1889.] on the Discharge of a Leyden Jar. 417 



imperfect elasticity, but partly also by the energy transferred to the 

 surrounding medium and consumed in the production of sound. It 

 is the formation and propagation of sound waves which largely damp 

 out the vibrations of any musical instrument. So it is also in 

 electricity. The oscillatory discharge of a Leyden jar disturbs the 

 medium surrounding it, carves it into waves which travel away from 

 it into space: travel with a velocity of 185,000 miles a second: 

 travel precisely with the velocity of light. [Tuning-fork.] 



The second cause, then, which damj)S out the oscillations in a 

 discharge circuit is radiation : electrical radiation if you like so to 

 distinguish it, but it differs in no respect from ordinary radiation (or 

 " radiant heat " as it has so often been called in this place) ; it differs 

 in no respect from Light except in the physiological fact that the 

 retinal mechanism, whatever it may be, responds only to waves of a 

 particular, and that a very small, size, while radiation in general may 

 have waves which range from 10,000 miles to a millionth of an inch 

 in length. 



The seeds of this great discovery of the nature of light were sown 

 in this place : it is all the outcome of Faraday's magneto-electric 

 and electrostatic induction : the development of them into a rich and 

 fall-blown theory was the greatest part of the life-work of Clerk- 

 Maxwell : the harvest of experimental verification is now being reaped 

 by a German. But by no ordinary German. Dr. Hertz, now Pro- 

 fessor in the Polytechnicum of Karlsruhe, is a young investigator of 

 the highest type. Trained in the school of Helmholtz, and endowed 

 with both mathematical knowledge and great experimental skill, he has 

 immortalised himself by a brilliant series of investigations which 

 have cut right into the ripe corn of scientific opinion in these islands, 

 and by the same strokes as have harvested the grain have opened up 

 wide and many branching avenues to other investigators. 



At one time I had thought of addressing you this evening on the 

 subject of these researches of Hertz, but the experiments are not yet 

 reproducible on a scale suited to a large audience, and I have been 

 so closely occupied with some not wholly dissimilar, but inde- 

 pendently conducted, researches of my own — researches led up to 

 through the unlikely avenue of lightning-conductors — that I have 

 had as yet no time to do more than verify some of them for my own 

 edification. 



In this work of repetition and verification Prof. Fitzgerald has, 

 as related in a recent number of Nature (February 21, p. 391), 

 probably gone further ; and if I may venture a suggestion to your 

 Honorary Secretary, I feel sure that a discourse on Hertz's researches 

 from Prof. Fitzgerald next year would be not only acceptable to you, 

 but would be highly conducive to the progress of science. 



I have wandered a little from my Leyden jar, and I must return 

 to it and its oscillations. Let me very briefly run over the history of 

 our knowledge of the oscillatory character of a Leyden jar discharge. 

 It was first clearly realised and distinctly stated by that excellent 



