388 Prof. von Kobeli’s Stauroscopic Observations. 
Art. XLUI—An Abstract of Prof. von Kobell’s Stauroscopic 0b. 
servations; by OGDEN N. Roop, Professor of Chemistry in 
Troy University. 
eye at EH, Sis the stage-plate or 
ing tourmaline. During the ex- i et 
periments the stage-plate S with the crystal is revolved a 
the axis EP, the rest remains stationary. Y 92 5a 
I have found it much better to use two Nicol’s prisms it 
stead of jhe glass plate and the tourmaline, and in my oy 
experiments at the end of this article they were employed & 
clusively. de ie: 
The plate of cale spar being in its proper position, the Fine 
maline is turned so as to darken the fie d, and upon ie 4 
of the engraved square coincide in position with 
tourmaline. If it be wished to determine the ory 
planes) in which the polarized rays of a double bemere” ovat 
tal vibrate with regard to the edges of the observ 
]- 
el with one of the sides of the engraved square, be beh 
Cis (See von Kobell’s “ Mineralogie,” 2nd edit. 1858, p- 4i. 5 
x + Vol. xix, 2nd Series, p. 425, and xx, 415. a’ 
t 
