Changes produced in Matter hy Electric Waves. 457 



Is the effect of radiation due to'non-discriminative coherer action or to 

 the discriminative molecular action 1 That the effect is discriminative, 

 and therefore molecular, appears to be decisively proved by the experi- 

 ments described below. If further proofs are necessary, they are 

 afforded by the characteristic curves of variation of ciu*rent with the 

 E.M.F. given by the three types of substances, positive, negative, and 

 neutral ; by the continuity of radiation effect on matter ; and, lastly, 

 by certain remarkal)le results I obtained, which show that the effect of 

 ether waves on elementary substances depends on the chemical nature 

 of the substance ; in other words, the effect is found to be a periodic 

 function of the atomic weight of the substance. A detailed account of 

 the above will be given in a future paper. 



On the Change of Sign of liesponse in the Beceiver, due to a Variation of 

 Intensity of Radiation. 



After finding the increase of resistance exhibited by certain sub- 

 stances, I wished to see whether these showed any further difference 

 <is compared to substances which exhibit a diminution of resistance. 

 In my determination of the " Index of Refraction of Sulphur for the 

 Electric Ray,""^ I used the method of total reflection. I often noticed 

 that just before total reflection, when the intensity of the transmitted 

 beam became comparatively feeble, the receiver indicated an increase 

 instead of the usual diminution of resistance. Professor Lodge 

 mentions in one of his papers that an iron filing coherer exhibits an 

 increase of resistance when acted on by feeble radiation. Thus, if 

 positive substances like iron give a negative reaction, with the diminu- 

 tion of radiation intensity, negative substances may be expected to 

 give a positive reaction with feeble radiation. Very sensitive sub- 

 stances are, however, not so well adapted for an exhibition of this 

 reversed action, possibly because the range of sensibility is compara- 

 tively great. But it is not difficult to demonstrate this property in the 

 case of moderately sensitive substances. 



The following experiment with a moderately negative substance 

 (arsenic) and a moderately positive substance (osmium) will bring out 

 this interesting peculiarity in a clear manner. The intensity of incident 

 radiation may be varied in two ways — (1) by removing the radiator 

 further and further from the receiver, or (2) by using polarised radia- 

 tion, whose intensity may be varied by the rotation of an analyser. 

 In the experiment to be described, the first method was adopted. 



Experiments tvith Arsenic Receiver— K receiver was made of freshly- 

 powdered arsenic. The radiator used emitted radiation of strong 

 intensity. It was at first placed close to the receiver, and there was 

 produced a moderate increase of resistance. It was then removed 



* • Eoy. Soc. Proc.,' 1895, 



