EMISSION AND TRANSMISSION OF RONTGEN RAYS. 



129 



STAEKE* measured the relative numbers of secondary cathode particles emitted by 

 different metals under the bombardment of a beam of cathode rays. It is of interest 

 to compare his results with the corresponding ones of those just quoted. 



The order, which is not that of the atomic weights, is, with one exception, the 

 same in both cases. The absorption of the softest Rontgen rays by the aluminium 

 window probably explains part of the lack of quantitative agreement, especially with 

 the radiators of low atomic weight. We have, too, to remember that we are measuring, 

 by an ionisation method, the intensities of heterogeneous beams of rays, the components 

 of which have very different ionising powers. The general resemblance of the two 

 lists is, however, sufficiently noteworthy. 



To bring out any peculiarities in the radiation from any of the anticathodes the 

 ionisation values given by the electroscope are taken relative to that of one of the 

 metals platinum (which is kept constant and equal to 100 for all screens). These 

 relative values are plotted as ordinates against thickness of screen. Thus the graph 

 of the platinum radiation is a horizontal straight line, and if all the radiations were 

 similar in composition they would be represented by parallel straight lines. 



Figs. 3, 4, and 5 are thus obtained, and show how the Rontgen rays from lead, 

 platinum, silver, copper, nickel, iron, and aluminium, generated under a potential 

 difference of about 28,000 volts, are dealt with by screens of aluminium, copper, and 



* STARKE, < WIED. Ann.,' LXVL, p. 49 (1898); 'Ann. der Phys.,' III., p. 75 (1900). 

 VOL. CCIX. A. 8 



