MODERN VIEWS WITH RESPECT TO ELECTRIC CURRENTS 661 



wire, hung far away from other bodies and made of good conducting ma- 

 terial, is that of light, or 185,000 miles per second; but when it is 

 hung near any conducting matter, like the earth, or inclosed in a cable 

 and sunk into the sea, the velocity becomes much less. When hung in 

 space, away from other bodies, it forms, as it were, the core of a system 

 of waves in the ether, the amplitude of the disturbance becoming less 

 and less as we move away from the wire. But the most curious fact is 

 that the electric current penetrates only a short distance into the wire, 





Or 





- o 



DIAGRAM 1. 



being mostly confined to the surface, especially where the number of 

 oscillations per second is very great. 



The electrical waves at the surface of a conductor are thus, in some 

 respects, very similar to the waves on the surface of the water. The 

 greatest motion in the latter case is at the surface, while it diminishes 

 as we pass downward and soon becomes inappreciable. Furthermore, 

 the depth to which the disturbance penetrates into the water increases 

 with increase of the length of the wave, being confined to very near the 

 surface for very short waves. So the disturbance in the copper pene- 

 trates deeper as the waves and the time of oscillation are longer, and the 

 disturbance is more nearly confined to the surface as the waves become 

 shorter. I have recently made the complete calculations with respect 



