ter

(628.)

early as 1816, elected a corresponding member of the Institute of France-Wollaston being then probably the only other English name on the list.1 Dalton found his way to Paris in 1822, and was agreeably surprised by the distinction with which he was received by the most eminent members of the Academy of Sciences. Perhaps this first personal recognition of his exalted station, as a man of science, had something to do with the tardy adjudication to him four years later of one of the medals of the Royal Society of London. In 1830 he was elected one of the eight associates of the Academy of Sciences in the room of Sir Humphry Davy.

In 1833, at the age of sixty-seven, he received a His charac- pension from government, up to which time he had maintained himself in the way already mentioned, with the utmost simplicity and contentment. Even in his lifetime it was impossible for his eulogists to forbear from some reference to this essential part of his really philosophic character. "Mr Dalton has been labouring," says Sir Humphry Davy, "for more than a quarter of a century with the most disinterested views. With the greatest modesty and simplicity of character, he has remained in the obscurity of the country, neither asking for approbation, nor offering himself as an object of applause." "There is little doubt," says Dr Thomson, "that Mr Dalton, had he so chosen it, might, in point of pecuniary circumstances, have exhibited a much more brilliant figure. But he has displayed a much more noble mind by the career which he has chosen; equally regardless of riches as the most celebrated sages of antiquity, and as much respected and beloved by his friends, even in the rich commercial town of Manchester, as if he were one of the greatest and most influential men in the country." All who had the good fortune to know him personally-to see him, as the writer of these pages has done, in his modest school-room, and surrounded by his unpretending apparatus-will own that these eulogies are and death. not overdrawn. His latter days were spent in cheerfulness and comfort; he expired on 27th July 1844, having nearly completed his seventy-eighth year.

ter.

(629.)

The philosophical character of Dalton may be Dalton's briefly summed up. He had immense vigour of conphilosophical charac- ception, and an ardent love of truth. He was thoroughly devoted to the pursuit of science during his long career, and he evidently sought and expected no higher reward than the insight which he obtained into the laws of nature. His mind, like his frame, was of a strongly masculine character, and happily exempt from nervous sensibility and other like infirmities of genius. Whilst he held his own opinions with tenacity, and criticised freely those of his opponents, there is not a trace of acrimony in any

of his writings; and he always spoke in terms of high respect both of those who pursued science in a similar direction with himself, and (what was more difficult) likewise of those who, having the good fortune to hold more conspicuous positions, showed him the smallest degree of kindness, which he always gratefully acknowledged. He was unlike Black and Cavendish, in the rapidity with which he seized on a few isolated facts, and made them the basis of an inference of great generality; this, indeed, was his leading characteristic; and he differed from them equally in the boldness with which he claimed from the public a general acceptance of his conclusions. Some of his inferences were unguarded enough, and have not been confirmed; and the reception of what were correct was naturally delayed by the evident facility with which his theories were shaped in his own mind. Most of his papers appeared in rapid succession; only the Atomic Theory was brought with some evident hesitation before the world. In all this we see the results of a vigorous imagination, united with great perseverance, in working out an idea. The imaginative element would have been more under control had his education been of a less

irregular kind. We see the effect of an opposite turn in his eminent predecessors just named. They would have done more, had they trusted more. Dalton's discoveries may be said to have terminated at the age of forty. Though he laboured for thirty years after, the conceptive faculty seems to have spent itself in its earlier efforts.

JOSEPH LOUIS GAY-LUSSAC, an eminent French (630.) chemist and physicist, contemporary with Dalton, Gay-Lushas been mentioned in the course of the present sec-sac-che tion, as having discovered independently the equal mist and dilatation of the gases, and also a law of their combinations in connection with their volumes, which was peculiar to himself. Besides these researches, science owes many useful observations in physics to his energy and talent, which, in the origin of his career, promised more of originality than his maturer life perfectly fulfilled. He was born in the old province of Limousin in 1778, and became the pupil of Berthollet in chemical researches, and was one of the earliest and most active members of the Société d'Arceuil. In physics, he was the collaborator of MM. Biot, Humboldt, and Laplace. With the first Remarkof these philosophers he made his earliest experi-able balment in aërostation, which he repeated alone on the loon ascent. 16th September 1804, when he attained the amazing height of 7016 mètres (23,019 English feet), an elevation previously unattained, and which in the course of the succeeding half century has only twice been touched, or exceeded by a small quantity.2 Con

(631.)

