﻿42 Mr. Gr. H. Henderson on the 



Consequently^ the value o£ T is 



r-^ r -2[(w + 3)(\ + 2 A t)+\] (a n+2 -r- +2 )a n /in+4,)(n^ 2) 

 and 



2 



P ~ r ~\ + 2fi 



1ST 



V 



>-l 







XanK +2 (n + 4\4-2/i + 3yL6)/2(\ + ^)-r"+ 2 }/(v^ + 2)(// + 4). 



Higher approximations to the value of rj can be obtained 

 by the method adopted in the case of uniform density. 



IV. The Straggling of a Particles by Matter. By Gr. H. 

 Henderson, M.A., 1851 Exhibition Scholar of Dalhousie 

 University, Halifax , JW.S* 



§ 1. Introductory . 



WHEN a parallel beam of « rays passes through matter, 

 the particles gradually expend their energy in 

 passing through the atoms of the matter, until all trace of 

 the particles suddenly seems to vanish at the end of their 

 range. In passing through the atoms some o£ the a particles 

 lose more energy than others, so that at any point along 

 their path some of the particles will be moving more slowly 

 than others ; also their ranges will not all be the same. The 

 a particles may be said to be straggled out, and hence the 

 term straggling has been applied to "this phenomenon by 

 Darwin. 



The theory of: the passage of matter by a rays has been 

 developed on the basis of the nuclear structure of the atoms 

 of the matter, and from this theory the amount of straggling 

 to be expected has been deduced from probability, considera- 

 tions. On the other hand, the straggling can be determined 

 from experimental data in two ways. 



The first method makes use of ionization data. When the 

 ionization due to a parallel beam of a, rays is measured at 

 different points along the path of the rays, the well-known 

 ionization curve is obtained. This curve is shown as the 



* Communicated by Prof. Sir E. Rutherford, F.R.S. 



