* ee 
; ae 
ee a 
ie f i: . a 3 
120 : Scientific ok 
The following are the angles). as observed with the common. goni- Bis 
ometer i Mr. Hartwell and © by the author. #s 3 
x Hartwell. Author, = oT. ‘gt 
N: a 87° Mita BF aes 
N:; N (att onl 93° 93° 
N:M 188835 133° 30’ 
Rati? 137° 136° 30' 
N tnt 153° 154° 
M : b® Ly 
Ms t? 106°-+107° 
M:P 9°.40° 
M:a 100° 30’ 100° 30’ 
Mesa? 116° *,+ 116° 
M : o! e eRr 
M : o” 140° 
t2.: t? (over P) © 79° 30’ 
eb 140° 139° 45’ 
ER 140° 30’ 
a : a (front) 117° 117° 
The crystallographic wins dancin for the planes are indicated in the 
sm i except for the planes o’, o”, which are not ages: minable “with 
In 
certainty. Naumann’s system of notation they are 
oP @Pma wPo oP P 2P “ig “3Pa2 oe 
N M b a 
Other crystals have since been obtained by Mr. Harwell, one % 
which is six inches long and nearly half this in breadth. The plane 
P, o' and o” are wanting, and the back edge of the plane t? is a ie 
there being no plane—m e complete description of the crystal 
is hence © P, m Po ora. @ P’3, P, 2P, 2P’'@. a plane o P'S 
is seen only on the left side of plane M, as in the figu 
The specimens afforded B. Silliman, sa -» ast Sag ‘iihia react 
These facts set aside an idea adopted by Dufrénoy and Pelou e, and 
(Kobell). And if we consider the protoxyds and peroxyds as replacing 
one another, we find 15 of oxygen in the oxyds to 30 in the silica, 
which is the relation in pyroxene. With the above formula, and Bie 
he B 5 
over 2852 is about three times the corresponding number for bh 
blende, four to four and a half times that of pyroxene and its varieties, 
and twice that of borax. 
