Velocities of Two Groups of Mays and their Absorption Coefficients. 85 
diffusing through a gas the absorption coefficient varies inversely as the 
fourth power of their velocity,* whilst Whiddington came to a similar 
conclusion from experimental work.f I have shown that — 
^ 4 76 = 
and therefore the maximum velocity of the faster corpuscle = 96 x 10^ cm, /sec. 
This speed according to Whiddington = 10^ A, where A is the atomic weight 
of the metal supplying the X rays — silver in this case. He makes the speed 
therefore 108 x lO^cm./sec. This, however, is too high. He has shown that 
the maximum velocity of a particle is not greater than the minimum velocity 
of the parent cathode particle originally producing the X rays. By inter- 
polation from the results of Rutherford, Barnes, and Eichardson, the velocity 
of the parent cathode particle produced silver X rays of mean frequency 
5'855 X 10^^ is 98 x 10^ cm. /sec, by extrapolation from the results of Duane 
and Hunt 92 x 10*^ cm. /sec, and from the simple equation \mv'^= x^Qiv)-i^, 
93 X 108. 
Further work with thin films of other metals and with different radiators 
is in progress. 
Summary. 
Fart I. — The absorption coefficients in air, O^, COj and SO., of the 
secondary corpuscular rays from gold associated with the L, M, etc., charac- 
teristic radiations produced by the incidence of silver X rays upon it have 
been found by the "pressure variation" method. The results agree approxi- 
mately with Lenard's law and with Beatty's values (' Phil. Mag.,' [6] xx, 
p. 324, 1910) for air and H.i. It is shown, however, that the absorption 
coefficients obtained by calculation from the pressure at which the cathode 
ionisation falls to half its maximum value are probably too high for the 
fastest corpuscles produced. 
Part II. — To obtain as homogeneous a beam of particles as possible, a 
single very thin gold leaf was used as screen. 
On carefully analysing the logarithmic cathode ionisation curves for the 
four gases, it was found that over a fair range each consists of a straight 
portion giving a logarithmic absorption coefficient for a faster group of 
particles, merging into a steej^er curved portion rising to the axis x = 0, 
where x — distance from gold leaf, which was analysed with the help of the 
parent curve into a second straight portion giving a higher absorption 
coefficient than the first. The mean ratio of the two absorption coefficients 
is 4" 76. It is suggested that at least two distinct groups of particles are 
present whose velocities from Thomson's fourth power law, as verified 
* ' Cond. through Gases/ p. 381 (1906). 
t 'Proc. Roy. Soc./ a, Ixxxvi, p. 375 (1912). 
