926 



Dr. J. Chad wick and Mr. E. S. JBieler on the 



The interpretation of the experiments consists in deducing 

 from this relation the field of force around the a. particle, 

 and in finding what structure of the a. particle, or com- 

 bination of four H nuclei and two electrons, will give this 

 field of force. 



§ 3. Method of Experiment. 



In these collisions it is immaterial whether the hydrogen 

 is present in the form of hydrogen gas or in the combined 

 state as in paraffin wax. The use of paraffin wax as a 

 source of hydrogen has many advantages, and was preferred 

 in the present experiments. 



In fig. 1 let R be the source of a particles, AA' a thin 

 sheet of paraffin wax in the form of an annular ring, and 

 let a zinc-sulphide screen be placed at S on the axis of 

 the cone RAA', so that RA = AS. 



Fie-. 1. 



The solid angle subtended at R by an elementary annular 

 ring at P is 2ir sin 6/2 .d 6/2. If Q is the number of 

 5 particles emitted per second by the source, then the 

 number falling per second on this elementary ring is 

 Q/2 sin 0/2 d 0/2. 



Let the number of H particles projected within an 

 angle C by a single a particle in passing through 1 cm. 

 of hydrogen gas at N.T.P. be n = ¥(0). Then the number 

 projected between 6 and 6 + 86 is 8n = F'(6)S6, and the 

 number observed on a screen of unit area placed r cm. 



