274 ELECTRICAL FORCES. SECT. XXVIII. 



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 pres- 

 sure 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 electricity, approaches it, that the mu- 

 tual repulsion of the particles of the electric fluid di- 

 minishes the pressure of the fluid on the air on the 

 adjacent sides of the two bodies, and increases it on 

 their remote ends ; consequently that equilibrium will 

 be destroyed, and the bodies, yielding to the action of 

 the preponderating force, will recede from or repel 

 each other. When, on the contrary, they are charged 

 with opposite electricities, it is alleged that the pressure 

 upon the air on the adjacent sides will be increased by 

 the mutual attraction of the particles of the electric 

 fluid, and that on the further sides diminished ; con- 

 sequently, that the force will urge the bodies toward 

 one another, the motion in both cases corresponding to 

 the forces producing it. An attempt has thus been 

 made to attribute electrical attractions and repulsions to 

 the mechanical pressure of the atmosphere. It is more 

 than doubtful, however, whether these phenomena can 

 be referijgpl to that cause ; but certain it is, that what- 

 ever theTiature of these forces may be, they are not 

 impeded in their action by the intervention of any sub- 

 stance whatever, provided it be not itself in an electric 

 state. 



A body charged with electricity, although perfectly 

 insulated, so that all escape of electricity is precluded, 

 tends to produce an electric state of the opposite kind 

 in all bodies in its vicinity. Positive electricity tends 

 to produce negative electricity in a body near to it, and 

 vice versa, the effect being greater as the distance di- 

 minishes. This power which electricity possesses, of 

 causing an opposite electrical state in its vicinity, is called 



