LIGHT AND ELECTRICITY, ACCORDING TO MAXWELL 



AND HERTZ.i 



By M. POINCARE.2 



It was at the moment when the experiments of Fresnel were lorcing 

 the scientific workl to admit that hght consists of the vibrations of a 

 highly attennated liuid filling interplanetary spaces that the researches 

 of Ampere were making known the laws of the mntual action of cur- 

 rents and were so enunciating the fundamental x)rinciples of electro- 

 dynamics. 



It needed but one step to the supposition that that same fluid, the 

 ether, which is the medium of luminous i)henomena, is at the same time 

 the vehicle of electrical action. In imagination Ampere made this 

 stride; but the illustrious i)hysicist could not foresee that the seducing 

 hypothesis with which he was toying, a mere dream for him, was ere 

 long to take a precise form and become one of the vital concerns of 

 exact science. 



A dream it remained for many years, till one day, after electrical 

 measurements had become extremely exact, some physicist, turning 

 over the numerical data, much as a resting pedestrian might idly turn 

 over a stone, brought to light an odd coincidence. It was that the 

 factor of transformation between the system of electro statical units 

 and the system of electro dynamical units was equal to the velocity 

 of light. Soon the observations directed to this strange coincidence 

 became so exact that no sane head could longer hold it a mere coinci- 

 dence. No longer could it be doubted that some occult affinity existed 

 between optical and electrical phenomena. Perhaps, however, we 

 might be wondering to this day what this affinity could be were it not 

 for the genius of Clerk Maxwell. 



' Trauslated from Annuaire du Bureau des Lougitudes, Paris, 1894. 



- M. Heuf i Poiucard, oue of the leadiug niathematicians of France, is the author 

 of a worlc entitled filectricite et Optique, in two vohuues, of which the first treats ot 

 the discoveries of Maxwell, the secoml of those of Hertz. 



SM 94 g 129 



