Changes produced hi Matter hy Eiedric Wares. 459 



Again, if the increase of resistance is due to a slight separation of 

 particles, suitable small increase of pressm^e ought to restore the 

 original conductivity, as also the sensitiveness. It is, however, found 

 that a considerable pressure is required to restore the original current, 

 as if the outer layers of the particles were rendered partially non-con- 

 ducting by radiation, and had to be broken through before the original 

 current could be re-established. It is also found that though the 

 sensitiveness is restored by this expedient of increasing the pressure, 

 yet the restoration is only partial, and that after a repetition of this 

 process the receiver loses its sensitiveness almost completely. 



I have attempted to find out an explanation of this obscure " fatigue " 

 ielfect. This subject will best be treated in connection with the 

 anomalous behaviour of silver, which I find is also in a manner con- 

 nected with the fatigue effect. Sih'er, when subjected to radiation, 

 exhibits, as indicated in my last paper, sometimes an increase, and at 

 other times a decrease, of resistance. The difficulty in this case cannot 

 be explained on the supposition of variations of radiation intensity, as 

 the anomaly persists even when che intensity of radiation is maintained 

 uniform by keeping the radiator at a fixed distance. 



In order to explain these actions, I assumed the following hypo- 

 theses, which, with the necessary deductions, are given below :— 



(1) That electric radiation produces molecular change or allotropic 

 modification in a substance. 



(2) That, starting from the original molecular condition A, the effect 

 of radiation is to convert it, to a more or less extent, into the allotropic 

 modification B (the latter condition will be designated as the " radia- 

 tion product "). It follows that this change from one state to the other 

 must be accompanied by a corresponding change in the physical pro- 

 perties of the substance. 



(3) As one of the properties of a substance is its electric conduc- 

 tivity, any allotropic changes produced by radiation should be capable 

 of being detected by a variation in the conductivity of the substance. 



(4) As a molecular strain is produced during transformation from 

 A to B, at a certain stage there may be a rebound towards the original 

 state A. Thus, after the molecular change from A to B condition has 

 reached a maximum value, the further action of radiation may be to 

 reconvert, to a more or less extent, B to A, this reversal of effect being- 

 indicated (see No. 3) by a corresponding electric reversal. 



(5) That the ultimate loss of sensitiveness, known as " fatigue," is 

 due to the presence of the radiation product, or strained B variety, 

 along wdth the A variety, the opposite effects produced by the two 

 varieties neutralising each other. 



The justification for the above hypotheses is to be sought for — 



(1) From analogy with other known radiation phenomena. 



(2) From experimental proof — 



