896 



Mr. A. L. McAulay on the Recoil of 



wax screen was 8*-4 cm. Curve H was made with two 

 types of radioactive source. One was a plate coated with 

 the active deposit from radium, giving a rays of range 

 about 6'S cm. incident on the screen. The points obtained 



Fii 



G and i\ e^erraicnfkl curva« (see zftt:en3) 



J_5£_d_JS. Curvfs derived rnm C? Knd rf 

 s^etf/tfe'y (.see setTien S) 



ZZ ZIl a& z$ 30 



— Ahsarbt'o-* (Js. etpw&.l&nT ans^ct &ir) 



in this way are plotted on the curve as crosses. The other 

 source was of thorium 0, the plate being covered with an 

 aluminium foil of stopping-power 1*5 mm. The a-rays had 

 a maximum range of from 6*9 to 6*7 cm. when they leached 

 the wax, according to the angle at which they passed 

 through the foil. The points so obtained are plotted on 

 the curve as circles. 



The number of a particles emitted from the source per 

 second was deduced from its 7-ray activity as measured 

 through G mm. of lead. No daia could be found for the 

 relation between the a- and 7-ray activities of thorium C, 

 so a preliminary investigation was made for its deter- 

 mination. This is described in a note at the end of the 

 paper. The fact that both sets of points on curve H fall 

 about the same line shows that the value obtained was 

 sufficiently accurate for the purpose. 



