400 WELLS'S NATURAL PHILOSOPHY. 



What was de- '^^® experiments of Galvani were repeated by Volta, an 

 termired by eminent Italian philosoplier, wlio found tliat no electrical or 

 ^°'''*^ nervous excitement took place unless a communication be- 



tween the muscles and the nerves was made by two different metals, as cop- 

 per and iron, or copper and zinc. He considered that electricity was produced 

 by simple contact of the dissimilar metals, positive electricity being evolved from 

 the one and negative electricity from the other. 



What is the The true cause of electrical excitement occa- 

 ^^^ctridtTde- sioned by the contact of dissimilar metals is 

 uct^of ''differ! iiovv fuIly ascertained to be chemical ac- 

 ent metals? tion ; and recent researches have also proved 

 that no chemical action ever takes place without the de- 

 velopment of free electricity. 



The electricity produced by chemical action has been 

 termed Galvanic, or Voltaic Electricity, in honor of Gal- 

 vani and Volta, who first developed its phenomena. 

 How does sal- 772. Galvanic electricity, or the electricity 

 fr*o"m ordfnfry dcvclopcd by chcmical action, differs from fric- 

 eiectricity? tioual, Or Ordinary electricity, chiefly in its 

 continuance of action. The electricity developed by fric- 

 tion from a glass plate, or the cylinder of an electrical 

 machine, exhibits itself in sudden and intermittent shocks, 

 accompanied with a sort of explosion ; whereas that which 

 is generated by chemical action is a steady, flowing current. 



The fundamental priuciplo which forms the basis of the science of galvanic 

 electricity is as follows : 



Any two metals, or more generally, any two 

 forms the basis different bodlcs which are conductors of elec- 

 of gaivamc trlcity, whcu placed in contact, develop elec- 

 e ec nci y . tricity by chemical action — positive electricity 

 flowing from the metal which is acted upon most power- 

 fully, and negative electricity from the other. 



In general, that metal which is acted upon 



What are elec- ° ., . . . ^ . 



tro-positive most easilv is termed the electro-positive metal, 



and electro- , "^ iiji ii 



negative eie- 01 element ; and the other the electro-nega- 

 tive metal, or element. 

 The electrical force or power generated in this way is 

 called the electro-motive force. 



