410 Scientific Intelligence. 
pletely opposed to each other. — Thus in the hyposulphates of lime, 
ul the 
direction of the greatest and sometimes that of the least elasticity. In 
elasticity. ‘These properties have enabled the author to produce united 
crystals which exhibited very remarkable optical phenomena. Thus the 
hyposulphate of strontia united in progressively increasing proportions 
ith hyposulphate of lead, gives a series of salts in which the double re- 
fraction at first becomes enfeebled and then reappears with a contrary 
sign, so that we find toward the middle of the series, mixtures which 
behave like hyposulphate of lead for one extremity of the spectrum and 
like hyposulphate of strontia for the other, while for the intermediate 
part there is no double refraction. Very remarkable phenomena are 
The violet and axes again separate, but the red always moving 
more rapidly than the others are then less separated. The dispersion 
Is now the inverse of what it was originally, and the rings are re 
within and blue without. Finally, an instant arrives at which the red 
salt with reference to the violet axes, while it has but a single axis for 
the intermediate colors. Finally, as the influence of the ammonia salt 
increases the violet axes pass like the red into a plane at right angles 
cal species. The author directs attention to the fact that physical inves 
tigation is in advance of chemical analysis as respects topaz; and that 
an accurate study of the micas will probably lead to the discovery of 
. “4 ia 7 
metral planes at right angles to each other, subsequent commun 
cation the author gives the result of an examination of forty-five spe 
cies of mica by which he obtained a complete confirmation of his pre- 
