1895.] Mineralogy. 837 
cate apparatus described by him before the Royal Society, and also in 
the measurement of the optical angle (in sections prepared accurately 
normal to a besectrix by means of the same apparatus) in five different 
wave lengths of light. Here again the intermediate position of rubid- 
ium is proven by the values of the indices of refraction along corres- 
ponding crystallographic axes. Rubidium sulphate is found to be 
quite a unique substance optically, having an extremely low double 
refraction (small differences between the indices of refraction), but, in 
general, a large optical angle (large relative differences between refract- 
ive indices), with high dispersion of the optic axes due to the fact that 
differences in the magnitude of 2 V for different wave lengths are large 
by reason of the extremely small differences between the indices (low 
double refraction). . Similarly the changes in 2 V caused by rise of tèm- 
perature are abnormally large. Further, since the index of refraction 
along crystallographic ¢ increases with rise of temperature faster than 
those along the other axes, and more in amount than the difference 
between the indices alonge and 6 at the ordinary temperature, the 
result is a closing up of the optical angle with a rise of temperature 
and an opening out in the plane normal to its first position, 
The following figures, which are the ratios of the optical elasticities 
along the crystallographical axes, tell this story : 
; Co anD 
At ordinary temperature a : b: e = 0.9991 : 1 : 0.9999 
t b a 
At 180°, d: b: e= 0.9993: 1: 1.0006 
Somewhat similar changes have been found to occur in heating 
potassium sulphate, but only at higher temperatures. The many results 
of this elegant and thorough study can not be given ina review of these 
proportions, and the reader is referred to the original paper. 
Boleite and Nautokite from Broken Hill, N. S. W.—Liver- 
sidge® describes boleite from Broken Hill, N. S. W., in cubic-crystals as 
much as seven millimetres on an edge and modified by both the octa- 
hedron and the dodecahedron. The matrix is hematite and quartz. 
The mineral has heretofore been found only at Boleo in Lower Cali- 
fornia. From the same locality the same writer describes nautokite, 
the lower chloride of copper, in fragments of crystals, and beautiful 
crystals of cerargyrite and cuprite. 
New Minerals from Chili.—The late Dr. Dietze, of Tantal, 
Chili, a few years since studied chemically several new minerals from 
8 Read before the Royal Society of New South Wales, June 6th, 1894. (Sep- 
arate. 
* Zeitsch. f. Kryst., 19, p. 445 (1891). 
