﻿Intelligence and Miscellaneous Articles. 579 



a quarter of the specific wave-length of the resonator ; the position 

 of the bridge is accurately noted. 



That done, I surround the part of the resonator forming; 

 the condenser with a watertight bag of parchment-paper which I 

 fill with distilled water, and then freeze this water ; the layer of 

 air is thus replaced by one of ice. Measuring the wave-length 

 afresh, it is found to be considerably greater than in the first 



experiment, having become —^ of what it was. 



The trough is then filled with water which is frozen, and then 

 the position of the bridge for disappearance of the spark is again 

 sought. Eor this purpose the ice at the distant end of the trough 

 is broken and progressively removed. I ascertained that this 

 position is exactly the same as in the first case, when the dielectric 

 was air. 



The experiment four times repeated, varying each time the 

 capacity of the condenser, always gave the same result. The pro- 

 position relative to the wave-length is therefore true for ice as 

 well as for other dielectrics. Hence, as shown in my previous 

 Note, Maxwell's relation that the dielectric power is also equal to 

 the square of the refractive index also holds for electromagnetic 

 waves in the case given. 



The preceding results, partly unforeseen, led me to determine 

 the dielectric constant of ice, using electromagnetic undulations. 

 The experiment cited above gave all the data necessary for this 

 determination. 



For if \ and \ are the wave-lengths corresponding to a given 

 resonator, working respectively in air and in a substance of dielec- 

 tric power K, we have 



As stated above, I found 



V_141 

 X 100' 

 whence K=2 in round numbers. 



The experiment repeated a dozen times always gave the same 

 result. I consider the relative error does not exceed -^, for the 

 plate of ice was almost entirely free from air-bubbles. According 

 to this, ice does not present exceptional dielectric properties. 



It remains to be explained how MM. Bouty and A. Perot 

 obtained values of a totally different order for the dielectric power 

 of ice. In the first place, in M. Bouty's method the charge and 

 discharge were enormously slower than in my experiments. Is it 

 not probable, then, that the physical magnitudes measured by 

 M. Bouty and myself were in themselves very different. In any 

 case we know at present too little about the dielectric properties 

 of bodies to be surprised at the divergences of numbers obtained 

 by two methods so dissimilar, however great they are. — Comptes 

 Rendus, October 8, 1894. 



