430 Scientific Intelligence. 
Light from a white cloud was next employed with the same prism, 
the slit having a diameter of =,th of an inch, and being distant from 
the prism about 12 feet. D, F, with three or four of the lines to the left 
of F’, and the strong line in the blue, could thus easily be made out with 
the nuked eye: when magnified by the telescope about forty lines 
could be counted. In each case, the lines were shown to a number of 
none of them would give a defined image by total reflexion, and some 
would scarcely give an image that could be recognized. Sunlight was 
employed, the slit, &e. being as above: to the naked eye one of the 
prisms exhibited five fixed lines, two of the prisms showed four lines, 
four of the prisms showed three lines, four showed two lines, and the 
remaining two showed one line. : 
When the light from a white cloud was used, eleven of these prisms 
showed two lines, viz. F and the strong line in the blue; two showed 
‘three lines, viz. D, F, and the line in the blue. In examining the light 
from the clouds these prisms were not placed at more than four feet 
from the slit. . 
It would seem from these experiments then, that the real difficulty 's 
to find a flint glass prism which will mot exhibit some of the fixed lines, 
provided its dispersive power is sufficiently high. 
New Haven, Feb. 28, 1854. 
Il. Mineratocy anp Geronoey. 
1. Appendix to Observations on the Homeomorphism of some Min- 
eral Species ;* by James D. Dana.—In order to exhibit the true erys- 
tallographic relations of bexagonal and dimetrie mineral species, they 
are presented together in the following tables. The hexagonal species 
in five groups, and the relations of these groups are shown DY the 
symbols of planes at the head of the column. oe 
As dimetric and hexagonal forms are alike in having the lateral axes 
equal, the relation between the crystals of these two systems are | 
shown by the inclination of the base of the prism ona pyramidal plane. 
these angles are the same, since in one system the lateral axes are 90°. 
garded as crossing at angles of 60° and in the other at angles of 9° 
* Page 210 of this yolume. ae 
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