86 
Transactions of the Royal Society of South Africa. 
experimentally by Whiddiiigton (' Proc. Eoy. Soc./ a, Ixxxvi, p. 375, 1912), 
are in the ratio of 4*76~5. 
The maximum velocity of a corpuscle of the slower group, that associated 
with " L " characteristic radiation from gold, was calculated from the 
relationship — 
Jmv2 = ak(^»^)k — Aui^^L + hv^ + etc.) 
Energy of ex- Quantum of incident Potential energy of particle within 
pulsion. energy. the atom. 
which gives a value 65 x 10^ cm. /sec, and therefore that of the faster 
corpuscle associated with "M" characteristic radiation from gold =. 96 x 10^ 
cm. /sec. 
Whiddington's value for this is 108 x 10^ cm. /sec. (maximum velocity 
of a corpuscle ejected by silver X rays), whilst the mean of the values of the 
velocity of a parent cathode particle producing silver X rays (series K) 
calculated from the results of Rutherford, Barnes, and Richardson (' Phil. 
Mag.' [6], XXX, p. 352, 1915), from Duane and Hunt (' Phys. Rev.,' vi, 
p. 169, 1915), and from ^mv"^ = Af;(^v)K is 96-5 x 10^ cm. /sec. In writing 
down the above formula it is assumed that only one quantum of incident 
energy is absorbed, and that the nearer a particle be to the nucleus of an 
atom the greater will be the energy required to l>ring it to the surface before 
expulsion. 
University of Cape Town. 
Read August 21st, 1918. 
