18 Biographical Memoir of Sir John Ledie. 



the capital failed in their trials of it, till it was performed there 

 by himself, in the ensuing summer !* 



In a letter from London to one of his friends, written in 

 June 1811, he says, — " My package has at last arrived, and I 

 shall proceed without delay to make my debut.'"'' It was only 

 now that the experiment was first successfully performed in the 

 capital. This took place in presence of several members of 

 the Royal Society. The discovery was announced in the 

 same year, in the Memoirs of the French Institute ; and 

 the process itself was afterwards exhibited before that body, 

 by M. Pictet and M. Gay-Lussac.+ He did not himself pub- 

 lish any detailed account of his experiments till 1813, when he 

 explained them at considerable length, in a small volume enti- 

 tled, J short Account ofExper'ivicnts and Instruments depending 

 on the Relations of Air to Heat a?id Moisture. This publica- 



• Some equally complete and curious legal evidence of these facts was addu- 

 ced bv Professor Leslie, in 1822, in a prosecution which he was advised to in- 

 stitute against the publisher of a well-known Magassine, for a series of libels 

 inserted in that work; in one of wliich he was accused of having stolen the 

 discovery alluded to from Mr Nairne. Amongst other witnesses, two very dis- 

 tinguished Chemists were examined on that occasion — the late Dr Marcet, 

 and Dr Thomson, Professor of Chemistry in the University of Glasgow. The 

 evidence of both was equally favourable to Professor Leslie. We shall ex- 

 tract a small portion of that of Dr Marcet, to whom the Professor was per. 

 soually but little known : — " Q. Is it your opinion that Mr Leslie is to be 

 considered as having borrowed or stolen this discovery, or do you consider 

 his discovery to be original? — A. Some of the facts were known long be- 

 fore, but the process itself is perfectly original — Q. Is the discovery of Mr 

 Leslie analogous to other discoveries in the science of chemistry ? — A. There 

 is hardly any discovery of the least value that has been made in that science 

 but from the known properties of bodies. It is by combiuuig those proper- 

 ties, so as to produce certain effects, that a discovery is made Q. Then you 



mean to say that Mr Leslie has done what none before him ever accomplish- 

 ed ? — A. Certainly. He has done what the whole philosophic world, icith all 

 the facts be/ore tJietn for a long period, had not been able to accomplish. — Q. 

 "When and by whom was the experiment first successfully performed in Lon- 

 don ? — A. It was successfully performed in London by ]Mr Leslie himself. 

 My belief is, that no one succeeded in this experiment, in London, until Mr 



Leslie himself shewed the wny Q. Do you know that Sir Humphrey Davy 



tried and failed ? — I cannot positively say ; I believe he tried it, but without 

 success." — (Report of the Trial by Jury, Professor Leslie against William Black- 

 -Kood, p. 82-6.) 



t See Mimoires de la Classe des Sciences MatMmatiqites et Physiques, t. xii. 

 p. 80 ;t. xiv. p. 117-18. 



