SKETCH OF ALESSANDRO VOLT A. 119 



of 1782. By means of this apparatus, according to M. Biot, the 

 smallest quantities of electricity, emanating from a source that 

 can reproduce them constantly as they are taken away, were fixed 

 and accumulated in a conductive plate by virtue of the mo- 

 mentary attraction of electricity of a different denomination, 

 from which they were withdrawn when it was desired to make 

 them perceptible and to subject them to observation. During 

 this time Volta was still trying to find signs of electricity during 

 the processes of evaporation and boiling and changes of tempera- 

 ture ; and he finally thought he had discovered electrical effects 

 during the evaporation of water in the phenomena which are 

 now attributed to the friction of the vapor. These results sug- 

 gested the closer examination of the phenomena of atmospheric 

 electricity, concerning which Meteorologia Elettrica he wrote a 

 number of letters to Lichtenberg. Two of his letters related to 

 electrical measurements and the straw electrometer, in which the 

 angle of divergence of two electrified straws was measured. He 

 also, according to Prof. Schuster, constructed the first absolute 

 electrometer, and compared his other instruments with it, so that 

 it would be possible now to refer all his measurements to absolute 

 units. His electrometer consisted of a balance, one pane of which 

 was a flat round disk. Below this disk was placed a large parallel 

 plate, conducted away to earth, while stops were arranged so that 

 the disk could not approach nearer than within two inches of the 

 plate. In the unelectrified state the balance was in a condition of 

 equilibrium. When the disk was electrified, it was attracted 

 toward the plate, but kept at its proper distance by the stops; 

 weights were then added in the other plate of the balance until 

 the disk was pulled away from the stops. The letters also con- 

 tain discussions on the action of points and flames in discharging 

 electricity. To Volta are further owing the invention of the elec- 

 tric eudiometer and of the inflammable air or hydrogen lamp. 

 Prof. Schuster regards as worthy of mention also Volta's investi- 

 gations on gas analysis and his paper on the expansion of gases 

 by heat. He showed the causes which had led different experi- 

 menters to inconsistent results, and established independently 

 what is now known as the law of Charles. 



Volta's crowning discovery of the voltaic pile grew out of 

 researches which were suggested by Galvani's famous experiment 

 with the frog. Galvani attributed the phenomena which he 

 observed in the frog's muscle to a new kind of electricity, which 

 he called animal electricity. Volta, following up his experi- 

 ments with more accurate instruments and by a more careful 

 method, came to a different conclusion. He noticed that the con- 

 vulsions of the frog's muscle were very rarely produced when a 

 single metal was used, and then only under conditions of extreme 



