Biographical Memoir of Sir John Leslie. 9 



name had attained a high degree of celebrity, he, like most of 

 the other sons of genius, was made to feel that fame brings wth 

 it pains as well as pleasures ; for it was now rumoured that the 

 Differential Thermometer, instead of being an invention of his 

 own,— perfected, as he has himself recorded, in the course of a 

 series of experiments on the evaporation of ice, which the se- 

 vere winter of 1794-5 afforded him an opportunity of perform- 



jno-,* was in reality a plagiarism, if not from Van Helraont, 



who died in 1644, at any rate, from John Christopher Sturmius, 

 who died some sixty years later. Such was one attempt to im- 

 peach the originality of this eminently inventive experimental- 

 ist. An instrument, of which all the world remained ignorant, 

 till he, by means of it, told the world the better part of all it 

 yet knows concerning the phenomena of radiated heat, was dis- 

 covered to have been furtively purloined from one or other of 

 these antiquated worthies ! Neither the authors nor the abet- 

 tors of this allegation pretended that either Van Helmont or 

 Sturmius ever dreamt of such applications, or derived such re- 

 sults from their supposed invention, as were reserved, by some 

 caprice of chance, no doubt ! for its luckier plagiarist ; and it is, 

 we believe, generally admitted, that this is just one of those 

 cases of curious but partial anticipation so frequently to be met 

 with in the history of science ; and where the ultimate inventor 

 shews, by his skilful and fruitful employment of the disputed 

 invention, how much he surpassed, and hoAv little he needed the 

 help of those whom he is ungenerously supposed to have robbed 

 (}f their legitimate honours. 



In the spring of 1796, Mr Leslie received' an invitation from 

 his friend Mr Thomas Wedgwood, to accompany him in a tour 

 through the north of Germany and Switzerland. To this pro- 

 posal, whicli was everyway agreeable, he immediately acceded. 

 They arrived at Hamburg about the first of May, and employ- 

 ed that and the next four months in their tour, part of which was 

 performed on foot. He alludes to some observations which they 

 made in the course of their journeyings amongst the mountains of 

 Switzerland, in one of the notes to his celebrated work on Heat ; 

 but of this, as of all his subsequent tours on the Continent, he 



• See the article Jleteorology in the Encyclopaidia. 



