1 64 GREAT MEN OF SCIENCE 



was his 'electrometer,' consisting of two straws, but this was 

 then superseded by the gold-leaf, and later by the aluminium- 

 leaf electroscope; he used it to make measurements of as- 

 tonishing sensitivity, especially when he added to it the 'con- 

 denser,' which consisted of two metallic plates, separated 

 only by a thin coat of lacquer, acting as an insulator, the 

 result being a Leyden jar of high capacity. When the two 

 metal plates were separated, the voltage to be measured on the 

 electrometer was multiplied one hundred times. All this, as 

 well as his electrophorus, was not fundamentally new, but 

 it indicated a development and mastery of the art of electrical 

 measurement which at that time was something quite new, 

 and shared by no one besides Coulomb. Volta also was the 

 first to measure atmospheric electricity, by connecting his 

 electrometer to an insulated flame. 



The introduction of measurement, of quantitative observa- 

 tion, into the study of electrical phenomena, of which 

 Coulomb had been the pioneer, proved also in Volta's case 

 to be fertile in results of fundamental importance, when he 

 took up work on frog preparations, in common with many 

 other people, immediately after the appearance of Galvani's 

 paper. In the course of eight years his work resulted in the 

 revolutionary discovery of the 'pile,' and the 'cups,' which 

 were marvellous and completely novel apphances for 

 investigating entirely new regions of knowledge. 



First of all, after numerous experiments on frog prepara- 

 tions, which at first were only slight variations on Galvani's, 

 he arrived at the discovery that the muscular contractions are 

 not necessarily conditioned by the transference of electricity 

 from nerve to muscle, but that an electrical stimulus of the 

 nerve alone is sufficient to set the corresponding muscle in 

 motion. He proved this by laying bare a piece of the nerve 

 of the thigh, and providing this with two tinfoil electrodes 

 sufficiently far apart, through which a weak electric dis- 

 charge could be sent along the nerve without passing 



