Ionization of Gases by the a, Particles of Radium. 333 



the fork current is insufficient, and recourse must be had to 

 independent driving by an electric motor or water-power 

 engine. If the driving power be in excess, the fork currents 

 are equally capable of holding the wheel back. The whole 

 behaviour is evident on observation of the fork through the 

 revolving apertures, and so long as the engagement lasts the 

 wheel can never gain nor lose a complete cycle relatively to 

 the fork. 



I have used the commutator thus driven to observe the 

 charges of a condenser in their passage through a galvano- 

 meter. The only inconvenience was the necessity of a 

 considerable separation between the galvanometer and the 

 rest of the apparatus to obviate magnetic disturbance. The 

 galvanometer deflexion was steady and apparently indepen- 

 dent of the force exercised at the springs of the commutator. 

 I believe that the arrangement might be used with advantage 

 in such work as determining the ratio of the electrical units. 



XXV. On the Ionization of Various Gases by the a. Particles 

 of Radium.— -No. 2. By W. H. Bragg, M.A., Elder 

 Professor of Mathematics and Physics in the University of 

 Adelaide *. / 



, [Plate IX.] 



Introduction. 



IN a paper w T ith a similar title (Proc. Roy. Soc. of South 

 Australia, vol. xxx. p. 1, and Phil. Mag. May 1906, 

 p. 617) I have given a preliminary account of an attempt to 

 determine the relative amounts of ionization produced in 

 various gases and vapours by the a particle of RaC. The 

 present paper contains an account of the further progress of 

 this work. 



In the first place, I have here discussed the validity and 

 the experimental details of the method used, and have brought 

 forward evidence in favour of the hypothesis that Be, the 

 ionization produced in consequence of the expenditure of a 

 small quantity of energy Se by the a. particle, is related to the 

 latter quantity by the equation 8t = kf(v)8e, where f(v) is a 

 function of the velocity of the particle only, and k a constant 

 for each gas. 



Secondly, I have given the result of the attempts to de- 

 termine for several gases the constant k, which may be called 

 the specific ionization of a gas for a radiation, air being taken 

 as the standard. 



* Communicated by the Physical Society of London : read February 22. 

 1907. Part of the paper was also read before the Royal Society of 

 South Australia, Oct. 2, 1906. 



