Dalton, John (1766-1844) (DNB00)
|←Dalton, John (1726-1811)||Dictionary of National Biography, 1885-1900, Volume 13
Dalton, John (1766-1844)
DALTON, JOHN (1766–1844), chemist and natural philosopher, was born at Eaglesfield, near Cockermouth in Cumberland, on 6 Sept. 1766. His father, Joseph Dalton, was a poor weaver, undistinguished either for parts or energy, who married in 1755 Deborah Greenup, a woman of strong character, and, like himself, a member of the Society of Friends. The Greenups of Caldbeck were a respectable family of yeomen; the Daltons were husbandmen and artisans, although Joseph Dalton inherited, shortly before his death in 1787, a freehold of sixty acres acquired by his father Jonathan, a shoemaker at Eaglesfield. John Dalton was the youngest of three children who reached maturity out of six born to Joseph and Deborah Dalton. While attending a quakers' school kept by Mr. John Fletcher at Pardshaw Hall, he entered, at the age of ten, the service of Mr. Elihu Robinson, a quaker gentleman of fortune and scientific attainments, whose notice was quickly attracted by Dalton's love of study. He gave him evening lessons in mathematics, and so effectually stimulated the boy's desire for self-improvement, that, on Fletcher's retirement in 1778, he was able to set up school on his own account. His first schoolroom was a barn at Eaglesfield, soon exchanged for the quakers' meeting-house. His pupils were boys and girls of all ages, from infants whom he held on his knee while he taught them their letters, to robust youths who met his reprimands with pugilistic challenges. The weekly pence gathered from them, to the total amount of about five shillings, were eked out with the sale of stationery; while his own education was pursued with a zeal exemplified by his copying out verbatim a number of the ‘Ladies' Diary’ which fell into his hands.
After two years the school was closed, and Dalton took to field work as a means of subsistence. In 1781, however, he joined his brother Jonathan as assistant in a school at Kendal, which they carried on independently on the retirement, in 1785, of the master and their cousin, George Bewley. Their sister Mary acted as housekeeper, and their parents visited them from time to time, bringing home-produce, and accomplishing the distance of forty-four miles from Eaglesfield on foot in one day. About sixty pupils of both sexes attended, including some boarders, and the profits reached one hundred guineas in the first year. But the popularity of the brothers did not increase. They were uncompromising in their discipline, and somewhat over stern in punishment, although John was the milder of the two, and was, besides, too much absorbed in private study to look out for delinquencies. His progress may be judged of from a syllabus of a course of lectures on natural philosophy issued by him 26 Oct. 1787, including mechanics, optics, pneumatics, astronomy, and the use of the globes. They were repeated in 1791, when the price of admittance was reduced from one shilling to sixpence.
Dalton probably read more in the twelve years he spent at Kendal than in the fifty of his remaining life. There was gathered the stock of knowledge which served as the basis of all his future researches. There also he acquired habits of close and meditative observation. His acquaintance with Gough, the blind philosopher described by Wordsworth in the ‘Excursion’—‘Methinks I see him how his eyeballs roll'd,’ &c.—was of material assistance to him. He acquired with Gough's help a little Latin, French, and Greek, mastered fluxions, and studied the chief works of English mathematicians. Between 1784 and 1794 he tried his powers by diligently answering questions in the ‘Gentleman's’ and ‘Ladies' Diaries,’ winning by his solutions two high prizes. From Gough, too, he learned to keep a meteorological journal. The first entry commemorated an aurora borealis, 24 March 1787, and during the ensuing fifty-seven years two hundred thousand observations were recorded in it. He made hygrometers of whipcord, and supplied his friend Mr. Peter Crosthwaite, whom he engaged to make simultaneous observations at Keswick, with a rude barometer and thermometer of his own construction. Zoology and botany came in for a share of his attention. He furnished specimens of butterflies and dried plants to Mr. Crosthwaite's museum; compiled a ‘Hortus Siccus’ in eleven volumes, possessed a few years ago by Mr. T. P. Heywood of the Isle of Man; while his ‘Herbarium’ is still preserved in the Manchester Public Library.
