16 Biographical Memoir of Sir John Leslie. 



the French and German languages. He reproduced it, with 

 considerable emendations, in the second volume of his " Mathe- 

 matical Course," which, besides, contains the Geometry of 

 Curve Lines. This volume was not published till 1821 — 

 an interval of twelve years having thus elapsed from the ap- 

 pearance of the first. A third volume, on Descriptive Geome- 

 try, and the Theory of Solids^ was still wanting to complete his 

 original design ; but his removal to another Chair, and other 

 circumstances, called his attention to different objects, and his 

 " Mathematical Course"" was thus left unfinished. He was in- 

 duced, at a late period of his life, to recast the first volume in 

 a gi'eatly abridged form. His object in doing so was to accom- 

 modate it to the use of those who, in riper years, became desi- 

 rous to supply the defects of early education, and to qualify 

 themselves for obtaining some knowledge of Natural Philoso- 

 phy. This abridgment appeared in 1828, under the title of 

 Rudiments of Plane Geometry, including Geometrical Analysis, 

 and Plane Trigonometry. In connection with his mathemati- 

 cal works, though forming no part of his " Course," we may 

 here mention the profound and learned treatise on the Philoso- 

 phy of Arithmetic, which he published in 1817. It was a re- 

 publication, with considerable alterations and additions, of one 

 of the numerous articles contributed by him to the Supplement 

 to the former editions of this Encyclopjedia. 



It was not to be expected that the labours of the Mathematical 

 Chair would wean Professor Leslie from his favourite experimen- 

 tal inquiries. His fine instruments were always at hand, and 

 always in use, in connection with some ingenious conception or 

 other. Early in the summer of 1810, he determined to pro- 

 ceed with a set of experiments previously suggested in the 

 course of his researches with his Hygrometer, but which had for 

 some time been suspended ; and they now, on being resumed, 

 conducted him to the discovery of that beautiful process of Ar- 

 tificial Congelation, by which he was enabled to produce ice, 

 and even to freeze mercury, at pleasure. The discovery was 

 achieved by means of a happily conceived combination of the 

 powers of rarefaction and absorption, effected by placing a vei'y 

 strong absorbent under the receiver of an air-pump. It was in 

 tlie month of June of that season that the discovery was con- 



