206 On the Absorption of X-Rays. 



Taking as granted that scattering merely depends on 

 outer electrons, we thus can easily account for tlie obser- 

 vations performed. It may therefore be superfluous to 

 assume that the electrons should behave otherwise for 

 different wave-lengths. On the contrary, we have every 

 reason for believing, a fact advocated by Glocker, the simple 

 law that was found valid for X-rays also to be in force 

 for y-rays. 



Summary. 



(1) By aid of the compensation method described by the 

 author for the purpose of determining the relative absorption 

 coefficients of X-radiation, a number of different elements 

 have been examined. 



(2) In the chemical compounds examined the additive 

 law has been found thoroughly valid. Perhaps with the 

 exception of carbon, the state of aggregation appears to 

 have had no influence on the quantity of absorption. In 

 examining chemical compounds of which the same element 

 but in different valences is a constituent part, I have not 

 been able to ascertain any difference as to the quantity 

 of absorption of the element at issue. 



(3) The relation between the atomic absorption coefficients 

 for most elements, starting from H and inclusive of Ag and 

 for Pb, and the same coefficient for Cu, have been deter- 

 mined at the medium wave-lengths \ = 0*38, 0*36, 0*34, and 

 0-30. 10" 8 cm. 



(4) On assuming that absorption for H is exclusively due 

 to scattering produced by the electron combined with the 

 atomic nucleus, scattering for other elements has been 

 found likely to be solely due to the electrons constituting 

 the outer layer of the respective atoms, i. e. to the " outer 

 electrons," and by aid of the relative atomic absorption 

 coefficient for H, the number of the outer electrons has been 

 estimated for the lighter elements. 



(5) The atomic absorption coefficient increases for different 

 elements by groups nearly proportionally to the atomic 

 number. If we accept that the atomic number gives the 

 number of electrons combined with the atomic nucleus, we 

 may by the increase of absorption with increasing atomic 

 number determine the distribution of electrons between the 

 outer and inner region. 



(6) From the determinations of - for Cu and H 2 of 



P 

 Barkla and White a formula of the mass scattering co- 

 efficient for different elements has been calculated. 



