484 nature's teachings. 



Electricity. Many other substances, such as glass, sealing-wax, 

 &c, possess the same property. 



This frictional electricity is but transient, the electric fluid, 

 if we may be allowed to use the term, being driven out by 

 main force from the material in which it was latent, just as fire 

 is procured by the friction of two dry sticks. There is, how- 

 ever, a form of Electricity called Galvanism, from its discoverer, 

 Galvani, who, somewhere about 1790, discovered that the limbs 

 of a dead frog might be excited to action by electricity applied 

 to the nerves. 



Afterwards, Yolta of Pavia, from whom the Yoltaic Pile is 

 named, took up Galvani's discoveries, and produced electricity 

 without friction, by the contact of differently conducting 

 substances. 



The right-hand figure represents the Voltaic Pile. It is 

 composed of a series of plates arranged in the following manner — 

 Zinc, Silver, and Cloth, the whole being moistened with diluted 

 acid. Copper will answer the purpose nearly as well as silver, 

 and is not so costly. A very simple mode of demonstrating 

 the presence of electricity is by taking a piece of zinc and a 

 silver coin, and placing one below and the other above the 

 tongue. If the two be then brought together, a very peculiar 

 taste is perceived, and a sudden flash of light seems to pass 

 across the eyes. 



The illustration represents on the right hand the Yoltaic 

 Pile as at present made, and on the left are the two hind-legs 

 of a frog, with the upper part of the nerves made bare for the 

 purpose of experimenting. The dotted lines show the extent 

 of the movements of the leg when the galvanic current is 

 passed through the nerves. 



Now we come to a plan whereby electricity can be accumu- 

 lated, or locked up, so to speak, and be discharged at once 

 with a definite shock instead of being poured away by degrees. 

 This can be done in many ways, the most common being that 

 which is known by the name of the Electric Jar. It is a glass 

 vessel coated within and without with tin-foil, and having a 

 metal rod passing through the cork in such a way that while 

 the lower end is in contact with the inner coating of tin-foil, 

 the other end is guarded by a ball. 