Discouraged by his friends' advice from taking a learned profession, he accepted in 1793 a professorship of mathematics and natural philosophy in New College, Manchester, offered to him on Gough's recommendation. The proofs of his first book accompanied him on his removal from Kendal. The ‘Meteorological Observations and Essays’ (London, 1793) contained, as the author remarked forty years later, the germs of most of the ideas afterwards expanded by him into discoveries. A prominent section comprised the results of six years' auroral observations. He had detected independently the magnetic relations of the phenomenon, and concluded thence auroral light to be of purely electrical origin, and auroral arches and streamers to be composed of an elastic fluid of a ferruginous nature existing above our atmosphere. This hypothesis was further developed by Biot in 1820. From simultaneous observations at Kendal and Keswick Dalton derived for the aurora of 15 Feb. 1793 a height of a hundred and fifty miles; and recurring to the subject in later life, he calculated that the display of 29 March 1826 occurred a hundred miles above the earth's surface (Phil. Trans. cxviii. 302).
The essay in the same volume on evaporation was remarkable for the then novel assertion that aqueous vapour exists in the air as an independent elastic fluid, not chemically combined, but mechanically mixed with the other atmospheric gases. A second edition of the ‘Meteorological Essays’ was published in 1834, with the addition of some notes collected into an appendix, but with no alteration in the text. A catalogue of auroræ observed between 1796 and 1834 was added (p. 218).
Dalton was admitted a member of the Literary and Philosophical Society of Manchester 3 Oct. 1794, and read 31 Oct. a paper on ‘Extraordinary Facts relating to the Vision of Colours’ (Manchester Memoirs, v. 28). In it he gave the first detailed description of the peculiarity now known as ‘colour-blindness,’ discovered in himself through the attention paid by him in 1792, in the course of his botanical studies, to the hues of flowers. The defect was shared by his brother, and was studied on the continent under the name of ‘Daltonism.’ A post-mortem examination in his own case showed his explanation, by a supposed blue tinge in one of the humours of the eye, to have no foundation in fact.
He communicated to the same society on 1 March 1799 ‘Experiments and Observations to determine whether the Quantity of Rain and Dew is equal to the quantity of Water carried off by the Rivers and raised by Evaporation; with an Enquiry into the Origin of Springs’ (ib. v. 346). The last point, then much debated, was practically settled by Dalton's conclusion that springs are fed by rain. The same paper contained a further development of his theory of aqueous vapour, with the earliest definition of the ‘dew-point.’ It was followed on 12 April 1799 by an essay on the ‘Power of Fluids to conduct Heat’ (ib. v. 373), in which he combated Count Rumford's view that the circulation of heat in fluids is by convection solely. That entitled ‘Experiments and Observations on the Heat and Cold produced by the Mechanical Condensation and Rarefaction of Air,’ read on 27 June 1800 (ib. v. 515), contained the understated but important result that the temperature of air compressed to one-half its volume is raised 50° Fahrenheit.
Dalton's next communication gave him at once a European reputation. It consisted of four distinct essays comprised under a single heading, and was read on 2, 16, and 30 Oct. 1801 (ib. v. 535). The first was ‘On the Constitution of Mixed Gases,’ and expounded the doctrine of their mechanical diffusion, further developed in a paper read on 28 Jan. 1803. His inquiries into the relations of aqueous vapour and atmospheric air had convinced him that each follows its own laws of equilibrium, as if the other were absent. In 1801 he hit upon the explanatory idea, verified by numerous experiments, that the particles of every kind of elastic fluid are elastic only with regard to those of their own kind. This now discarded theorem rested on the fact (first observed by Dalton) that the quantity of aqueous vapour suspended in a given space depends upon temperature alone, and is unaffected by the pressure of air. Hence his generalisation that the maximum density of a vapour in contact with its liquid remains the same whether other gases be present or not. A further corollary was the extension of Boyle's law to a mixture of gases. In consonance with these views was Dalton's theory of the atmosphere, by which he regarded each of its constituents as forming a distinct envelope with its own proper limit of altitude (Phil. Trans. cxvi. 174). Observation, however, has shown no corresponding decrease in the proportion of oxygen at great heights.
