| THE ETHER THEORIES OF ELECTRIFICATION |
By Professor FERNANDO SANFORD
Stanford University
IN a previous paper on "The Electric Fluid Theories" it was shown that neither the one fluid nor the two fluid theory gave any physical explanation of the cause of electric attraction or repulsion, though it was this explanation which was the principal purpose of the earlier emanation theory. It was also shown that a fundamental question which was left unsettled was how the electric fluid is held to a conductor while there is no attraction between it and the particles of matter.
The only theory proposed during this time which seems to suggest any explanation of this phenomenon was one proposed by Cavendish, who regarded the electric fluid in conductors as under an external pressure and as always flowing in the direction of least pressure. Cavendish did not discuss the question of the retention of a charge upon a conductor, for he regarded the electric fluid as being attracted by the particles of material bodies; but he seems to have had a very definite notion of an external pressure exerted upon the electric fluid in a charged body and of the reaction of the electric fluid to this pressure. Thus he says:
When the electric fluid within any body is more compressed than in its natural state, I call that body positively electrified. When it is less compressed, I call the body negatively electrified.
It is plain from what has been here said that if any number of conducting bodies be joined by conductors and one of these bodies be positively electrified, that all the others must be so too.
If two bodies, both perfectly insulated, so that no electricity can escape from them, be positively electrified and then brought near each other, as they are both overcharged they will each, by the action of the other upon it, be rendered less capable of containing electricity; therefore, as no electricity can escape from them, the fluid in them will be more compressed, just as air included within a bottle will become more compressed either by heating the air or by squeezing the bottle into less compass: but it is evident that the bodies will remain just as much overcharged as before.
It will be seen from the above quotations that Cavendish regarded the compressed electric fluid in one charged body as capable of transmitting in some way a pressure to the fluid in another body brought near it. This would seem to indicate that he supposed
