Absorption of Hard X-Rays m the Lightest Elements, 739 



same as the relation between the atomic numbers. Con- 

 cerning all elements as far as Cu inclusively, and within the 

 range of wave-lengths I have investigated, it is in all 

 probability true that the scattering effect is proportional to 

 the atomic number, and it is likely to be true also as regards 

 several elements immediately following Cu. On the contrary, 

 it is not true concerning the heaviest elements as it appears 

 from the determinations, made by the above mentioned 

 writers, as to the relation between the mass scattering 

 coefficients of Pb and Al. 



In the case of hard X-rays, it can be said with certainty 

 that the true absorption (/c a X 6 ) due to H m;iy be regarded as 

 infinitely small as compared with the scattering effect. Since, 

 in conformity to the current notion, there is only one electron 

 combined with the nucleus of an atom of hydrogen, then the 

 absorption observed in hydrogen must be equal to the scatter- 

 ing effect due to one electron. The mass scattering co- 

 efficient per electron can easily be calculated, when we know 



the mass absorption coefficient of Cu ( Cu) for the effective 



wave-lengths used in the experiment. If the values of tfcu/H 2 o 

 recorded in Table I. be corrected by deducting 29 ^ H /h 2 o 

 from them, we obtain the values 63*4, 47*0, 37 *7, 31*0, 25*8, 

 20*6 for the respective wave-lengths. By means of these 

 values we calculate from the values of a:h/h 2 o the scattering 

 coefficient per electron in relation to the true atomic absorp- 

 tion coefficient of Cu (q). In Table IV. we again find the 



values of q corresponding to values of ^Cu. 



P 



Table IV. 



I. II. III. IY. V. * VI. Mean. 



q 000107 0-00172 000233 0-00300 0-00372 0-00476 



^Cu ... 6-30 364 262 2-02 1-60 1-28 



q^Gu... [0-00674] 0-00626 000610 0-00606 0-00595 000610 0-00609 

 P 



The radiation of the greatest wave-length (I.) is probably 

 less homogeneous than the other radiations, which had to 

 pass through thicker filters. With the exception of the 



values of q ^ Cu £ or effective wave-length (J.), it appears 



from the table that q is inversely proportional to Cu, but 



