OP ARTS AND SCIENCES. 25 



unoccupied space ? The only conductor between them is possibly 

 the moist air; but the same phenomenon takes place if the air be 

 dry, or even if it be entirely removed. The only remaining ex- 

 planation is that the pulsations are carried from one wire to the 

 other by means of the intervening ether which we know fills all 

 space. We shall see in a moment that the pulsations are trans- 

 mitted by means of a wave motion of the ether from the one wire 

 to the other. 



Meanwhile, let us look at the analogy of this phenomenon as it 

 takes place in a current of air. 



Suppose we have a pipe in which there is a steady current of air 

 flowing. Suppose ten feet away we place our ear. So long as the 

 current of air flows steadily on, no sound will be heard. If, how- 

 ever, the current in the pipe be broken up into rapid pulsations, 

 say 100 per second, by rapidly opening and closing its end, which 

 may be done by means of a reed such as is used in organs, the pipe 

 will radiate in all directions waves of musical sound of a pitch 

 due to 100 vibrations per second, and this sound will of course 

 be heard by the ear. In this case we have a current of air, by 

 rapid interruptions, converted into waves in the air, or sound. 



Analogy indicates that, in the former case, we had a current of 

 ether (or electricity), by rapid interruptions, converted into waves 

 in the ether (or electrical waves). But we must have stronger 

 proof than the indications of analogy, and it is readily forthcoming. 



If the interrupted current in the wire radiates ether waves, 

 these ether waves are really nothing more nor less than waves of 

 light. Unfortunately, the eye only detects waves of light that 

 are a small fraction of an inch in length, while the waves radiated 

 from the most rapidly interrupted electric current are many inches 

 in length. Nevertheless, the complete identity of waves radiated 

 from an interrupted electric current and from a source of light 

 has been confirmed by the study and identification of many of 

 their phenomena, first by Maxwell, and later by Hertz ; the 

 most striking proof being that waves radiated from an electric 

 wire are propagated through space with a velocity of 300,000,000 

 meters per second, which is the same as the velocitj r of light. 



So far as wave motions are concerned, therefore, those radiated 

 from an electric wire are just as much ether waves as those radiated 

 from the sun, or any other source of light. 



It remains now to show the identity of the electric current and 

 a current of ether. For this I invite your attention to some exper- 



