CONDUCTORS AND NON-CONDUCTORS. 5 



To make this evident, let a short brass rod, of about 

 quarter inch diameter, terminating in a ball, be fitted to 

 an ebonite handle, as 

 represented by Fig. 3. 

 Let the brass be rubbed 



briskly on woolen, silk, Fi S- 3- The Insulated Metal Rod. 



or india rubber, holding the instrument by the handle, 

 and it will attract and repel the pith balls in the same 

 way as the other electrified substances already used. 

 Copper, iron, or any other metal may be substituted 

 for the brass with the same result. 



Kepeat the experiment, allowing the metal to touch 

 the hand, and the electric qualities disappear. This 

 shows that in the first experiment the electricity was 

 retained, because it could not pass through the ebonite 

 handle ; while, in the second, it passed off through the 

 hand. 



The results obtained by experiments of this kind led 

 to the abandonment of the doctrine of electrics and 

 non-electrics, and the classification of all bodies as con- 

 ductors or non-conductors. 



Experiment proves that all substances conduct elec- 

 tricity, and that they all offer a certain amount of 

 resistance to its passage. But it is found that the 

 relative proportions of conductivity and resistance vary 

 greatly in different substances. In some the conduct- 

 ivity is largely in excess, and they are called conductors ; 

 in others the resistance is- largely in excess, and they 

 are called non-conductors. Between these extremes 

 there are all degrees of variation ; so that in some sub- 

 stances the two properties are almost equally balanced. 

 Hence, since no exact rules can be given, we distinguish 

 the two classes by saying that a CONDUCTOR is any sub- 



