M. E. Edlund on the Nature of Electricity , 175 



back towards that point the ?ether which is in the vicinity of a. 

 As soon as the rarefaction about a has reached a certain limit, 

 the molecules enter a new state of equilibrium, which they pre- 

 serve as long as the increase of density at a continues. If now 

 the increase suddenly ceases, the molecules about a resume their 

 primitive equilibrium, and in this case travel, although in the 

 opposite direction, the same path as when the density was in- 

 creasing. 



A corresponding modification must be effected in the state of 

 equilibrium of the surrounding molecules if the sether at a be 

 rarefied instead of compressed ; but in this case the direction of 

 the motion of the molecules is the reverse of what it was in the 

 preceding : they approach a at the commencement of the rare- 

 faction, and recede therefrom when it ceases ; and the amount of 

 displacement is the same in the approach as in the recession. It 

 is moreover evident that the modification of the state of equili- 

 brium of a molecule, or the amount of its displacement, does not 

 depend exclusively on the modification of the repulsion of the 

 aether w^hich surrounds it to a certain distance, but depends also 

 on the facility with which it moves — or, in other terms, on the 

 resistance to conduction as well as on the action of the nearest 

 molecules. We have admitted, in the first part of this memoir, 

 that the action of one molecule upon another varies inversely as 

 the square of the distance. As v»re also indicated, this rule only 

 applies where the molecules are at a sufficient distance from each 

 other. If the molecules be in contact, or at a molecular distance 

 from one another, the lav/ of repulsion will perhaps be different 

 — a circumstance which in no way affects the present consi- 

 deration. 



It is obvious that the aether molecules about a will change 

 their position of equilibrium if, from any cause whatever, the 

 repulsion exerted upon them by the aether of a be modified with- 

 out becoming denser or rarer. Now the aether of a being set in 

 motion will produce a modification of this kind. If, then, that 

 aether be set in motion, the molecules of the surrounding aether 

 will be displaced, and will remain in their new positions as long 

 as the aether of a continues its motion without change. The 

 instant the motion ceases, the molecules return to their original 

 positions of equilibrium. 



Such, in our opinion, is the cause of galvanic induction. When 

 a galvanic current commences in the vicinity of a closed circuit, 

 the positions of equilibrium of the aether molecules are changed^ 

 not only in the closed circuit, but also in the insulating medium 

 encompassing it ; and the induction-current is simply the passage 

 of the molecules from the first position of equilibrium to the 

 second. The new state of equilibrium of the aether in the closed 



