X-Rays and Scattered X-Rayi 
295 
Though accurate experiments were not made on aluminium, 
it was found to behave in the same way. 
The penetrating power of the principal portion of the 
secondary radiation from Cr, Fe, Ni, Co, Cu, Zn has been 
found to be entirely different, being almost if not quite com- 
pletely independent of the penetrating power of the primary 
producing it. The origin of the radiation will be discussed 
elsewhere. The intensity from one of these we should expect 
not to depend on the direction of propagation of the primary. 
This is what was found for the radiation from copper. 
When, however, the behaviour of iron was compared with 
that of copper, it was invariably found that the ratio for 
iron was greater than that for copper. This is shown below. 
The three comparisons were made at different times. It 
appears to indicate a small amount of scattered radiation, 
though possibly not more than 2 per cent, of the total radia- 
tion from each atom. 
Radiator. 
1 
Time. 
1 
! 
Corrected 
deflexion 
of A v 
Corrected 
deflexion 
of A 2 . 
Eatio of 
deflexions 
A L :A 2 . 
Ratio of 
intensities of 
RA X and RA 2 . 
Cu 
Fe 
i 40 sees. 
! 25 „ 
22-3 
12 
29-8 
14-25 
75 : 100 
84 : 100 
1:1 
112 : 1 
Cu 
Fe 
40 „ 
50 „ 
27-5 
27-7 
42-45 
37-15 
65 : 100 
74:100 
1:1 
1-13:1 
Cu 
Fe 
! 75 „ 
\ 75 „ 
34-2 
267 
48-8 
34-55 
70:100 
77-2:100 
1:1 
1-10:1 
It seems quite possible from other considerations that a 
certain amount of scattered radiation does appear, as the 
atomic weight is getting near that for which a scattered 
radiation was found by much cruder methods. 
Again, Ag, Sn, Sb, I, &c. belong to quite another class of 
substances, for the radiation from these depends to an extra- 
ordinary extent upon the character of the primary. It has 
been shown that when primary rays of moderate penetrating 
power are used, this secondary is not a scattered radiation, 
though from tin its average penetrating power may be very 
like that of the primary producing it ; it is not polarized, 
and it does not give evidence of polarization in a primary 
where it exists. Though very different from the radiation 
from one of the elements in the Cr-Zn group, we should for 
these reasons expect the beam to show very little or no 
variation in intensity in the beams EAi and RA 2 . The results 
of comparisons with copper are given. 