The second essay of the set, ‘On the Force of Steam,’ gave the first table of its varying elasticity at temperatures from 32° to 212°, and described the ‘dew-point hygrometer’ (p. 582). The issue of some recent experiments was remarkably anticipated in the following sentence: ‘There can scarcely be a doubt entertained respecting the reducibility of all elastic fluids of whatever kind into liquids; and we ought not to despair of effecting it in low temperatures, and by strong pressure exerted upon the unmixed gases’ (p. 550). The third essay, ‘On Evaporation,’ showed the quantity of water evaporated in a given time to be strictly proportional to the force of aqueous vapour at the same temperature, and to be the same in air as in vacuo. The fourth, ‘On the Expansion of Gases by Heat,’ announced the law (arrived at almost simultaneously by Gay-Lussac) ‘that all elastic fluids expand the same quantity by heat’ (p. 537). This is known as ‘Dalton's law of the equality of gaseous dilatation.’ The fraction of their original volume, by which gases expand, under constant pressure, between 32° and 212°, was fixed by Dalton at 0.376 (since reduced to 0.367).
By these discoveries meteorology was constituted a science. They excited a strong interest, were immediately and widely discussed, and, with some minor deductions, made good their footing. From meteorology Dalton progressed naturally to chemistry. One of his leading mental characteristics was his proneness and power to realise distinctly what he thought about. His meditations on the atmospheric gases had led him to conceive them as composed of atoms, each surrounded by a very diffuse envelope of heat. That he should seek to follow them in their combinations was but an inevitable further step. His first chemical memoir was an ‘Experimental Enquiry into the Proportion of the several Gases or Elastic Fluids constituting the Atmosphere’ (Manch. Memoirs, i. 244, 2nd ser.). It was read on 12 Nov. 1802, and disclosed the insight obtained through study of the combinations of oxygen with nitrous gas, into the law of multiple proportions. With a view to explaining the various absorption of gases by water, he undertook to determine the comparative weights of their atoms. He remarked in a paper on the subject read 21 Oct. 1803 (ib. p. 271): ‘An inquiry into the relative weights of the ultimate particles of bodies is a subject, so far as I know, entirely new. I have lately been prosecuting the inquiry with remarkable success. The principle cannot be entered upon in this paper, but I shall just subjoin the results, as far as they appear to be ascertained by my experiments’ (ib. p. 286). A list of twenty-one atomic weights followed, that of hydrogen being taken for unity. To oxygen was assigned the number 5.5, to water 6.5, nitrogen 4.2, carbon 4.3. Inexact as these results were, their attainment marked an epoch in chemistry. There is reason to believe that they were inserted not long previous to the publication, in November 1805, of the paper containing them.
On 26 Aug. 1804 Dalton explained in conversation his theory of combining weights to Dr. Thomson, who in 1807 added a sketch of it to the third edition of his ‘System of Chemistry’ (iii. 424). The attention of the Royal Society was drawn to it by both Thomson and Wollaston in 1808; and Dalton, who had already lectured upon the subject at Edinburgh and Glasgow, published his views in ‘A New System of Chemical Philosophy’ (Manchester, part i. 1808, part ii. 1810). In this work he developed those primary laws of heat and chemical combination to which he had been gradually led since 1801, and laid the foundation of chemical notation by representing graphically the supposed collocation of atoms in compound bodies. Extended and revised tables of atomic weights were appended (pt. i. p. 219; pt. ii. 546). Dalton's curious inaptitude to receive the ideas of others was exemplified in an appendix disputing with Davy the elementary nature of chlorine, sodium, and potassium, and with Gay-Lussac the validity of his law of combining volumes, in reality, could he have seen it, a beautiful confirmation of his own law of combining weights.
The atomic theory was now fairly before the world. It met with very general applause, but only gradual acceptance. Berthollet and Davy were the most conspicuous objectors; but Davy retracted so far, after a few years, as to declare it the greatest scientific advance of recent times. The innovation of attributing fixed weights to the ultimate particles of matter, by which their combining proportions were strictly determined, gave a hitherto unknown definiteness to chemical analysis, and brought it within the scope of numerical calculation. There had, as usual, been partial anticipations. The claims of Dr. Bryan Higgins, professor of chemistry in Dublin, were brought forward by Davy in the Bakerian lecture of 15 Nov. 1810 (Phil. Trans. ci. 15), and still more emphatically by himself in 1814 (Experiments and Observations on the Atomic Theory). Higgins had undoubtedly, as early as 1789, laid a loose and temporary grasp on the doctrine of atomic combination, but its generalisation and proof were entirely due to Dalton, who read Higgins's ‘Comparative View’ only when he found himself under the suspicion of plagiarism from it. He declined all controversy in the matter, and it was publicly acknowledged by Davy in 1827 that Dalton ‘first laid down, clearly and numerically, the doctrine of multiples, and endeavoured to express, by simple numbers, the weights of the bodies believed to be elementary’ (Six Discourses, p. 128).
