cm. 
66 
PROF. J. JOLY ON THE GENESIS OF PLEOCHROIC HALOES. 
In later stages we find development progressing just as in the uranium halo. We 
may have the third ring as well as the fourth ring. The derivation of these haloes 
from the emanation can, of course, only be inferred when the inner structure is 
visible. 
Table -V.—Emanation Haloes. 
n. 
T. 
1 
0-0139 
0-0172 
2 
0-0143 
0-0176 
3 
0-0146 
0-0176 
4 
0-0148 
0-0176 
5 
0-0143 
0-0172 
6 
0-0141 
0-0172 
7 
0-0141 
0-0172 
8 
0-0137 
0-0172 
9 
0-0141 
0-0172 
10 
0-0141 
0-0174 
11 
0-0141 
0-0174 
0-0142 
0-0173 
Mean radius of nucleus O'0009 mm. 
These results for the inner and outer radius of the emanation embryonic ring are, I 
think, very reliable. The measurements are comparatively easy. The question as 
to the allowance for the nucleus, however, presents some difficulty. As will presently 
be seen, there is evidence that these haloes originate by the occlusion of emanation 
on nuclei placed in veins or conduits in the mica. If the occlusion is a surface 
phenomenon, the entire nuclear radius should be deducted in order to ascertain the 
range. This has been done in the figures given in the Table. If the emanation was 
absorbed throughout the nucleus, then the deduc¬ 
tion should more correctly be half the radius. To 
make this correction, we may add half the mean 
nuclear radius to the mean values of r 1 and r, as 
given at foot of the Table. 
Fig’. 4 shows the curve of ionisation in air of an 
c5 
emanation halo supposed to be formed in air. It 
is derived from emanation and its derivatives in 
exactly the same manner as fig. 1, and, as in the 
case of fig. 1, the added ordinates have been 
divided by 4 for convenience in plotting. I have 
6 
5 
T 
3 
o 
A 
f 
1 \— 
t 
i 
t 
W 
X 
1 
''' 
V 
V 
*1 
b 
• 
\ 
\ 
y' 
\ 
\ 
V 
V 
1 
\ 
\ 
i 2 2 
A 
d 5 6 7 
Fig. 4. 
cm. 
shown just above the curve the location of the 
originating ring-halo. The closest agreement is obtained on the supposition that 
the deduction for the nucleus is one-half the radius of the latter. The principles 
