PROF. J. JOLY ON THE GENESIS OF PLEOCHEOIC HALOES. 
69 
existence of the shoulders or steps upon the ionisation curve, one of which apparently 
accounts for it, was unknown to me. This part of the curve had been put in with 
points spaced \ cm. apart and it was only in trying to account for the ring that the 
rugosities on the curve were discovered. 
The next stage of the thorium halo shows the first ring well darkened within and 
i 19 
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Fig. 6. 
cm. 
3 4 5 6789 
Fig. 7. cm. 
often obliterated, the second ring somewhat more definite and connected with the first 
ring by a certain amount of staining, and the fourth ring, due to ThCh, appearing 
faintly encircling all. The drawing, fig. 8, shows the appearance of the halo at 
this stage. 
The third stage which has come to my notice involves the obliteration of all the 
inner features within a deeply stained pupil. As in the case of all other halo-pupils 
the radial dimensions may be very various—in this case from (P023 to 0'028 ; and, 
l 2 