(632.)

Thomson, Count of

sidering the novelty of the experiment in 1804 (only twenty-one years after Montgolfier's first successful experiment), this fact speaks strongly for his courage and zeal. These ascents were also the first undertaken with strictly scientific aims, and the observations made were highly interesting in connection with the decrement of temperature in the atmosphere, with the uniformity of composition of air at all heights, and with the question of whether the magnetic force of the earth diminishes at such elevations. This last enquiry was not conclusively answered.

With M. de Humboldt he made observations on

terrestrial magnetism in Italy, and on other subjects. MiscellaBy desire of Laplace he studied the facts of capillary neous exattraction. In more immediate connection with the periments of Guysubject of the present chapter, he made some valu- Lussac. able experiments on hygrometry, on the mechanical properties of vapour of different kinds, and on the specific heat of the gases. His fame, however, mainly rests on the two investigations to which we previously referred, and on the results of his balloon journey. His later years were devoted to practical enquiries connected with chemistry, and to his official duties at the Mint. He died at Paris on the 9th May 1850. His death.

THE name of Thomson, Count of Rumford, deserves a passing notice in the history of the physiRumford. cal sciences, if not for the absolute importance of his discoveries, at least as an instance of a class of benefactors to mankind at once in a physical and intellectual point of view. He was altogether in advance of his age in the application of correct theory to the improvement of the social condition of the lowest classes; and many of his experiments, and, indeed, discoveries, seem now at once so simple and so familiar, that we are apt to forget how entirely original they were sixty years since.

(633.) Sir BENJAMIN THOMSON, an American by birth, a His early British knight, and a Bavarian or rather Austrian history and studies. count, was born in the United States in 1753, and passed his earlier years almost entirely at military stations during the American war, being engaged on the British side. After the establishment of independence, he quitted his country for ever; came first to England, where he was well received, and proposing to enter the Austrian service, he proceeded as far as Munich, where, having become known to the elector of Bavaria, he was induced to settle; and having received different civil and military appointments, he devoted himself for a series of years to the improvement of the social condition of that capital. He introduced great improvements into the management of the army; the mechanical and chemical departments of the artillery had a peculiar charm for him; they were conducted on strictly scientific principles, and, in return, were made to contribute important results to science. His experiments on the heat of friction, deduced from the boring of cannon, are amongst the best we possess; and they led him to results of considerable theoretical importance to which I shall presently refer.

(634.) Enquiries

But his most serviceable efforts on behalf of maninto the kind were in the treatment of the mendicant classes

economical

applica

tions of

heat.

The

with which Munich then swarmed. Salutary views
of the importance of industry, order, morality, and
public economy, were most happily united to a
happy versatility of talent in physical research, to
unwearied patience and great liberality, in effecting
one of the greatest social reforms on record.
strict statistics of a great house of industry were
ascertained with reference to the most seemingly in-
significant details, and, in particular, all the appli-
cations of Heat to the physical wants of mankind
were studied with equal assiduity and success. The
warmth of clothing was traced to the amount of still
air entangled amongst its fibres,-the dissipation of
heat, whether from a thermometer or a kitchen boiler,
was classified under radiation, conduction, and con-
vection, the last and often most important of which
(signifying the influence of currents in liquids and
gases in conveying heat by the changing density of
their parts) had hardly before been recognised, or at
least made the subject of formal experiment,—the
effective heat due to the combustion of different kinds
of fuel, tested by a calorimeter of his own invention,

the economy of light based on an investigation of the properties of flame;-these were but a few of the trains of enquiry, of which his Mendicity House was the primary object. Charity and science went Practical hand in hand; and when we award to Watt the benefits rehighest honours for an invention which enabled him sulting. to create mechanical force at an economy of twothirds of the coal previously consumed, shall we deny Rumford a civic crown for having so improved the methods of heating apartments and of cooking food, as to produce a saving in the precious element of heat, varying from one-half to seven-eighths of the fuel previously consumed? When we consider the enormous price of wood in nearly every part of the Continent, the destruction of forests which has occurred, and the consequent injury to the climate, as

(635.) Different experi

ments.

well as to the material wealth of many districts, we are disposed to give Rumford a higher place than has generally been accorded to him. Had his excellent principles been universally carried out, some millions sterling would have been saved to every large state in Europe. Fontenelle characteristically says of a certain savant, who made experiments on nutrition, with a view to carry fasting to the utmost practicable extent, that his researches had the double aim of a place in heaven and in the academy. Cuvier, who tells the anecdote in his Eloge of Rumford, adds, that the latter had a truer claim to the questionable compliment. That science is surely not despicable by which a pound of wool, of fuel, or of food, can be made to go one-half farther than before in warming the naked and in feeding the hungry.

