^0 Biographical Memoir of Horace Benedict de Saussure 



which instructed him in lithology, and the principal documents 

 from which he derived his ideas respecting the history of the 

 earth. The environs of that city were covered with rolled 

 stones, frequently even with great masses of very diversified sub- 

 stances, foreign to the neighbouring mountains, and which are 

 found in situ only in the high Alps. These masses became to 

 Saussure a rich cabinet of mmeralogy, and indicated to him the 

 violent revolutions which had conveyed their materials to such a 

 distance from their original positions. 



To be perfectly convinced, however, of the existence of these an- 

 cient revolutions, it was necessary to prove that the causes at pre- 

 sent in operation are incapable of producing such effects; and, for 

 this purpose, he required to measure each of these causes, and to 

 appreciate the extent of their influence. He had, therefore, to 

 examine attentively the lake, and the rivers which empty them- 

 selves into it, and which descend from the glaciers ; to determine 

 the velocity and direction of their motions, their temperature, 

 and the quantity and quality of the substances which they carry 

 along with them : he had to employ, and even invent, instru- 

 ments of a delicacy proportionate to the measurements which he 

 had in view to obtain. But these running streams are the pro- 

 ducts of rains, and the melting of the glaciers, which last are 

 themselves incessantly renewed by the snows which the clouds 

 deposite in these high regions. It was therefore necessary to deter- 

 mine the quantity of these various sources, to ascend even to the 

 cause of rain, the most important and difficult to explain of all 

 the meteors ; and as the most probable origin that can be as- 

 signed, is to suppose it to be formed from the vapours of the 

 atmosphere, it was still farther necessary to explore all the means 

 of appreciating the quantity and nature of these vapours in all 

 circumstances. 



It was by following out this train of ideas, joined to the de- 

 sire of precision which always distinguished him, that Saussure 

 was led to improve the thermometer, for measuring the tempera- 

 ture of water at all depths ; the hygrometer, for indicating the 

 greater or less abundance of watery vapours ; the eudiometer, 

 for determining the purity of the air, and for finding out whe- 

 ther or not there might be any other cause of rain than in the at- 

 mospheric vapours ; the electrometer, for ascertaining the state of 

 electricity, which operates so powerfully on the aqueous me- 



