128] ELECTRICAL PHENOMENA. 245 



which allows electrical influences to pass through it, is called a 

 dielectric, as was proposed by Faraday*. 



EXPERIMENT III. Let the vessel be positively electrified by 

 induction as before, let a second vessel be suspended by silk 

 threads, and let a metallic wire, similarly suspended, be made to 

 touch both simultaneously. The second will be found to be 

 positively electrified, and the positive electrification of the first is 

 lessened. 



EXPERIMENT IV. If instead of a metal wire we had used a 

 rod of glass, sealing wax, or hard rubber, no such effect would have 

 been produced. Bodies may accordingly be divided into two 

 classes, 1, those which, like metals, allow a transference of electri- 

 fication from place to place. These are called conductors. The 

 second body above is said to be electrified by conduction : 2, those 

 which do not allow such transfer. These are called non-conductors 

 or insulators. The dividing line cannot be drawn with perfect 

 sharpness, since no bodies have been found to be absolutely non- 

 conducting. All insulators are dielectrics, but not all dielectrics 

 are necessarily insulators. 



EXPERIMENT V. In Experiment II it was shown that the 

 external electrification of the vessel due to the introduction of the 

 electrified glass was independent of the position of the latter in 

 the vessel. If we now introduce the piece of glass together with 

 the piece of resin with which it was rubbed, without touching the 

 vessel, the electrification of the latter disappears. We therefore 

 conclude that the electrification of the glass and resin, which are 

 able to counteract each other's effects, are equal in amount. By 

 putting in a number of bodies, and examining the external field, 

 we may show that the induced electrification is proportional to 

 their algebraic sum. We thus have an experimental method of 

 adding the effects of several electrifications without altering the 

 electrifications. 



EXPERIMENT VI. Let there be two insulated metallic vessels, 

 A and B, and let the glass be introduced into A and the resin 

 into B, and let them be connected by a wire. All electrification 

 disappears, as was to be expected. Now let the wire be removed, 

 and then let the glass and resin be taken out. It will be found 



* Exp. Res., 1168. 



