PHYSIOLOGICAL PHYSICS. 



[Chap. II. 



particles from one place to another. These are simply 

 ways of representing to the mind what is yet not 

 thoroughly understood, and what, in the present state 

 of our knowledge regarding electricity, would not 

 without them be readily understood. 



Voltaic pile. Up to the year 1800 there was no 

 method, apart from friction, for the 

 development of el ectricity . In 1 7 9 1 

 Galvani of Bologna had announced 

 his theory of animal electricity, based 

 on his discovery that when, by means 

 of a metallic arc made half of copper 

 and half of zinc, a circuit was esta- 

 blished between the lumbar nerves of 

 a newly killed frog and the crural 

 muscles, contraction of the muscles 

 resulted. Volta of Pa via rejected 

 Galvam's explanation, and asserted 

 the contractions to be caused by 

 stimulation, due to the development 

 of electricity by contact of dissimilar 

 metals, the moist tissues of the frog- 

 affording merely a means of com- 

 pleting the circuit. In proof of his 

 view Volta constructed the VOLTAIC 

 PILE (Fig. 7). It is formed of a 

 series of discs of copper and zinc, 

 supported on an insulating column 

 of glass. The lowest disc is of 

 copper, above it is a disc of zinc, 

 then a disc of cloth moistened with 

 acidulated water or salt solution. 

 Fig. 7, Voltaic Pile. Following in the same order are 



alternate discs of copper and zinc, 

 succeeded by the layer of moist cloth, to any number 

 that pleases, the topmost disc being of zinc in contact 

 with a disc of copper. The whole pillar is supported 



