1901.; Electric Waves. 493 



WEEKLY EVENING MEETING, 



Friday, February 15, 1901. 



His Grace The Duke of Northumberland, E.G. D.C.L. F.R.S., 

 President, in the Chair. 



The Eight Rev. Monsignor Gerald Molloy, D.D. D.Sc. 



Electric Waves. 



Dr. Molloy said he had chosen tLe subject of electric waves, because 

 he thought it represented one of the most important scientific develop- 

 ments of the closing years of the nineteenth century. He proposed, 

 as far as might be within the limits of an hour, to give some general 

 conception of the nature of these waves, to sketch very briefly the 

 history of their discovery, and to show by a few simple experiments 

 how their existence might be demonstrated, and their properties 

 investigated. 



He began by calling attention to the essential characteristics of 

 wave motion, which he illustrated by a reference to waves of water, 

 waves of sound, waves of light and radiant heat. He then said that 

 the main purpose of his lecture was to bring home to them that 

 electrical energy was transmitted through space by a motion of this 

 kind ; and that the medium through which this motion was conveyed 

 was the ether, the same medium that served for the transmission of 

 light and radiant heat. 



Electric waves are most conveniently produced by a spark dis- 

 charge. It was shown long ago by Professor William Thomson, now 

 Lord Kelvin, that such a discharge, under certain conditions, was an 

 oscillating phenomenon ; that is, that the electric charge swings to and 

 fro, like a pendulum, several times before it comes to rest. Each such 

 oscillation would presumably involve some disturbance of the ether ; 

 these disturbances would be transmitted outwards and away in all 

 directions ; and following one another at regular intervals through 

 space, would constitute a series of electric waves. 



These ideas, which had been present, more or less vaguely, to 

 the minds of scientific men for some time, were put into the form of 

 a definite theory, supported by mathematical reasoning, by Professor 

 Clerk Maxwell, about the year 1864. According to this theory, 

 electrical energy is transmitted through space by vibrations or waves 

 of ether ; these vibrations travel with the same velocity as light ; 

 they are, in fact, vibrations of the same kind as light, differing only 

 in the matter of wave-length ; and if we could but increase the rate 

 of vibration, thereby diminishing the wave-length, they would be- 



