378 Mr. E. Eclser. An Extension of 



Hence (l-f-47rM) is the value of the specific inductive capacity 

 measured in the electro-static system. In the electro-magnetic 

 system (3) must be written 



where K is the dielectric constant of the ether. 



5. A few remarks may be made in connection with the assumptions 

 made in the course of the above argument. An objection might be 

 raised to the supposition that two oppositely charged atoms could 

 remain in equilibrium at a definite distance apart. To this it may be 

 replied that the form of the . argument does not necessitate the 

 assumption that electrical forces are the only forces acting ; and 

 even if these were the only forces, it would be possible to account for 

 the atomic separation by supposing both atoms to be revolving about 

 their common centre of gravity. 



If the atoms are considered to be small conducting spheres, and if 

 the volume actually occupied by the atoms is a large fraction of the 

 volume occupied by the dielectric, a correction on the lines of the 

 Mosotti-Clausius dielectric theory would become necessary. On the 

 other hand, if electrical conductivity is inseparably connected 

 with the motion of charged atoms, it would appear to be wrong to 

 consider the atoms themselves to be conductors. 



If finite motions of the atoms were necessary to explain the 

 properties of a dielectric, a treatment of the problem similar to that 

 used by Weber, in his molecular theory of magnetism would be 

 necessitated. It may, however, easily be shown that infinitesimal 

 atomic displacements will account for the observed phenomena. Take 

 the case of two plane and parallel charged condenser plates. Let P be 

 the electro- motive intensity at a point between the plates when 

 charged in vacuo. If now, the charge remaining the same, pure water 

 is introduced between the plates, the electro-motive intensity will 

 become 



4 irnqt) 



K 



if c = the average molecular displacement. Taking Cohn and Arons's 

 value for the specific inductive capacity of water, viz., 76, we havo 



Let P = 100 volts. Then, since nq will equal the total charge 

 carried by the oxygen in 1 gram of water, we shall have 



