ELECTRICITY IN HdUILIBRItm. 



be considered as modifications of some other more general laws, 

 which are } rt wholly unknown to us. 



When the equilibrium of these forces is destroyed, the electric 

 fluid is put in motion ; those bodies, which allow the fluid a free 

 passage, are called perfect conductors ; but those which impede its 

 motion, more or less, are nonconductors, or imperfect conductors. 

 For eiample, while the electric fluid is received into the metallic 

 cylinder of an electrical machine, its accumulation may be pre. 

 Tented by the application of the hand to the cylinder which 

 receives Ft, and it will pass off through the person of the operator 

 to the ground ; hence the human body is called a conductor. But 

 when the metallic cylinder, or conductor, of the machine is sur- 

 rounded only by dry air, and supported by glass, the electric 

 fluid is retained, and its density increased, until it becomes capable 

 of procuring itself a passage, some inches in length, through the 

 air, which is a very imperfect conductor. If a person, connected 

 with the conductor, be placed on a stool with glass legs, the elec- 

 tricity will no longer pass through him to the earth, but may be 

 so accumulated, as to make its way to any neighbouring substance, 

 which is capable of receiving it, exhibiting a luminous appearance, 

 called a spark ; and a person or a substance, so placed as to be in 

 contact with nonconductors only, is said to be insulated. When 

 electricity is subtracted from the substance thus insulated, it is said 

 to be negatively electrified, but the sensible effects are nearly the 

 same, except that in some cases the form of the sparks is a little 

 different. 



Perfect conductors, when electrified, are in general either over- 

 charged or undercharged with electricity, in their most distant 

 parts, at the same time ; but nonconductors, although they have 

 an equal attraction for the electric fluid, are often differently 

 affected in different parts of their substance, even when those 

 parts are similarly situated in every respect, except that some of 

 them have had their electricity increased or diminished by a foreign 

 cause. This property of nonconductors may be illustrated by 

 means of a cake of resin, or a plate of glass, to which a local 

 electricity may be communicated in any part of its surface, by the 

 contact of an electrified body; and the parts thus electrified may 

 afterwards be distinguished from the rest, by the attraction which 

 they enert on any small particles of dust or powder projected near 

 them ; the manner in which the particles arrange tbemselvei on th 



