ELECTRICITY AND GALVANISM. 63 



using the glass handle, and touch the outside of the plate 

 with the finger, then if the outside plate be raised by 

 the handle, it will be found to be electrified, but with a 

 contrary electricity to the other, and will give a spark to 

 the knuckle, or any other conductor presented to it. By 

 replacing the plate, touching it with the finger, and rais- 

 ing it by the handle, as before, it will be again electrified, 

 and by this means a small coated phial may be charged. 

 The same phenomenon may be exhibited repeatedly 

 without any fresh excitement of the electric plate : when 

 the electric has been well excited, it has been known to 

 continue so for several weeks. Its action is said to be 

 caused through the principle of an excited electric re- 

 pelling the electricity of another body, and giving it a 

 contrary electricity. Thus the outside plate being 

 touched by a conductor when in contact with the under 

 plate which is negatively electrified, it acquires an addi- 

 tional quantity from the conductor ; but if it were in 

 contact with a plate electrified positively, it would part 

 with its electricity to the conductor. 



The quantity of electricity in any body is measured by 

 an instrument called an Electrometer. This may consist 

 of a pair of pith-balls or pieces of gold-leaf suspended 

 by a thread, and by diverging or collapsing, it will indi- 

 cate the degree and quality of the excited body. 



It has been already stated that electricity is of the 

 same nature as lightning. Franklin was the first who 

 proved this ; for by means of a kite he drew the electric 

 fluid from the clouds, and found it by experiment to 

 produce the like results. In speaking cf lightning, it may 

 be observed that instruments called Paratonneres or Con- 

 ductors are used for the purpose of preventing the dread- 

 ful effects sometimes produced by this most destructive 

 element on ships and buildings. 



A conductor, when used to protect a building, generally 

 consists of a copper rod, pointed with iron at the top, 

 and so fixed that its extremity may be at some distance 

 above the highest point of the edifice, and connected 

 by a wire with the ground at some distance from its 

 foundation, \vhen, in the event of a storm of lightning, 

 the fluid will probably (if within its range) be attracted 