The outward circumstances of Dalton's life remained, meanwhile, unchanged. After the removal of New College to York in 1799 he supported himself by giving private lessons in mathematics at half-a-crown an hour, besides performing analyses and doing other work as a professional chemist at ridiculously low charges. His wants were few, and his habits economical to the verge of parsimony. Yet he could be generous on occasions. He gave largely, even at times lavishly, to objects deemed by him worthy; and in his later years he made liberal allowances to two distant female relatives. A fixed routine left no space in his laborious and abstemious life for recreation other than a game of bowls every Thursday afternoon at the ‘Dog and Partridge,’ and a yearly visit of intense enjoyment to Cumberland. He ascended Helvellyn in all between thirty and forty times. Asked the reason why he had not married, he replied, ‘I never had time.’ It is certain, however, that he cherished all his life the memory of one hopeless attachment.
One day in the autumn of 1804 Mrs. Johns, wife of the Rev. W. Johns, who kept a school in Faulkner Street, Manchester, seeing him pass, asked why he never called to see them. ‘I do not know,’ was the answer; ‘but I will come and live with you, if you will let me.’ He was as good as his word, took pos- session of their one spare bedroom, and resided with them in the utmost amity for twenty-six years. His laboratory was close at hand, on the premises of the Philosophical Society; and the neighbours could tell the hour to a minute by seeing him each morning read the thermometer outside his window.
His first visit to London was in 1792, for the purpose of attending the yearly meeting of Friends. He had then no scientific acquaintances, and described the metropolis to his brother as ‘a surprising place, and well worth one's while to see once, but the most disagreeable place on earth for one of a contemplative turn to reside in constantly.’ Under very different circumstances he returned thither in December 1803 to deliver a course of lectures at the Royal Institution, received, by his own perhaps sanguine account, with marked admiration. He was introduced to Sir H. Davy, but made no favourable impression, judging from the more critical than kindly sketch of his character penned at Rome in February 1829, and published by Dr. Henry (Memoir of Dalton, p. 216). Dr. Davy, his brother, too, conveyed his recollections of him in 1809–10 in the following unflattering terms: ‘Mr. Dalton's aspect and manner were repulsive. There was no gracefulness belonging to him. His voice was harsh and brawling; his gait stiff and awkward. his style of writing and conversation dry and almost crabbed. In person he was tall, bony, and slender. … Independence and simplicity of manner and originality were his best qualities. Though in comparatively humble circumstances, he maintained the dignity of the philosophical character’ (ib. p. 217).
He was at that time delivering three lectures a week at the Royal Institution. ‘I find myself just now,’ he wrote, ‘in the focus of the great and learned in the metropolis.’ Among his new acquaintances were Dr. Wollaston and Sir Joseph Banks. He had dined with James Watt at Birmingham in 1805; and foreign savants soon began to make their way to his dwelling in Manchester. Biot and Pelletan are named with others, the latter being unable to conceal his amazement at finding the great chemical philosopher engaged in giving a small boy a lesson in arithmetic.
Dalton was chosen secretary of the Manchester Philosophical Society in 1800, vice-president in 1808, and president in 1817, continuing in that office until his death. The Paris Academy of Sciences elected him in 1816 a corresponding member, and in 1830, in Davy's place, one of their eight foreign associates. He highly appreciated this compliment. Davy's offer of a nomination to the Royal Society had been refused by him in 1810, probably on grounds of expense; but he was elected in 1822, with no consent asked, and paid the usual fees. The first award of the annual prizes placed at the disposal of the Royal Society by George IV in 1825 was to Dalton ‘for his development of the chemical theory of Definite Proportions, usually called the Atomic Theory, and other discoveries.’ In his presidential discourse on the occasion, 30 Nov. 1826, Davy placed his services to chemistry on a par with those of Kepler to astronomy. Among his other distinctions was membership (from 1834) of the Royal Society of Edinburgh, of the Berlin and Munich Academies of Science, and of the Natural History Society of Moscow. One of the most gratifying events of his life was a visit to Paris in the summer of 1822. He dined with Laplace at Arcueil in company with Berthollet, Biot, Arago, and Fourier; Gay-Lussac and Humboldt called upon him; Biot presented him at the Institute; he visited Ampère's laboratory; Cuvier did the honours of the museum to him. The pleasurable impression was never effaced.
