are constituted of a vast number of extremely small particles bound together by a force of attraction," etc. In the preceding chapters it has been pointed out that Dalton's mind was of a corpuscular turn. He was thoroughly saturated with the Newtonian doctrine of atoms; he was in the habit, from his early days, of looking at things from an atomic point of view. He was never tired of explaining that "homogeneous elastic fluids are constituted of particles." It was in his volume on Meteorology that he insisted on the separate existence of aqueous vapour from the other constituents of the air, and this was the first germ of his Atomic Theory, because he viewed the gases as consisting of independent atoms. There has been a considerable amount of dis- cussion as to how Dalton arrived at those important conclusions, and various surmises on the subject have from time to time been made. The matter is now set at rest for ever by Dalton himself. Amongst the " Dalton papers " in the possession of the Manchester Literary and Philosophical Society I have been fortu- nate enough to find the manuscript notes prepared by Dalton for the course of lectures delivered in- the winter of 1809-10, at the Royal Institution, Albemarle Street. These notes are of the greatest interest, be- cause they give his own explanation of the genesis of DALTON A NEWTONIAN. 131 his ideas regarding the Atomic Theory of chemistry, and as they have not been hitherto published, I need scarcely apologise for now presenting them verbatim. From what follows it will be clear that it was the application of the principle of the Newtonian atom to the constitution of the gases contained in the atmosphere that led Dalton to his Atomic Theory. The printed syllabus of the seventeenth lecture, delivered on Jan. 27th, 1810, is as follows : — "Saturday, January 27th, at 2 o'clock. Mr. Dalton, Natural Philosophy. Lecture 17.* " Chemical Elements. — Divisibility of matter consid- ered. Elastic fluids exhibit matter in extreme division. Other bodies constituted of atoms as well as elastic fluids. All atoms of the same matter alike in weight, bulk, etc. Bodies deemed simple until they are decom- posed. Chemical synthesis considered. Tables of arbi- trary marks representing the Elements." For this lecture, Dalton's manuscript notes are as follows : — " As the ensuing lectures on the subject of the Chemical Elements and their combinations will perhaps be thought by many to possess a good deal of novelty, as well as importance, it may be proper to give a brief historical sketch of the train of thought and experience which led me to the conclusions about to be detailed. Having been long accustomed to make meteorological observations, and to speculate upon the nature and constitution of the atmosphere, it often struck me with wonder how a com- pound atmosphere, or a mixture of two or more elastic fluids, should constitute apparently a homogeneous mass, * The course consisted of twenty lectures on mechanics, pneu- matics, etc., and Dalton's first lecture had been delivered on December 21st, 1809. I2 132 JOHN DALTON. or one in all mechanical relations agreeing with a simple atmosphere. " Newton had demonstrated clearly in the 23rd Prop, of Book II. of the 'Prineipia' that an elastic fluid is constituted of small particles or atoms of matter which repel each other by a force increasing in proportion as their distance diminishes. But modern discoveries hav- ing ascertained that the atmosphere contains three or more elastic fluids of different specific gravities, it did not appear to me how this proposition of Newton's would apply to a case of which he, of course, could have no idea. The same difficulty occurred to Dr. Priestley, who discovered this compound nature of the atmosphere. He could not conceive why the oxygen gas, being specifically heaviest, should not form a distinct stratum of air at the bottom of the atmosphere, and the azotic gas one at the top of the atmosphere. Some chemists upon the Conti- nent — I believe, the French — found a solution of this difficulty (as they apprehended). It was chemical affinity. One species of gas was held in solution by the other; and this compound in its turn dissolved water — hence evaporation, rain, etc. This opinion of air dissolving water had long before been the prevailing one, and natu- rally paved the way for the reception of that which fol- lowed — of one kind of air dissolving another. It was objected that there was no decisive marks of chemical union when one kind of air was mixed with another. The answer was, that the affinity was of a very slight kind, not of that energetic cast that is observable in most other cases. I may add, by-the-bye, that this is now, or has been till lately, I believe, the prevailing doc- trine in most of the chemical schools in Europe. In order to reconcile — or, rather, adapt — this chemical theory of the atmosphere to the Newtonian doctrine of repulsive atoms or particles, I set to work to combine my atoms upon paper. I took an atom of water, another of oxygen, and another of azote, brought them together, and threw around them an atmosphere of heat, as per diagram. I repeated the operation, but soon found that the watery particles were exhausted (for they make but OBiGEsr OP dalton's theory. 