CHAP. VI., 5.] 



HEAT. SIR JOHN LESLIE PICTET. 



145 



published it more than thirty years after, when cer- 

 tainly 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 evi- 

 dence 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, in- 

 genious, if not close reasoning, considerable inven- 

 tiveness in imagining experiments and in constructing 

 apparatus, and a general tendency to express physi- 

 cal laws in a mathematical form. It must be con- 

 fessed, that these merits were united to a good deal 

 of dogmatism, and a somewhat supercilious judgment 

 of persons eminent in science whose years and at- 

 tainments 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 So- 

 ciety 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 con- 

 nection 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 Wedg- 

 wood. 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 medi- 

 tated 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 cir- 

 cumstances with foreign philosophers, and the fami- 

 liarity gained with their language and experiments, 

 contributes to it in no small degree. 



We have now come to the period of Mr Leslie's 

 ]}f e w h en hj s character and position became esta- 

 blished, the first by the publication of his Experi- 

 mental Inquiry into the Nature and Propagation of 



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 cha- 

 racter as a mathematician. 



Mathematics were, as has been stated, his earliest (646.) 

 pursuit, and he cultivated them with great industry Mathemati- 

 and success. His adviser, Plavfair, was attached ? al wnt " 



ID CTS 



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 pre- 

 fers demonstrations, whether in mathematics or na- 

 tural 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 know- 

 ledge, and is justly commended by Chasles and other 

 foreign writers. His attempt to replace Euclid's Ele- 

 ments by a new work on Elementary Geometry was 

 not more successful than such attempts have usually 

 been. 



Unquestionably, the bent of Leslie's mind was ( 64 ?-) 

 to physical research, in which he showed a peculiar importance 

 talent ; and his selection of Heat was, as we have of the sub- 

 hinted, well - timed ; since there appeared a con- J ect f ra - 

 vergence of attention to the subject, such as usually heat ' 

 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 con- 

 centration of cold by a concave mirror. As this ex- 

 periment really opened anew the subject of radiant 

 heat, we shall dwell for a moment on Pictet's labours 

 and their results. 



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 man- 

 ners and great information, was known and esteemed 

 by the learned throughout Europe. He was the 

 author of numberless papers in a scientific jour- 

 nal which he edited ; but his work on fire Essai sur 

 le Feu published in 1791, was his principal pub- 

 lication. It contains some good observations on latent 

 and specific heat ; and on the power of different kinds 



