182 ROYAL SOCIETY OF CANADA 



weak solution of eojipov sulphate was much more opaque than a similai* 

 solution of sulphuric acid, although the conductivity of the copper 

 sulphate was much less. 



In no case could we detect any evidence of any difiusion of the rays 

 as by passage through a turbid medium. The kathode rays investigated 

 ijv Lenard showed this ettect of ditfusion in a very marked manner in 

 atmospheric air. Some observers have stated that they found the same 

 effect with the X-rays. It is possible that an effect of this kind might be 

 found in the case of a fluorescent liquid. 



The rays in their passage thi-ough the liquid, certainly appeared to 

 undergo a kind of filtering process. In passing through the last milli- 

 metre of the solution, a much smaller proportion of the surviving rays 

 were absorbed than in the first millimetre. The weakening of the rays 

 was, however, much more raj)id than in simple jjroportion to the thick- 

 ness. Doubling the thickness of the layer in all cases appeared to 

 diminish the intensity bj^nuch more than half, but the ratio of reduction 

 a])peared to vary to some extent, according to the intensity of the source 

 as well as the thickness of the layers considered. 



Velocitij of the X-Rags. —We made some direct attempts to measure 

 the velocity of the X-rays, thinking that if they really consisted of 

 streams of electrified atoms, as some physicists imagine, the velocity 

 might turn out to be of measurable magnitude. As it happens, we have 

 only succeeded in establishing an inferior limit for the velocity, which is 

 practically a negative result, like the result of so many other experi- 

 ments on these rays, but it may be of value so far as it goes. 



Since the X-rays are not amenable to reflection or refraction, the 

 pi'oblem is not capable of so com])lete a solution as in the case of light. 

 The only prO])erty..in fact, which we were able to use for the purpose of 

 the experiment, was that of absor[)tion by a metallic screen. The method 

 adopted was somewhat analogous to that used by Fizeau in tl»e case of 

 light, but with certain modifications necessitated by the different proper- 

 ties of the rays. 



The rays were made to pass between the teeth of two rajiidly revol- 

 ving wheels fixed on a rigid axis at a distance of a metre ajjart. li' the 

 time occupied by the rays in traversing the distance between the wheels 

 were an appreciable fraction of the time of one revolution of the wheels, 

 certain aberration effects would evidently be introduced, the magnitude 

 of which would depend upon the velocity of the rays. We were 

 restricted to a distance of the order of a metre, both on account of the 

 necessary lightness and rigidity of the connecting shaft, and because 

 of the impos.sibility of obtaining a parallel beam of rays which could be 

 transmitted over greater distances without too great a loss of intensity. 

 The wheels were made nearly a metre in circumference, and we found it 

 possible to drive them at a speed of 25 revolutions per second without 



