230 Scientific Intelligence. 
hg iat 
and examined optically, showed that it was penetrated irregularly 
that the true composition can be obtained only from crystals 
whose composition has been most certainly determined. ' 
For the sake of comparison tlie results obtained by the wnter 
agree very closely with them. : ‘th 
Type LU, monoclinic ; angle made by plane of optic axes W! 
the base 25° 50’ (about 30°, DesCloizeaux). Bisectrix pa 
normal to the plane of symmetry, 2Ha (red rays) =88" 48 (86 
-87° 20’, DesCloizeax). kis 
Type III, monoclinic; angle made by the plane of the op 
axes with the base about 73° (11° DesCloizeaux, humite). sad 
e red angles upon the Brewster crystals, as was hy et 
were inconclusive except as proving that the obliquity sh 
exceed a very few minutes. How small the variation eso 
rectangular form is for crystals of the second type, 4 ph Jes: 
DesCloizeaux, may be judged from the following pairs © ' ae 
Ajne?=109° 5’, AAvc?’=108° 58; AAr _ 28; se 
113° 25’, ete.; if the crystals were orthorhombic, as vy angles 
assumed, the planes e? and e?’ would be identical, and t oe the 
on the base A would be the same; so also for r and 7* " som the 
third type DesCloizeaux makes the monoclinic variation of 
rectangular form about ¢wo minutes. Some additional ewitll 
te recently obtained from bre 
3=113 
TAvV LeonnarD. 3d ed. 65 pp. 8vo. Stuttgart, 1876. poner 
Duchy of Baden is remarkable for the variety and abun by 
the minerals which it affords. This is explained, a = 
