\ 
Velocities of Two Groups of Bays and their Absorption Coefficients. 81 
Part II. 
It has been shown in Part I that the absorption coefficients of corpuscular 
rays in various gases, found by a method similar to that adopted by Beatty 
in 1910 for air and hydrogen, are probably too high. The reason becomes 
apparent from a critical examination of the cathode ionisation curves. It 
was stated that they proximated to the form = No (1 — e-^-''), which 
gives a logarithmic fall in the ionisation-density curve from the gold leaf 
backing the ionisation chamber, forwards. In this way a logarithmic 
a])sorption coefficient was found. 
Plotting the logarithms of No — Nj. against x (or p) should result in a 
Fig. 6. 
straight line. The cathode ionisation curves for the four gases were care- 
fully drawn, and the logarithmic curves deduced from them are shown in 
Fig. 5. The departure of these curves from linearity is at once apparent ; 
they are all concave upwards. On the air logarithmic curve, for example, a 
distinctly straight portion and a curved portion meet at B, and the curve 
shows no further tendency to " flatten out " beyond A. I therefore conclude 
that the slope of the line AB, which is perfectly straight, is a true measure 
of the absorption coefficient of the cathode particles and consequently a 
measure of their velocity. AB refers, however, to a faster group of particles, 
whilst CB refers to a slower group, as will be explained below. This latter 
group is completely absorbed in a distance ' j-p at a pressure P^, where 
this is the critical pressure for air for the faster group, P ' , the pressure at 
B and t the depth of the ionisation chamber. 
