SOME SPECIAL MUTUAL CHANGES 71 



This explains why it does not gain the property when held in 

 the hand while being rubbed. 



48. Communication of the Property to Other Bodies. 

 When an electrified body is brought near to, or in contact 

 with, certain bodies, they may be shown to exhibit properties 

 similar to the electrified body itself. It is only those bodies, 

 however, which cannot be electrified unless held by a handle 

 of glass, ebonite, etc., which can have this property commu- 

 nicated. 



That kind of matter which suddenly loses when touched 

 by the hand, or, if held by the hand, cannot acquire, this 

 property, which may be termed ' electrification,' is called ' elec- 

 trically conducting matter,' or a ' conductor of electrification.' 



Good Conductors. 



Metals. 

 Carbon. 



Water containing salts in 

 solution. 



Sad Conductors, or Insulators. 



Gases. 



Oils. 



Ebonite. 



Paraffin. 



Resin. 



Gutta-percha. 



Caoutchouc. 



Porcelain. 



Glass. 



Sealing-wax. 



Silk. 



Sulphur. 



Wool. 



Shellac. 



49. Investigation of the Electric Field by a Small Elon- 

 gated Body, and also by Two Small Bodies. If a light elon- 

 gated body for example, a piece of pith suspended by a silk 

 thread at the end of a stick is brought into the space between 

 two bodies which have been rubbed and separated, it is always 

 caused to set itself lengthways between them. If displaced, 

 it returns to this position, sometimes with the ends reversed. 



If, however, instead of one elongated body, two small 

 bodies, such as two pith balls suspended side by side, are 