A proposal made to him by Davy in 1818 to accompany Sir John Ross's polar expedition in a scientific capacity was declined, as well as the generous offer by Mr. Strutt of Derby of a home and laboratory, with a salary of 400l. a year and the free disposal of his time. Attachment to routine probably induced the refusal of the first, love of independence of the second. Yet the monotony of his toil led to a certain stagnation in his ideas. He discouraged reading both by precept and example. ‘I could carry all the books I have ever read on my back,’ he used to say. Narrowness and rigidity of mind were the result. What he had not himself discovered was to him almost non-existent. This unprogressiveness was strikingly manifest in the second volume of his ‘New System of Chemical Philosophy,’ published in 1827. It was a book evidently behind its time. The printing had been begun in 1817, and nearly completed in 1821; the author's experimental results being then added as obtained during six more years. They related to the metallic oxides, sulphurets, phosphorets, and alloys. Many of his old atomic weights were retained in his ‘reformed table;’ he showed himself scarcely disabused of his early prejudices concerning chlorine, sodium, and potassium; gave no sign of adhesion to the law of volumes; and continued to the end of his life to employ his own atomic symbols, completely superseded as they had been by those of Berzelius. To Dulong and Petit's researches on heat he was more respectful. Indeed their law of specific heats, enunciated in 1819, had been in part anticipated by his statement in 1808, that ‘the quantity of heat belonging to the ultimate particles of all elastic fluids must be the same under the same pressure and temperature’ (New System, i. 70).
In 1832 and 1834 honorary degrees of D.C.L. and LL.D. were conferred upon Dalton by the universities of Oxford and Edinburgh respectively. He constantly attended the meetings of the British Association, acting as vice-president of the chemical section at Dublin in 1835, and at Bristol in 1836. In 1834 his friends employed Chantrey to execute a marble statue of him; and while the necessary sittings were in progress in London, Babbage persuaded him to allow himself to be presented at court. As a quaker he could not wear a sword; so he went attired in his scarlet doctor's robes, with the less scruple on the score of their brilliancy that to his own eyes they were undistinguishable in hue from grass or mud.
Meanwhile Babbage, Chalmers, and other well-wishers were anxious to see him relieved from the drudgery of teaching; and the success of their efforts to procure him a pension was formally announced by Professor Sedgwick at the Cambridge meeting of the British Association in 1833. From 150l. a year it was increased to 300l. in 1836, while the devolution upon him, by the death of his brother in 1834, of the paternal estate augmented by purchase, raised him to comparative wealth. He did not therefore relax his industry. He sent to the Royal Society in 1839 an essay ‘On the Phosphates and Arseniates,’ which proved too feeble and obscure to be inserted in the ‘Philosophical Transactions.’ Deeply mortified, he had it printed separately, adding to the note intimating its rejection the remark, ‘Cavendish, Davy, Wollaston are no more.’ Two of four short papers collectively published in 1842, ‘On a new and easy Method of Analysing Sugar,’ and ‘On the Quantities of Acids, Bases, and Water in the different Varieties of Salts,’ announced the discovery, prosecuted by Playfair and Joule, that certain salts rendered anhydrous by heat add nothing to the volume of the water they are dissolved in, the solid matter ‘entering into the pores’ of the liquid.
The Johns family left Manchester in 1830, and Dalton thenceforth lived alone. His friend, Mr. Peter Clare, however, attended him devotedly during his last years of infirmity. On 18 April 1837 he had a shock of paralysis, which recurred in the following year, and left him with broken powers. Impaired utterance hindered him from assuming the office, otherwise designated for him, of president of the British Association at Manchester in 1842. He had another slight fit 20 May 1844, and made a last feeble record of the state of the barometer on 26 July. On the following morning he fell from his bed in attempting to rise, and was found lifeless on the floor. He was in his seventy-eighth year. His remains, placed in the town hall, and there visited, during four days, by above forty thousand persons, were escorted 12 Aug. by a procession of nearly one hundred carriages to Ardwick cemetery. His memory was fittingly honoured by the foundation of two chemical and two mathematical scholarships in connection with Owens College.