All Rumford's experiments were made with admirable precision, and recorded with elaborate fidelity, and in the plainest language. Everything with him was reduced to weight and measure, and no pains were spared to attain the best results. His experiments on heat, and the properties of bodies in connection with it, are the most important. He first applied steam generally in warming fluids and to the culinary art. He maintained the paradox of the non-conducting power of liquids, which, though practically true, appears not to be rigorously so. He contrived many ingenious instruments; but his thermoscope, identical with Leslie's differential thermometer, was probably of later invention, if not in some measure borrowed from it. In like manner his proofs of the maximum density point of water were unquestionably suggested by Dr Hope's beautiful experiment, although this derives its meaning from the laws of convection, which Rumford first established. That water expands in bulk below the temperature Dr Hope on of 39° or 40° Fahr. until it freezes, is a fact which the maxi- had been asserted since the middle of the seventeenth sity point century. But for 150 years its great improbability, and the unquestionable uncertainty introduced into the result by the irregular expansion of the containing vessel or glass of the thermometer, enabled sceptics in every generation to withhold their assent. Perhaps the last who doubted was the illustrious Dalton. He allowed himself however to be convinced by Dr Hope's experiment, in which the temperature of the denser and rarer water is measured by two thermometers placed at the bottom and top of a cylindrical jar, and nothing interferes with the natural tendency of a fluid to arrange its particles according to their specific gravity, the lighter resting on the heavier ones. It is to be regretted that Hope did not prosecute original enquiry, for which the conception of this experiment, and the mode in which he conducted

(636.)

mum den

of water.

1 Edinburgh Transactions, vol. v.

it,' show that he had excellent qualifications. Hope
was first the colleague, then the successor of Black
in the chair of chemistry in Edinburgh; and in his
time probably the most popular teacher in Europe
of that science. He died on the 13th June 1844,
in the
in the seventy-eighth year of his age.

Rumford's name will be ever connected with the (637.) Rumford progress of science in England by two circumstances; Prize-the first, by the foundation of a perpetual medal and Royal Inprize, in the gift of the Council of the Royal Society stitution. of London, for the reward of discoveries connected with Heat and Light; and secondly, by the establishment, in 1800, of the Royal Institution in London, destined, primarily, for the promotion of original discovery, and, secondarily, for the diffusion of a taste for science amongst the educated classes. The plan was conceived with the sagacity which characterized Rumford, and its success has been greater than could have been anticipated. Davy was there brought into notice by Rumford himself, and furnished with the means of prosecuting his admirable experiments. He and Mr Faraday have given to that institution its just celebrity with little intermission for half a century.

last years and death.

Rumford spent his later years in Paris, where he (638.) died in 1814. The estimation in which he was then Rumford's held may be judged of from the fact, that he was one of the eight foreign associates of the Academy of Sciences. He was very capable of having done more for science: the versatility of his talents, the accidents of his early life, and the strong hold which principles of philanthropy and public utility always exerted over him, account for the absence of more sustained and erudite researches. But in those very particulars he deserves to be cited as a practical philosopher, as to many things in advance of his age, and a benefactor both to science and to mankind."

(639.) His opinions on the nature

In the history of pure science Rumford will be chiefly remembered by his espousing the (not new) theory that heat consists in a motion of some kind amongst the particles of matter, in opposition to the of heat imopinions then so prevalent amongst chemists, which portant. almost tended to regard it as an element capable of forming combinations. Rumford's view was mainly Derived based on the facts of friction, which he showed to be from expeirreconcilable with the notion of a change in the spe- friction. cific heat of the abraded matter, and to be seemingly inexhaustible so long as the force producing friction is continued. His conclusion was, that the heat then generated cannot be a substance, but an affection of body of the nature of vibratory motion. The amount of heat evolved in boring cannon is very

riments on

(644.) Travels.

