84 M. E. Edlund on the Nature of Electricity. 



3. The action on the aether of B of all the surrounding me- 

 dium, with the exception of the aether contained in A. 



3. The action of the aether of A upon the aether which, if B 

 were removed, would occupy the space now occupied by B. 



4. The action of all the surrounding medium, except the space 

 occupied by A, on the aether which, if B were away, would 

 be found in the space last occupied by B. 



Evidently we have thus taken into account all the active causes. 

 The first two cases have reference to the efi'ect of all the sur- 

 rounding mass of aether upon the aether of B ; the last two, on 

 the contrary, express the same effect on the aether which would 

 be found in the place now occupied by B, if B were taken away. 

 Now, by taking the algebraic sum of the first two cases, and 

 subtracting from it the sum of the last two, we obtain, in accord- 

 ance with Archimedes^s principle, the expression of the motion 

 produced in B, This will be made evident by the applications 

 we shall immediately make. 



2. Electrostatic attractions and r^epulsions. — We assume that a 

 body which is said to be charged with positive electricity con- 

 tains more aether than when it is in the normal state, and that 

 the quantity of aether in an electro-negative body is less than 

 when its electric state is normal. The contrary might, perhaps, 

 be assumed; but several electrical phenomena seem to indicate 

 that the above-mentioned hypothesis is the true one. 



Naming a the quantity of aether contained in the bodies A 

 and B in their normal state, we will first consider the case in 

 which both are positive — A having the excess i, and B the ex- 

 cess b^. If the distance between the two bodies be r, and great 

 enough in proportion to the volumes of the bodies, the direct 

 repulsion between them can be expressed by 



{a-hb){a + b,) 

 r^ 



The action on B of all the surrounding medium, except the 

 space occupied by A, has evidently a resultant equal to the re- 

 pulsion which takes place between B and the aether of the space 

 occupied by A, and in a direction opposed to that repulsion. 

 This is clear ; for if A were removed, the resultant of the repul- 

 sion effected on B by all the surrounding medium would be 

 = ; consequently the action on B of all the surrounding me- 

 dium except the space occupied by A is the same as if B were 

 attracted by that space. We thus get, as the expression of the 

 action implied in this second case 