133 a small part of the atmospliere). I next combined my atoms of oxygen and azote one to one; but I found in time my oxygen failed. I then threw all the remaining particles of azote into the mixture, and began to consider how the general equilibrium was to be obtained. My triple compound of water, oxygen, and azote were wonder- fully inclined, by their superior gravity, to descend and take the lowest place. The double compounds of oxygen and azote affected to take a middle station ; and the azote was inclined to swim at the top. I remedied this defect by lengthening the wings of my heavy particles — that is, by throwing more heat around them, by means of which I could make them float in any part of the vessel. But this change, imfortunately, made the whole mixture of the same specific gravity as azotic gas. This circum- stance would not for a moment be tolerated. In short, I was obliged to abandon the hypothesis of the chemical eonstitution of the atmosphere altogether as irreconcile- able to the phenomena. There was but one alternative left — namely, to surround every individual particle of icater, of oxygen, and of azote with heat, and to make them respectively centres of repulsion, the same in a mixed state as in simple state. This hypothesis was equally pressed with difficulties, for still my oxygen would take the lowest place, my azote the next, and my steam would swim upon the top. In 1801 I hit upon an hypothesis which completely obviated these difSculties. According to this, we were to suppose that atoms of one kind did not repel the atoms of another kind, but only those of their own kind. This hypothesis most effectu- ally provided for the diffusion of any one gas through another, whatever might be their specific gravities, and perfectly reconciled any mixture of gases to the Newto- nian theorem. Every atom of both or all the gases in the mixture was the centre of repulsion to the proximate particles of its own kind, disregarding those of the otheJ kind. All the gases united their efforts in counteracting the pressure of the atmosphere, or any other pressure that might be exposed to them. "This hypothesis, however beautiful might be its 134 JOHN DALTON. application, had some improbable features. We were to suppose as many distinct kinds of repulsive powers as of gases ; and, moreover, to suppose that heat was not the repulsive power in any one case — positions certainly not very probable. Besides, I found from a train of expts. which have been published in the ' Manchester Memoirs ' that the diffusion of gases through each other was a slow process, and appeared to be a work of considerable effort. " Upon considering this subject, it occurred to me that I had never contemplated the effect of difference of size in the particles of elastic fluids. By size* I mean the hard particle at the centre and the atmosphere of heat taken together. If, for instance, there be not exactly the same number of atoms of oxygen in a given volume of air as of azote in the same volume, then the sizes of the particles of oxygen must be different from those of azote. And if the sizes be different, then — on the supposition that the repulsive power is heat — no equilibrium can be_ established by particles of unequal sizes pressing against each other. (See diagram.) "This idea occurred to me in 1805. f I soon found that the sizes of the particles of elastic fluids must be different. For a measure of azotic gas and one of oxy- gen, if chemically united, would make nearly two meas- ures of nitrous gas, and those ttvo could not have more atoms of nitrous gas than the one measure had of azotic or oxygen. (See diagram.) Hence the suggestion that all gases of different kinds have a difference in the size of their atoms ; and thus we arrive at the reason for that diffusion of every gas through every other gas, without calling in any other repulsive power than the well-known one of heat. This, then, is the present view which I have of the constitution of a mixture of elastic fluids." With these introductory remarks, Dalton pro- ceeded to illustrate the several points referred to in * By " size " he perhaps includes the idea of weight. t Dalton seems here to have mistaken the date, for in the autumn of 1803 he gave a table of the relative weights of the ultimate atoms (see page 106). "sizes" of the ultimate particles. 