1896.] Electricity thro' Dielectrics traversed by Rontgen Rays. 139 



These results are plotted in the curve shown in Fig. 10. The 

 ordinates are again proportional to the square roots of the time 

 and the abscissa? to the distances of the centre of the disc from A. 

 The results are represented by a straight line which cuts the 

 horizontal axis at a point corresponding to a point in the tube 

 about 7 centimetres behind A, i.e. the rate of leak varies 

 inversely as the square of the distance from a point behind the 

 plate. 



Absorption of the Rontgen rays by sheets of tinfoil. A number 

 of experiments were made on the effect produced by inserting 

 between the vacuum tube and the gas exposed to the Rontgen 

 rays sheets of tinfoil in gradually increasing numbers. The result 

 of these experiments would seem to indicate that the rays are not 

 all of one kind, for it was found that the effect produced by the 

 insertion of a given number of leaves of tinfoil was greater when 

 the number of leaves already placed between the vacuum tube 

 and the gas was small than when it was large. This effect would 

 occur if some of the rays were readily absorbed by the tinfoil, 

 while others passed through with greater facility. Thus when the 

 rays had already passed through a number of layers of tinfoil 

 most of the more absorbable rays would be already absorbed, and 

 any more leaves of tinfoil would only have the less absorbable ones 

 to deal with. The effect is very marked with some bulbs, though 

 it is hardly noticeable in others. 



We shall first give a specimen of the results obtained with a 

 bulb showing this effect. 



Thus to take a few examples, the effect of increasing the 

 number of leaves from 2 to 10 is to diminish the rate of leak 



