Conductors in communication ill 



owing to the attraction and repulsion of the electric matter within the 

 body or close to its surface. And, secondly, because a body placed near 

 a positively electrified body receives electricity itself, whence it is supposed 

 to receive that electricity from the electrified body itself, and therefore 

 to be within its atmosphere. But, in all probability, the body in this case 

 receives its electricity from the contiguous air, and not immediately from 

 the electrified body, as will be further explained in its place. 



199] Let any number of bodies which conduct electricity with perfect 

 freedom be connected together by substances which also conduct elec- 

 tricity. It is plain that the electric fluid must be equally compressed * in 

 all these bodies, for if it was not, the electric fluid would move from those 

 bodies in which it was more compressed to those in which it was less 

 compressed till the compression became equal in all. But yet it is possible 

 that some of these bodies may be made to contain more than their natural 

 quantity of electricity, and others less. For instance, let some power be 

 applied to some of these bodies which shall cause the electric fluid within 

 their pores to expand and grow rarer f, those bodies will thereby be made 

 to contain less electric matter than they would otherwise do, but yet the 

 electric matter within them will be just as much compressed as it would 

 be if this power were not applied. 



On the other hand, if some power were applied which shall diminish 

 the elasticity of the electric fluid within them and thereby make it grow 

 more dense, those bodies will be made to contain more electricity, but 

 yet the compression will remain still the same. 



200] To make what is here said more intelligible, let us suppose a long 

 tube to be filled with air, and let part of this tube, and consequently the 

 air within, be heated, the air will thereby expand, and consequently that 

 part of the tube will contain less air than it did before, but yet the air in 

 that part will be just as much compressed as in the rest of the tube. 



In like manner, if you suppose the electric fluid to be not only confined 

 within the pores of bodies, but also to surround them in the form of an 

 atmosphere, let some power be applied to some of those bodies which 

 shall prevent this atmosphere from extending to so great a distance from 



* Note by Editor. [That is, must sustain an equal pressure. In modern scientific 

 language the words compression, extension, distortion, are used to express strain, 

 or change of form, while pressure, tension, torsion, are reserved to indicate the 

 stress or internal force which accompanies this change of form. Cavendish uses the 

 word compression to indicate stress. The idea is precisely that of potential.] 



f [No such power has been discovered. There is nothing among electrical 

 phenomena analogous to the expansion of air by heat. ED.] {Nowadays the free 

 electrons in a metal, or on a large scale in an incandescent star, are often treated 

 theoretically as constituting the molecules of a gaseous medium, responding to 

 change of temperature. It is interesting to compare the text with electron theories 

 of conductance and equilibrium. j 