135 the syllabus. The notes he made for his own guidance are as follows : — " 1. Divisibility of matter considered. Atoms, (^ee Newton's Ideas^ " 2. Elastic fluids exhibit matter in extreme division. Newton, B. 2, Prop. 23. {See diagram.) " Hydrogen and oxygen cannot be broken down into finer kinds by electricity, like flour, etc. "Compound gases, as nitrous, carbonic acid, are sep- arated into their ulterior elements by electricity. {See diagram — atmosphere.) "3. Other bodies constituted of atoms as well as elastic fluids^ — charcoal, sidphur, phosphorus. Metals, by combining with atoms of elastic fluids, shew that they have atoms. "4. All atoms of the same kind alike in wt., bulk. "5. Atoms of different kinds unequal in wt., etc. {See Newton.) " 6. Bodies deemed simple till they are decomposed. " 7. Chemical synthesis. Exhibit two particles.* {See also Newton.) " 8. Table of arbitrary marks. "9. Gay-Lussac's notion." t Dalton concluded this lecture with the following words : — "The different sizes of the particles of elastic fluids under like circumstances of temperature and pressure being once established, it became an object to determine * The writer remembers a pupil, to whom he had explained the Atomic Theory by help of wooden blocks, giving the following answer to the question, "Describe Dalton's Atomic Theory : " — "Dalton's Atomic Theory consists of cubical blocks of wood painted various colours." t It must have been interesting to have heard Dalton's remarks on this "notion." 136 JOHN D ALTON. the relative sizes and weights, together with the relative number, of atoms in a given volume. This led the way to the combinations of gases, and to the number of atoms entering into such combinations, the particulars of which will be detailed more at large in the sequel. Other bodies besides elastic fluids — namely, liquids and solids — were subject to investigation, in consequence of their combin- ing with elastic fluids. Thus a train of investigation was laid for determining the number and weight of all chemical elementary principles which enter into any sort of combination one with another." "Lecture 18, Jan. 30th, 1810. Chemical Elements. " Syllabus; — Combination of Simple Atoms, constituting Compound Atoms. — Manner of finding tlie relative Weights of Atoms. — Arrangement of tliree or more Atoms forming one Compound — of Water, of Ammonia, of tiie various Compounds of Azote and Oxygen. "In the last lecture we endeavoured to shew that matter, though divisible in an extreme degree, is never- theless not infinitely indivisible — that there must be some point beyond which we cannot go in the division of matter. The existence of these ultimate particles of matter can scarcely be doubted, though they are proba- bly much too small ever to be exhibited by microscopic improvements. " I have chosen the word atom to signify these ulti- mate particles in preference to particle, molecule, or any other diminutive term, because I conceive it is much more expressive ; it includes in itself the notion of indi- visible, which the other terms do not. It may, perhaps, be said that I extend the application of it too far when I speak of compound atoms; for instance, I call an ulti- mate particle of carbonic acid a compound atom. Now, though this atom may be divided, yet it ceases to become carbonic acid, being resolved by such division into char- coal and oxygen. Hence I conceive there is no incon- sistency in speaking of compound atoms, and that my meaning cannot be misunderstood. " It has been imagined by some philosophers that all DALTON ON "CHEMICAL ELEMENTS." 137 matter, however unlike, is probably the same thing, and that the great variety of its appearances arises from cer- tain powers communicated to it, and from the variety of combinations and arrangements of which it is susceptible. From the notes I borrowed from Newton in the last lect- ure this does not appear to have been his idea. Neither is it mine. I should apprehend there are a considerable number of what may properly be called elementary princi- ples, which never can be metamorphosed one into another by any power we can controul. We ought, however, to avail ourselves of every means to reduce the number of bodies or principles of this appearance as much as pos- sible; and, after all, we may not know what elements are absolutely indecomposable and what are