published it more than thirty years after, when certainly it was not calculated to advance science in a perceptible degree. An essay on Heat and Climate, read at the meetings of the Royal Society of London in 1793, had not a more favourable reception; and though published twenty-six years later in Thomson's Annals, it was refused a place in the Philosophical Transactions. The author, no doubt, attributed these rejections to the boldness with which he criticised opinions currently received, and to the novelty of the views which were shadowed forth; but something is, no doubt, to be allowed for the real immaturity of these works, the involved and even inflated style in which they were written, and the questionable evidence for some of the conclusions. In these, and in some subsequent scattered papers in Nicholson's Journal, we observe, with all the faults, yet many of the merits of those researches which afterwards made him justly famous. We find acute observation, ingenious, if not close reasoning, considerable inventiveness in imagining experiments and in constructing apparatus, and a general tendency to express physical laws in a mathematical form. It must be confessed, that these merits were united to a good deal of dogmatism, and a somewhat supercilious judgment of persons eminent in science whose years and attainments should have commanded respect. This, however, is a fault which many ardent students not very conversant with the world have had abundant occasions to regret at leisure. Whether or not he believed Sir William Herschel to have had some share in the refusal of his paper by the Royal Society I do not know, but it is difficult, on other grounds, to understand the bitterness with which he expressed himself as to that eminent person, in connection with his experiments on heat.

One of the circumstances which most contributed to encourage Mr Leslie's taste for experiment, was his engagement for above two years as tutor and companion in the family of the ingenious Mr Wedgwood. Another was the opportunities which he found or made for himself of foreign travel. With or without companions he visited, in the early period of his career, America, and most of the northern countries of Europe, particularly Holland, Germany, Switzerland, Sweden, and Norway. He also meditated a journey to Egypt and the East, a project reluctantly abandoned, and to which he reverted even in the last years of his life; but it was never carried into effect. Nothing, perhaps, fosters so surely a taste for science as such extended tours; and the acquaintance made under the most agreeable circumstances with foreign philosophers, and the familiarity gained with their language and experiments, contributes to it in no small degree.

(645.) We have now come to the period of Mr Leslie's Publishes life when his character and position became established, the first by the publication of his Experimental Inquiry into the Nature and Propagation of

his Essay

on Heat.

Heat, in 1804; the latter by his appointment to the chair of mathematics in the University of Edinburgh in 1805. I shall first say a few words on his character as a mathematician.

cal writ

Mathematics were, as has been stated, his earliest (646.) pursuit, and he cultivated them with great industry Mathemati and success. His adviser, Playfair, was attached ings. to the methods of the foreign mathematicians; and Leslie no doubt acquired from him, as well as from his continental friends, a taste for the notation of Leibnitz, then hardly employed in this country, but which he uses in his work on Heat, and elsewhere. Nevertheless, his real preference appears to have been decidedly geometric. He almost always prefers demonstrations, whether in mathematics or natural philosophy, in the manner of Huygens and Newton. He could hardly be called a discoverer in mathematics; but his work on Geometrical Analysis and the Higher Curves shows much taste and knowledge, and is justly commended by Chasles and other foreign writers. His attempt to replace Euclid's Elements by a new work on Elementary Geometry was not more successful than such attempts have usually been.

diant heat.

Unquestionably, the bent of Leslie's mind was (647.) Growing to physical research, in which he showed a peculiar importance talent; and his selection of Heat was, as we have of the subhinted, well-timed; since there appeared a con- ject of ravergence of attention to the subject, such as usually heralds some eminent discovery. The doctrines of heat in combination, of which we have already spoken, had engaged the attention of Black, Cavendish, and Lavoisier; the subject of meteorology, in which Leslie took the greatest interest, was becoming a science in the hands of De Saussure and Deluc; whilst Pictet repeated (without being aware of the anticipation) the curious observation of Porta on the apparent concentration of cold by a concave mirror. As this experiment really opened anew the subject of radiant heat, we shall dwell for a moment on Pictet's labours and their results.

Pictet of

Geneva.

Geneva was at this time nearly in the zenith of its (648.) reputation as a nursery of the sciences. The most eminent and independent of its citizens were proud of being also amongst its instructors, and the office of professor was then, as it still is, considered one of the most honourable in the state. About 1790 De Saussure, the most eminent physical geographer of his time, was in the vigour of his intellect, and amongst his friends and coadjutors MARC-AUGUSTE PICTET held a conspicuous place. The latter was professor in the Academy, and being a person of popular manners and great information, was known and esteemed by the learned throughout Europe. He was the author of numberless papers in a scientific journal which he edited; but his work on fire-Essai sur le Feu-published in 1791, was his principal publication. It contains some good observations on latent and specific heat; and on the power of different kinds