Several portraits of Dalton exist. One painted by Allen in 1814 adorns the rooms of the Manchester Philosophical Society. An engraving from it is prefixed to Dr. Angus Smith's ‘Memoir.’ Another by Phillips showing the advance of age belonged to Mr. Duckworth of Beechwood. Chantrey's fine statue stands in the entrance hall of the Manchester Royal Institution. A bronze copy of it was placed after his death in front of the Royal Infirmary. Dalton was always unexceptionably dressed in quaker costume—knee-breeches, dark-grey stockings, and buckled shoes. His broad-brim beaver was of the finest quality, his white neckcloth spotless, his cane gold or silver headed. The members of the British Association were forcibly struck at Cambridge in 1833 with his likeness to Roubiliac's statue of Newton. In society he was unattractive and uncouth, sometimes presenting to strangers the appearance of moroseness. Importunate questionings about his discoveries he was wont to cut short with the reply: ‘I have written a book on that subject, and if thou wishest to inform thyself about the matter, thou canst buy my book for 3s. 6d.’ (Lonsdale, John Dalton, p. 255). Yet he was fundamentally gentle and humane. Those who saw most of him loved him best, and his friendship, once bestowed, was inalienable. He had a high respect for female intelligence, paid to women an almost chivalrous regard, and honoured some with a warm attachment. He was alive to the beauties of nature, enjoyed simple music, and in his youth wrote indifferent poetry. His kindliness and love of truth are exemplified in the following anecdote: ‘A student who had missed one lecture of a course applied to him for a certificate of full attendance. Dalton at first declined to give it; but after thinking a little replied, “If thou wilt come to-morrow, I will go over the lecture thou hast missed”’ (Brit. Quart. Review, i. 197).
Like Newton and Buffon, Dalton disbelieved in what is called ‘genius,’ attributing its results to the determined pursuit of some one attainable object. The processes of his own mind were slow and difficult. He formed his ideas laboriously, and held them tenaciously. An extraordinary sagacity enabled him to reason accurately from frequently defective data. He was a coarse experimenter, and his apparatus (preserved by the Manchester Philosophical Society) was of the rudest and cheapest description. Yet his experiments were so carefully devised as usually to prove a guide to truth. As a teacher he was uncommunicative, as a writer dogged and matter-of-fact, as a lecturer ungainly and inelegant; his true greatness was as a philosophical investigator of the physical laws governing the mutual relations of the ultimate particles of matter.
Complete lists of Dalton's numerous contributions to scientific collections are included in Dr. Angus Smith's and Dr. Lonsdale's ‘Memoirs’ of him. Before the Manchester Society alone he read no less than 116 papers, many of them of epochal importance. In that entitled ‘Remarks tending to facilitate the Analysis of Spring and Mineral Waters,’ communicated 18 March 1814 (Manch. Memoirs, iii. 59), he explained the principles of volumetric analysis, a method of great value to practical chemists. He published in 1801 (2nd ed. 1803) ‘Elements of English Grammar,’ and wrote the article ‘Meteorology’ in Rees's ‘Cyclopædia.’ A German translation of his ‘New System of Chemical Philosophy’ appeared 1812–13, and a second edition of the first part of vol. i. at London in 1842. The second part of the second volume, by which the work was designed to have been completed, was never written.[Dr. Angus Smith's Memoir of Dr. Dalton, and Hist. of the Atomic Theory, forming vol. xiii. ser. ii. of Memoirs of Lit. and Phil. Soc. of Manchester, London, 1856; Dr. William C. Henry's Memoirs of the Life and Scientific Researches of John Dalton, printed for the Cavendish Society, London, 1854; Lonsdale's Worthies of Cumberland: John Dalton, London, 1874; Wheeler's Hist. of Manchester, p. 498; Thomson on Daltonian Theory, Annals of Philosophy, ii. 1813, Hist. of Chemistry, ii. 285; Whewell's Hist. of Inductive Sciences, vols. ii. and iii.; Daubeny's Introduction to the Atomic Theory, 2nd ed. Oxford, 1850; Sir H. Roscoe on Dalton's first Table of Atomic Weights, Nature, xi. 52; North Brit. Review, xxvii. 465 (Brewster); Brit. Quart. Review, i. 157 (Dr. G. Wilson); Quart. Review, xcvi. 43; Roy. Soc.'s Cat. Scientific Papers.]