PROF. J. JOLY ON THE GENESIS OF PEEOCHROIC HALOES. 
(II 
Nos. 4, 5, and 6 are readings on three haloes which Prof. H. H. Dixon, F.Pv.S., was 
so good as to make. These measurements were obtained without any possibility of 
preconceived ideas influencing the judgment one way or the other. My own 
independent readings on these same haloes same in the mean to exactly the same 
figure arrived at by Prof. Dixon. Nos. 12 and 13 are measurements made by 
Mr. L. B. Smyth, Lecturer in Palaeontology in the School of Geology. These 
readings were obtained under the same conditions as obtained in the case of 
Prof. Dixon’s measurements. 
Table I.—Uranium Haloes : the First Pine - . 
___ O 
n- 
r. 
Nuclear radius. 
l 
0-0112 
0-0134 
0•0004 
2 
o-oioi 
0-0149 
0-0004 
3 
0-0099 
0-0149 
0•0005 
4 
0-0098 
0-0142 
0-0006 
5 
0-0109 
0-0153 
0-0006 
G 
0-0106 
0-0150 
0-0006 
7 
o-oioo 
0-0139 
0-0006 
8 
0-0101 
0-0142 
0-0006 
9 
0-0105 
0-0145 
0-0007 
10 
0-0106 
0-0142 
0-0006 
11 
0-0101 
0-0139 
0-0005 
12 
o-oioo 
0-0143 
0-0006 
13 
— 
0-0140 
— 
14 
00107 
0-0131 
0-0003 
15 
0-0113 
0-0137 
0•0008 
16 
o-ono 
0-0146 
o-ooio 
17 
0-0111 
0-0142 
0-0008 
18 
0-0113 
0-0142 
0-0008 
0-0105 
0-0142 
0-0006 
No feature whatever is found within these rings, save in the more advanced stages, 
when a uniform darkening of the region between the ring and the nucleus appears. 
Many of the haloes cited above show no trace of this darkening. These are in the 
earliest measurable stage. It is possible to glimpse haloes surrounding nuclei still 
more point-like but which are too indefinite to permit of satisfactory measurement. 
But there is no reason to ascribe to them dimensions different to those recorded above. 
Careful estimation, using a Leitz No. 5 objective, showed as the mean of seven 
observations that the width of the ring was to its outer radial dimension as 6'1 : 20‘7. 
This determination was made on a medium dark halo ; that is on one showing some 
darkening within the initiating ring. The same observation applied to a very faint 
ring gave the ratio as 5:19. There was less certainty here and it was found that 
the result might actually be 6 : 18. Using a lower power—a Leitz No. 3—another 
faint ring gave 37 : 27 as the ratio of the external to the internal diameter. This is 
nearly the same as the result 5:19 for ratio of width of ring to radius. Another 
k 2 
