ELECTRICITY AND GALVANISM. 58 



discovered the attractive power of amber ; and as the 

 Greek name for amber is electron, this science thence 

 obtained the name of Electricity. 



Although it was soon discovered that other substances 

 besides amber possess an attractive power, yet so little 

 attention was paid to the subject, that it was not until 

 the last century that electricity could be deemed a science. 



From its having been found that only certain sub- 

 stances could be excited- so as to produce electric effects, 

 these substances were called electrics ; and as those sub- 

 stances which cannot be excited have the property of 

 transmitting the electric excitement, they received the 

 name of conductors ; so that conductors are non-electrics, 

 and electrics are non-conductors.* 



The principal electrics are glass, resinous substances, 

 silk, hair, feathers, baked wood, and atmospheric air. 

 The principal conductors are the metals and fluids, living 

 animals and vegetables, most of the earths and stones. 



The usual mode of exciting electricity is by friction. 

 The process of heating will sometimes produce electricity, 

 but heating may be considered a species of friction. 



It may be naturally asked, what is electricity? In 

 reply, no satisfactory answer can be given. By some it 

 is considered a fluid sui generis ; by others a peculiar 

 affection of the surfaces of bodies. Electricity is identi- 

 fied with lightning, but it is only from the results pro- 

 duced by it that its existence is known. f 



As the effects of electricity appeared to differ by the 

 excitement of different substances of glass and sealing- 

 wax, for instance some philosophers imagined that 

 there were two different kinds of electricity, and these 

 they distinguished by the terms vitreous and resinous. 

 Others supposed there to be but one kind of electricity, 

 the difference in the effects being caused by the substance 

 excited possessing more or less than its natural share. 



* Although all bodies are considered to belong to one or other of 

 these classes, there are none that are either perfect conductors or per- 

 fect electrics ; also many conductors may be made to be electrics, and 

 many electrics to be conductors. 



t Sir Richard Phillips imagines electricity to be an affection of the 

 air, or medium intervening between the surfaces of bodies. 



