M. E. Edlund on the Nature of Electricity, 87 



the external molecules of aether must therefore tend to repel the 

 sether within the body from the surface to the central parts. 

 Let us now suppose a body presenting a deficit of aether^ having 

 less than the quantity required for equilibrium ; the resultant 

 of the repulsion of the external molecules will necessarily have 

 the preponderance, and the aether molecules of the body will be 

 driven from the surface to the interior. As, then, the body con- 

 tains a less quantity of aether now than when it is in the neutral 

 state, the result must be a deficit at the surface. 



The condensation of the aether when a Leyden jar or a Frank- 

 lin^s tray is charged may be explained in an analogous manner : 

 the current of the electric discharge is simply the passage of the 

 aether out of one body into another"^. 



* As we know, FrankUn attempted to explain the electric phenomena 

 known in his time by admitting only one electric fluid. He could not, 

 however, account for the repulsion between two electronegative bodies 

 without attributing to ponderable matter properties which it does not pos- 

 sess. For this cause the opinion of Franklin and the " unitarians " on the 

 nature of electricity had to give place to that of the dualists, who established 

 the hypothesis of the two fluids, admitted to this day. Some attempts 

 have been made recently with a view to explain electric phenomena as pro- 

 duced by the aether or a single fluid. Without entering into a detailed 

 account of these more or less happy endeavours, we think it necessary to 

 observe that, relatively to the properties or the motions of the aether, they 

 are founded on premises the justness of which may with reason be ques- 

 tioned, — and, further, that the theories in which they have ended are far from 

 having the seal of simplicity, which assuredly they would have had, if they 

 had been the real interpretation of the facts. The theory of light presup- 

 poses that the aether in a ponderable body varies in density with the body, 

 and that its density remains the same as long as the body undergoes no 

 modification. It must, consequently, be admitted that different sorts of 

 ponderable matter exert different degrees of attractive force upon the 

 aether molecules. A material body condenses within itself aether from the 

 surrounding mass of aether until the resultant of the effects produced upon 

 an external aether molecule by the proper molecules of the body and by the 

 excess of aether included within the body becomes =0. With a body thus 

 saturated the repulsion between its excess and an external aether molecule 

 is equal to the attraction between the same molecule and the material mo- 

 lecules of the body. If, then, we are forced to admit, for the explanation 

 of luminous phenomena, that, in virtue of the attraction exerted upon it by 

 matter, the aether presents degrees of density varying with the bodies, it 

 does not follow that on this account the bodies must exhibit certain elec- 

 tric properties. If, on the contrary, we increase or diminish in one way or 

 other the quantity of aether which the body contains in its normal state, 

 electrical phenomena begin to show^ themselves. It nevertheless is not an 

 immediate consequence of this, that electrified bodies must give evidence 

 of other optical properties than in their natural state. The velocity of pro- 

 pagation of light, and consequently also the wave-lengths, do not depend 

 exclusively on the density of the aether, but on the ratio between its elas- 

 ticity and its density. If, therefore, the elasticity of the aether be increased 

 or diminished proportionally with its density, no modification can happen 

 relative to the velocity of propagation of light, refi action, &c. The fact 



