6 ELEMENTS OF STATIC ELECTRICITY. 



stance of such low resistance that it can be used practi- 

 cally for the transfer of electricity; and a N OX-CON- 

 DUCTOR is any substance of such high resistance that it 

 can be used practically to prevent such transfer. 



LIST OF CONDUCTORS AND NON-CONDUCTORS. The 

 principal conductors are the metals, silver and copper 

 being the best. Among the partial conductors are the 

 different varieties of carbon, including coal, charcoal, 

 and graphite ; the acids, saline solutions, water, vegeta- 

 bles, and animals. 



The principal non-conductors are caoutchouc, gutta- 

 percha, sulphur, and their compound, known as hard 

 rubber, vulcanite, or ebonite ; dry air, paraffin, shellac, 

 amber, resin, glass when free from metallic substances, 

 mica, silk, fur, wool, hair, feathers, bisulphide of carbon, 

 petroleum, and oil of turpentine. 



Among the partial non-conductors are porcelain, 

 baked wood, paper, and leather. 



INSULATOR DEFINED. When a non-conductor is 

 used in connection with a conductor to confine elec- 

 tricity within certain limits, it is called an insulator; 

 and the conductor on which the electricity is confined, 

 or to be confined, is said to be insulated ; as a metal 

 placed on a glass or ebonite support, a copper wire 

 wrapped with silk or wool. 



QUANTITY AND INTENSITY. Electric quantity and 

 intensity are similar to the quantity and intensity found 

 in other more familiar forms of energy. The intensity 

 of any form of energy, other things being equal, is in- 

 versely proportional to the mass of the body in which it 

 is developed. A few strokes of a hammer on a small 

 piece of iron placed on an anvil will raise its temper- 

 ature to a burning heat; while the same number of 



