634 HENEY A. KOWLAND 



This to me is one of the most wonderful facts in electrical science, and 

 lies at the foundation of our science. It cannot be ignored in any fur- 

 ther progress we may make in electrical theory, but points out a radical 

 difference between electrostatic and electro-magnetic action. 



I have said there is no action of a magnet in displacing an electric 

 current, and have thus stated the broad general fact, and which is per- 

 fectly true in some metals. But in others there is a small action which 

 changes in direction with the material. The elements of the electric 

 current within the material are rotated around the lines of magnetic 

 force, sometimes in one direction and sometimes in the other, according 

 to the material. But the action is, in all cases, very weak. When ap- 

 plied to the electro-magnetic theory of light, this action leads to the 

 magnetic rotation of the plane of polarization of light. As to the ex- 

 planation of both these actions, Thomson has remarked in the case of 

 light, from dynamical considerations, the rotation can only come from a 

 true rotation of something in the magnetic field, and leads us to think of 

 all magnetic action as of the nature of vortex motion in a fluid. But 

 here our theory ends for the present. We have obtained a clew, but it 

 is not yet worked up. 



I have now taken a rapid glance at some of the modern advances of 

 electrical science, and we have not yet had to give up the old idea that 

 electricity is liquid. To the profound thinker this idea is very vague, 

 and there are some facts at variance with it, but it is still useful. We 

 often hear persons say that this old idea is gone, and that electricity is 

 " force," whatever they may mean by that. But let us see. The work 

 or energy of an electric current between any two points is the quantity 

 of electricity passed multiplied by the potential; this work goes to 

 heating the wire. Let a curient of water be passing in a pipe, and the 

 quantity of water multiplied by the difference of pressure between two 

 points gives us the work which has been done in the intervening space, 

 and which has produced heat. The analogy is complete. No electricity 

 has been destroyed in the one case, or water in the other, but the work 

 has come from the fall of potential in the one case, and the fall of 

 pressure in the other; the resultant is the same in both heat. Again, 

 we can obtain work from the mutual attraction and repulsion of elec- 

 trified bodies, and the work in this case always comes from the change 

 of potential between the bodies while the electric charges remain undis- 

 turbed in quantity. Electricity, then, is not energy, but is more of the 

 nature of matter. 



So far for electricity in the state of rest or steady flow. But when it 



