ELEMENTARY LESSONS ON [CHAP. I. 



flow of electricity through them. There is indeed no 

 substance so good a conductor as to be devoid of resist- 

 ance. There is no substance of so high a resistance as 

 not to conduct a little. Even silver, which conducts best 

 of all known substances, resists the flow of electricity to 

 a small extent ; and, on the other hand, such a non-con- 

 ducting substance as glass, though its resistance is many 

 million times greater than any metal, does allow a very 

 small quantity of electricity to pass through it. In the 

 following list, the substances named are placed in order, 

 each conducting better than those lower down on the list. 



Silver 

 Copper . 

 Other metals 

 Charcoal . 

 Water . 

 The body . 

 Cotton 

 Dry wood 

 Marble . 

 Paper 

 Oils . 



Porcelain . 

 Wool 

 Silk . 

 Resin 



Gutta percha 

 Shellac . 

 Ebonite . 

 Paraffin . 

 Glass 

 Dry air 



A simple way of observing experimentally whether a 

 body is a conductor or not, is to take a charged gold- 

 leaf electroscope, and, holding the substance to be 

 examined in the hand, touch the knob of the electro- 

 scope with it. If the substance is a conductor the 

 electricity will flow away through it and through the 

 body to the earth, and the electroscope will be discharged. 

 Through good conductors the rapidity of the flow is so 



Good Conductors. 



I 



} Partial Conductors. 



Non- Conductors or 

 Insulators. 



