312 ELECTETCS. [SECT, xxvur. 



become electric. When separated, the white riband is found 

 to have acquired positive electricity, and the black has lost 

 it, or become negative ; but, if the whole length of the black 

 riband be drawn across the breadth of the white, the black 

 will be positively, and the white negatively, electric when 

 separate. Electricity may be transferred from one body to 

 another in the same manner as heat is communicated ; and, 

 like it too, the body loses by the transmission. Although no 

 substance is altogether impervious to the electric fluid, nor 

 is there any that does not oppose some resistance to its pas- 

 sage, yet it moves with much more facility through a certain 

 class of substances called conductors, such as metals, water, 

 the human body, &c., than through atmospheric air, glass, 

 silk, <fec., which are therefore called non-conductors. The 

 conducting power is affected both by temperature and 

 moisture. 



Bodies surrounded with non-conductors are said to be in- 

 sulated, because, when charged, the electricity cannot escape. 

 When that is not the case, the electricity is conveyed to the 

 earth, which is formed of conducting matter; consequently, 

 it is impossible to accumulate electricity in a conducting 

 substance that is not insulated. There are a great many 

 substances, called non-electrics, in which electricity is not 

 sensibly developed by friction unless they be insulated, pro- 

 bably because it is carried off by their conducting power as 

 soon as elicited. Metals, for example, which are said to be 

 non-electrics, can be excited; but, being conductors, they 

 cannot retain this state if in communication with the earth. 

 It is probable that no bodies exist which are either perfect 

 non-electrics or perfect non-conductors. But it is evident 

 that electrics must be non-conductors to a certain degree, 

 otherwise they could not retain their electric state. 



It has been supposed that an insulated body remains at 

 rest, because the tension of the electricity, or its pressure on 

 the air which restrains it, is equal on all sides ; but, when a 

 body in a similar state, and charged with the same kind of 



