1889.] Electrolytes to very rapidly alternating Currents. 283 



the capacity of the condenser were exceedingly large, much greater 

 than that requisite for the same purpose in the preceding case, the 

 time of vibration would be independent of the capacities of the ends ; 

 and conversely, if we could prove that the time of vibration depends 

 upon the capacity, we should prove that v = 1. Now Hertz in his 

 experiments seems to have been able to bring two circuits into 

 resonance by altering the capacity of the ends, though these capa- 

 cities were exceedingly small compared with 1/10 of a microfarad. 

 This, therefore, is exceedingly strong testimony in favour of the 

 truth of Maxwell's theory, at any rate for conductors. 



[Note added February 15, 1889. We can find the ratio of i> T to i> 2 , 

 the values of v for a dielectric and conductor respectively, by con- 

 sidering the reflection of an electromagnetic disturbance at a metallic 

 surface. Using the notation of the beginning of the paper, let the 

 incident waves of the vector potential be expressed by 



F' = Ae i < ax+b y +cz \ 



G' = 

 H' = 

 the reflected waves by 



F/ = 



G/ = E'e l (- ax+b y +es \ 



H/ = 



Then assuming that 4:r/p/<7, & 3 + c 2 are large compared with 

 we find 



A' 



B' + B = 



Thus the electromotive force parallel to the surface of the reflector 

 does not vanish at the surface unless i> 3 = i/ ]t Hertz (' Wied. Ann.,' 

 34, 615) found that when the plane of tl^e secondary circuit was 

 parallel to the reflecting surface, the sparks vanished at the reflecting 

 surface, thus showing that i> 2 i> T is at any rate small. The method 

 founded on the law of decay of the vibrations is more delicate, as it 

 shows whether or not (v^v^na is small and na is a large quantity.] 



In the above work we have assumed that qa is small, but if qa be 



u 2 



