the Absorption of X- Rays. 205 



in accordance with the circumstance that, as was previously 

 stated (p. 191), the number may probably be less than 8. 



Table XV. 

 K alCxi in r /" ra 7 s ' accor ding to Soddy and Russell. 

 Thorium D. Badium C. Mesothorium 2. Uranium X. 



Element. /* P ■ V I* K ,„ n i, B Pnlp 



-• *a/Cu- -• K a/Cu' -• K a/Cu* ~ "a/Our Obs. ^ aic - 



Cu 0-0334 100 0-0398 100 0-0423 100 0*0472 100 100 



Fe 0-0328 86"2 0-0399 87"9 0*0415 86-1 0-0472 87*8 871 83-7 



S 0-0369 558 0-0438 556 0-0465 555 0*0516 55*2 55-5 41*7 



Al 0-0324 41-3 00406 43-5 0-0421 42-4 0-0469 42-3 42-3 48J 



Paraffin-wax. 0-0361 0-0464 0-0580 0*0502 



Merely approximate calculations being here at issue, the 

 agreement of: the medium amounts of the observed and 

 calculated values of k lr , seems to be as good as can 



reasonably be demanded, more especially when considering 



that determinations of — for 7-rays are in a high degree 



dependent on the experimental arrangements *. 



In the case of the lighter elements absorption of 7-rays 

 will chiefly depend on the number of outer electrons, and this 



being the same or nearly the same the values of - for these 



elements must tend towards being the same. As for S, 

 however, the observed absorption coefficients seem to be 

 somewhat greater than what would have been expected 

 on account of the above-assumed number of outer electrons ; 

 but this question, I think, ought to remain undecided till a 

 wider range of observations on absorption of 7-rays is at 

 hand. 



The apparent anomaly that has been observed in respect 



to absorption in paraffin-wax, and that consists in - for this 



substance being equally great or even on some occasions 

 greater than for the heavy metals, may be explained in the 

 same way as was done for absorption of X-rays of very 

 short wave-length in case of Al and H 2 0. In paraffin-wax 

 there are, as we know, a great number of hydrogen atoms — 

 a fact that makes the number of outer electrons greater, 

 counted by mass unit, than in metals. 



* Comp. Kohlrausch, Jahrb. d. Had. v. Elektronik, xv. p. 93 (1918). 



