110 Scientific Intelligence. 
he has been able, by comparing a nebula with some small star 
near it, and repeating this comparison after a certain time, to 
show slight differences of distance or of position which might 
indicate a proper motion of one or the other of these heavenly 
bodies. : 
I here terminate this brief review, in which I have been able 
to give only a hasty glance at the actual labors of observers 
upon one of the more difficult and less advanced portions of 
astronomical science. y 
.S. M. d’Arrest announces, in No. 1378 of the “ Astronom- 
ische Nachrichten,” that he has recognized in the constellation 
Taurus the existence of a second nebula of variable brightness. 
SCIENTIFIC INTELLIGENCE. 
I. PHYSICS. 
1. On a new form of Spectroscope, (from a letter of Dr. Woxcort 
Gress to B. Striman, Jr.)—* Messrs. J. and W.G 
opticians of this city, have just completed, at my suggestion, a spectroscope 
ts of this kind. In this instrument the prism of flint glass has a re- 
fracting angle of only 37°: the rays which diverge from the slit are ren- 
dered parallel in the usual manner by an achromatic Jens having the slit 
in its principal focus. The bundle of rays then falls upon the first surface 
of the prism at a perpendicular incidence, and of course makes an angle 
of 37° with the second surface. Under these circumstances the refraction 
takes place at an angle so near the limiting angle that the refracted rays 
emerge nearly parallel to the second surface of the prism. The amount 
of dispersion produced in this manner is very great, while the loss of light, 
oceasioned by reflection at the first surface in prisms of 60° placed 10 
the position of least deviation, is avoided. The spectrum thus produced 
esses remarkable intensity and the dark lines aré seen in countless 
numbers and with great distinctness. The instrument in this form is sub 
ficient for all chemical purposes, but it is so constructed as to permit the 
use of i gt 