refractory, because we do not apply the proper means for their reduction. We have already observed that all atoms of the same kind, whether simple or compound, must neces- sarily be conceived' to be alike in shape, weight, and every other particular." "Lecxueb 19, Jan. 31st, 1810. Chemical Elements. " Syllabus : — Compounds of Charcoal and Oxygen. — Carbonic Oxide. — Carbonic Acid. — Compounds of Charcoal and Hydrogen. — Ole- fiant Gas. — Sulphur, Phosphorus, and their Compounds. — Earths. — Metals. — Metallic Oxides and Sulphurets. "In the preceding investigations on the number and weights of the elementary principles constituting water, ammonia, and the various compounds of azote and oxygen, you will have remarked that the conclusions were derived principally from the facts and experience of others, with- out any additional facts of my own discovery that merit particular notice. "The composition and decomposition of water had been ascertained by British and foreign chemists; that of ammonia by Berthollet and several others. The com- pounds of azote and oxygen had been successively devel- oped by Cavendish, Priestley, Davy, and others. I may, however, observe that the nitrous comxiounds have occupied a great portion of my time and attention at different sea^ sons. The elegant and instructive experiments on the IBS JOHN dalton. effect of electricity on nitrous gas deserve notice. By electrifying nitrous gas over water, in a short time one hundred measures are reduced to twenty-four which upon examination are pure azote. "1. Theory of it explained. "2. Theory of the formation of nitric acid in Mr. C.'s (Cavendish) experiment. ""The simple and easy method of combining the least portion of oxygen with the greatest of nitrous gas, which I pointed out in the last lecture, was the result of my own investigation, and aifords a convincing proof of the real nature of what is called nitrous acid, which is con- stituted of one atom of oxygen united to two of nitrous gas (see Figure). " Erom the preceding remarks it will be perceived that I advanced thus far in my theoretic progress without meeting with much obstruction. The way had been paved by others. But when I directed my views to the compounds of charcoal and oxygen, and charcoal and hydrogen, I found that all the commonly received doc- trines were adverse to my proceeding and irreconcileable with my views. "Mr. Tennant's experiments in the Philos. Transact., 1797, had shewn the identity of diamond and charcoal in a chemical point of view ; but the succeeding experiments of Guyton Morveau, on the combustion of diamond, sup- planted the former in the judgement of a great part of our chemists; diamond was concluded to be a simple body, and charcoal the oxide of diamond. Mr. Cruick- shanks soon after discovered the gas called carbonic oxide. The doctrine of the compounds of charcoal, or rather diamond and oxygen, then stood thus : Parts. Diamond . 18 Oxygen . . 10 28 Charcoal. Oxygen . • 41 69 Carbonic oxide. Oxygen . . 31 100 Carbonic acid. DALTOK ON "CHEMICAL ELEMENTS." 139 " A very little reflection conTinced me that the doctrine of charcoal being an oxide of diamond was highly improb- able ; and experience confirmed the truth of Lavoisier's conclusion, that 28 parts charcoal + 72 oxygen constitute carbonic acid; also that carbonic oxide contained just half the oxygen that carbonic acid does, which, indeed, had been determined by Clement and Desormes, two French chemists, who had not, however, taken notice of this remarkable result." In the last lecture of this course, Dalton explained his singular and, as it turned out, altogether erro- neous views respecting the chemical nature of chlo- rine, hydrochloric, and hydrofluoric acids. " Lecture 20, February 3rd, 1810. Chemical Elements. " Syllabus ; — Fluoric, Muriatic, Oxymuriatic, Hiperoxymuriatic and Acetic Acids. — Weights of tlie Component Parts of Neutral Salts from Theory and Experiment. — Action of Common Electricity on Compound Gases and Gaseous Mixtures. — Conclusion of the Course. " When we consider the very important part which the two elements of hydrogen and oxygen seem to perform in the arrangement of chemical compounds, we are inclined to wonder that no more than one compound of these two elements themselves should be found. " Water, that most beneficial essential of all liquids, is formed of oxygen and hydrogen. Besides this one, there is not a compound of these two elements generally known and recognised as such. It is singular if we have not somewhere a principle consisting of two atoms of oxygen and one of hydrogen, or two of hydrogen and one of oxy- gen. The former of these ought to be an