131 



advancement of theory — who have worked for the pure love of 

 science, without any idea of gain to themselves or benefit to the 

 world at large — to whom it has rarely occurred that their labours 

 would bear other fruit than the explanation of a phenomenon, or 

 a separate existence and a name of its own to some substance. 

 Galvani's mind was not engrossed with any immediate benefit he 

 would confer upon mankind when he made his experiments upon 

 the frog's limbs. He was only trying to settle a point in physiology. 

 Whether he found what he was in quest of or not, does not matter, 

 but he found something else. The limbs of the frog were hanging 

 by a nerve from a metal support near an electric machine, and it 

 was observed that the limbs twitched at every spark of the machine. 

 Galvani could turn even this fact to a practical account, for he 

 afterwards used frogs' limbs as electroscopes, and when so doing 

 on one occasion, he observed the same twitchings as before, when 

 the limbs and the metal attached to the nerve touched, at the 

 same time, an iron railing. He explained this phenomenon by 

 asserting that there was electricity in the limb itself Volta main- 

 tained that the electricity was all owing to the contact of two 

 different metals, and some one else attributed such phenomena to 

 chemical action. Hence arose the two rival hypotheses usually 

 called the contact theory and the chemical theory, and the sequel 

 will show how, from mere hypothesis, a great deal of practice may 

 spring, though indirectly. 



These theories led to much discussion and investigation, and 

 to new discoveries, amongst which may be mentioned Volta's pile, 

 Davy's electric light, Oersted's discovery of the action of electricity 

 on the magnetic needle, and Faraday's specific inductive capacity 

 and magneto-electricity. 



"What have all these to do with theory and practice?" it may 

 be asked. The answer is that these discoveries to which Galvani's 

 experiment led are just like so many guide-posts, stretching their 

 arms in many directions — pointing out the way to practical applica- 

 tions of service to the metallurgist, the photographer, and the sugar- 

 refiner — leading up to the electric telegraph and the Atlantic cable 

 — guiding men to the brilliant light which sends its beams far over 



