354 
PROF. C. G. BARKLA ON X-RAYS AND THE THEORY OF RADIATION. 
ionization in air • ‘i-i n* ■ , • n -i .-1 t •, i p ,-1 
7 —:- ; -:- rises with diminution ot wave-length, and with further 
ionization m copper 
diminution there is no return of the relative ionizations to the original value.* Thus 
the ionization in air increases beyond the spectral lines of air ; but there is no rise of 
the ionization in copper, as there is no spectral line characteristic-of copper within the 
range of wave-lengths used. The ionizations in aluminium and sulphur dioxide 
relative to that in copper may be obtained by division from the values more directly 
determined and plotted in fig. 6 ; the results are given in fig. 8 , from which we see 
Fig* 8. Showing approximate positions of the J spectral lines of N, Al, and S obtained from relative 
ionization curves. 
more clearly that these radiations characteristic of air, aluminium and sulphur, are 
progressively more penetrating. The J spectral lines for nitrogen, aluminium 
and sulphur obtained from these curves are shown at the foot of the figure. A 
similar increase of penetrating power with atomic weight of radiating substance had 
been found to hold among the radiations of series K and L. 
A point worthy of notice is that with primary radiation of much shorter wave¬ 
length than those of the characteristic radiations (J series) of the substances 
compared, the relative ionization is approximately the same as that obtained when 
The last two values in Table III., column IV., giving 
ionization coefficient in CoH 5 Br 
were 
b ionization coefficient in air (K, L, ...) 
corrected by the factors 1 • 32 and 1 • 39 respectively, because the observed ionization in air was partially 
due to J electrons. To obtain the ionization in air due to K, L, ... electrons alone, the observed total 
ionization had to be multiplied by (fig. 7), or the above fractions had to be multiplied by which 
CM AM 
had values 1 • 32 and 1 • 39 in the two cases, 
