PROF. J. JOLY ON THE GENESIS OF PLEOCHROIC HALOES. 
55 
ranges of the eight rays of the uranium family, as cited in Rutherford’s 
‘ Radioactive Substances and their Transformations.’ The curve is put in according 
to a carefully made template. The added ordinates are reduced to one-fourth their 
full length. Fig. 2 shows the result of dividing the ordinates by the squares of the 
abscissae. Fig. 3 is, finally, the latter curve corrected for perspective in the case 
S' 18 
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Fig. 2. cm. 
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when the observed halo is a section symmetrical about the centre and 4 cm. thick— 
i.e., about one-third the diameter of the halo sphere.* 
* This last correction is a troublesome one. We assume the halo sphere divided into concentric shells, 
each, say, one half a centimetre thick, measured radially. To each of these shells we assign an intensity of 
ionisation, as defined by the ordinate of the curve of fig. 2 , taken at the centre of the half centimetre. 
Drawing these concentric shells on squared paper, and defining by cross lines the upper and lower 
boundary of the section, we can evaluate, at successive distances of one half centimetre from the centre, 
.the intensity of ionisation which would operate to darken the halo when this is observed by vertical rays 
proceeding from beneath. 
-O 
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Fig. 3. 
cm. 
