Rontgen Radiation from Substances of Low Atomic Weight. 139 



used ordinary primary beams, we expected to find that the 

 scattered radiation from carbon excited by a homogeneous 

 beam would be itself homogeneous and of the same cha- 

 racter as the primary, i. e. if we placed a thin sheet of 

 absorbing material in the path of the scattered beam the 

 percentage diminution in intensity would be equal to that 

 occurring if the same sheet were used to cut down the 

 primary beam. 



A reference to fig. 1, a diagrammatic representation of the 



Fte. 1. 



TcRTIARY ft/IO/ATOfi 



TERTIARY fiBSORBCRS. 



?w Volts. 



Seconmrv 



Ab&ORBERS. 



i W/MXW ZcnxScm. 



\ COVERED tr/TH 

 '"* T/SSUE RARER 

 \/)ND /li.roiL. 



Secondary 

 tuctroscore 



To Compensator charged to -efo Volts 



To Electrometer 



apparatus used for making measurements, shows that the 



tertiary rays from the carbon enter the ionization chamber, 



on the whole, by more oblique paths than is the case with 



the secondary radiation, which consists of a nearly parallel 



beam. A correction must be made for this obliquity, since 



the length of path of the oblique rays in their passage 



through the absorbing substance is greater than that of rays 

 © © © «. 



which traverse the absorber perpendicularly, and thus a 

 correspondingly greater relative absorption takes place. On 

 the other hand, some of the oblique rays have only a small 

 range within the ionization chamber, and thus do not con- 

 tribute much to the ionization. 



(An electroscope of the usual Wilson type received a small 

 pencil of rays from the primary beam. In making measure- 

 ments of the absorption of the tertiary beam, readings of the 

 primary electroscope and the tertiary electrometer were 

 taken before and after the introduction of the absorber into 



