20 NOMOS. 



all questioned, we will therefore assume that all 

 kinds of electricity are really identical, and proceed 

 once more to ask what is electricity? 



Before proceeding to put this question, however, 

 it may be well to arrive at some clear conception as 

 to the meaning of some terms in common use, such 

 as conduction and insulation, charge and discharge, 

 current and tension ; for this, we shall find, will ma- 

 terially facilitate our future inquiries. 



Electrically, bodies are divided into two classes 



conductors, and non-conductors or insulators; and 



this division may be illustrated by the 



The analogies J i-.ii- 



of the states working of the common electrical machine. 



called cow- __ ... n 



auction and The metallic parts are conductors; the 



insulation, -, 1,1 T 



charge mA glass parts and the surrounding air are 

 cwr?an<i non-conductors. On turning the handle, 

 tension. electricity is developed in the plate or 

 cylinder by friction against the rubber, and this 

 electricity is communicated to, or " induced " in, the 

 conductor. There the electricity is conducted into 

 every part of the "conductor," for, as its name 

 implies, this part of the machine belongs to the class 

 of conductors. The "conductor," however, rests 

 upon a glass foot, and is surrounded by air ; and as 

 glass and air belong to the class of non-conductors, 

 the electricity is not conducted beyond the limits of 

 the " conductor." The " conductor " is insulated by 

 the non-conducting glass and air ; and because it is 

 insulated, the electricity cannot be conducted away ; 

 and, not being conducted away, the conductor is said 

 to be charged. If there was no insulation, the elec- 



