EULOGY ON ALEXANDER VOLTA. 119 



have discovered so many vestiges, aud which, iiotvvithstiuidiug their 

 vast extent, may leave some chance of safety to a few individuals advan- 

 tageously situated, but from an all-pervading and inevitable cause, in 

 which case the frozen zones of the poles, the burning regions of the 

 equator, the vastness of the ocean, and the snowy summits of the Cor- 

 dilleras and Himalayas would be equally powerless to save. To study 

 all that can be discovered of this great phenomenon up to the present 

 time, to collect all the exact data with which the centuries to come will 

 be teeming-, is the task physicists are hastening to accomplish, especially 

 since the eudiometer with the electric spark has suiiplied them with 

 the means of so doing. To answer some of the objectious to which the 

 tirst trials of this instrument gave rise, Humboldt and Gay-Lussac sub- 

 mitted it to the most scrupulous examination. Wheu such judges 

 declare that no known eudiometer approaches in accuracy that of Volta, 

 doubt as to its value can no longer exist. 



DILATATION OF THE AIR. 



As I have abandoned the chronological order, before taking up the 

 two most important works of our venerable fellow-member, before analyz- 

 ing his researches on atmospheric electricity and describing his dis- 

 covery of the pile, I will mention in a few words the experiments pub- 

 lished by him in 1793 on the subject of the dilatation of air. 



This important question had already attracted the attention of a great 

 number of skillful physicists, who could uot agree either on the total in- 

 crease of volume that air undergoes between the fixed temperatures of 

 melting ice and ebullition, or the rate of the expansions of the interme- 

 diate temperatures. Volta discovered the cause of these discordances. 

 He showed that, by operating in a vessel containing humidity, theincrease 

 of expansion would be found ; that if there be in the apparatus no more 

 humidity than the film ordinarily covering the sides of the glass, the ap- 

 parent expansion of the air will be increasing in the lower part of the ther- 

 mometric scale and decreasing in the upper part. He finally proved, 

 by delicate measurements, that atmospheric air, if confined in a per- 

 fectly dry vessel, expands in proportion to its temperature, when this 

 latter is measured by a mercurial thermometer divided into equal parts. 

 Xow, as D'Huc's and Crawford's works seemed to establish the fact that 

 a similar thermometer gives the correct measurement of the amount of 

 lieat, Volta felt himself authorized to announce, in the new terms, 

 v.hose iniportaricc all will appreciate, the very simple law resulting from 

 his experiments, that the elasticity of a given volume of atmospheric air 

 is in proportion to its heat. 



When air, at a low temperature, and constantly containing the same 

 amount of humidity, was heated, its elastic force increased as did that 

 of dry air. Volta concluded from this that the vapor of water and air 

 expand precisely in the same nuinner. Every one now knows that this 

 result is accurate; but the experiment of the jdiysicist of Como did leave 



