EMISSION AND TRANSMISSION OF RONTGEN RAYS. 



135 



the least anomalous features in its transmission of any of the radiations. It would 

 seem, therefore, to be the most suitable material to use in determining the penetrating 

 power of a beam of rays. 



Atomic Weight of Radiator and Intensity of Rays. 



It was noticed on p. 130 that for aluminium screens thicker than about 2 mms. very 

 little change in the relative amounts of radiation from the different anticathodes is 

 caused by an alteration in the thickness of the screen. We are evidently here dealing 

 with beams of hard rays of similar composition. 



Under these conditions the intensity of the radiation, from a number of elements, 

 was measured, and the values are tabulated below. The liontgen rays used were 

 generated under a potential of about 22,000 volts, and a screen of aluminium about 

 2 mms. thick was employed; it cut down the initial radiation about 150 times. The 

 results are given below ; the radiation values are relative to that of platinum. The 

 value for silver is calculated from that of the amalgam Ag. Ilg, using a value for 

 mercury obtained from fig. G by interpolation. 



It will be seen that atomic weight and intensity of radiation increase together, the 

 latter a little more rapidly than the former. With higher potentials on the tube, the 

 metals of high atomic weight increase their radiation values relative to those of the 

 In fig. 6 the above intensities are plotted against atomic weight. 



lighter elements. 



