898 Mr. A. L. McAulay on the Recoil of 



Table I. 



From 



curve 



G, 



1 



From curve 



H, 



a particles of rang 



e 8*4 cm. 



a particles 



of range 6-8 cm. 



N. 



cp. 



V. 





N. 



<p. 



V. 



1-39 x 10- 3 



15 



5-50 XlO 6 



■60X10- 5 



15 



4-79 xlO 6 



2-30 



20 



5 16 



113 





20 



4-50 



3-38 



25 



4-82 



1-81 





25 



4-20 



453 



30 



4-48 



2-61 





30 



390 



571 



35 



4-03 



3-48 





35 



3-51 



5. Deduction from the Absorption Curves of the results 

 given in the last section. 



The ordinates of curves G and H (fig. 2) multiplied 

 by '772 give the number of pairs of ions produced in the 

 ionization chamber divided by the number of u particles 

 involved in the production of the recoil radiation, and the 

 curves are obtained directly by experiment. 



Curves J and K are derived from G and H. J corre- 

 sponds to G, and K to H. The ordinate for abscissa R in the 

 case of the new curves represents the total ionization produced 

 by all atoms that pass R during the whole of the rest of 

 their course. J and K are obtained from G and H as 

 follows : — The absorption curves are marked off by vertical 

 lines drawn at intervals of 1*5 ' cm. (the depth of the 

 ionization chamber) starting from the maximum range. 

 Thus G, whose end is at 39 cm , is cut into sections by 

 lines at 37- 5, 36'0, 34*5, 33*0, etc. If the ordinates at 

 these points are a, b, c, d, etc., the new curve is constructed, 

 by drawing ordinates a, a + b, a-\-b-{-c, a + b-\-c + d, and 

 so on, at abscissae 37*5, 3(r0, 34*5, 33*0. As 1*5 cm. is 

 the depth of the ionization chamber, 'a' represents the 

 total ionization produced by those atoms which pass 37'5. 

 In the same way, '6' represents the total ionization pro- 

 duced by those which pass 36'0 but not 37*5, plus the 

 ionization produced by those which pass 37*5 in the part 

 of their course between 36*0 and 375. Thus a + b re- 

 presents the total ionization produced by the atoms which 

 pass 36"0. Similarly, it can easily be seen that a + b + c y 

 a + b + c+d, etc., represent the total ionization due to those 

 atoms that pass 34*5, 33"0 5 etc. 



A consideration of the geometry of the experimental 

 arrangement shows that the number of atoms entering 

 the ionization chamber which recoil at an angle 6 with the 



