Astronomy. ~~ 277 
The equilibrium of the body of a fish in the water is independent of 
the natatory bladder; this organ even interfere with it; as 
the fish lies in its horizontal position with the back upwards, it depends 
solely on the action of the , and principally on the vertical fins, 
its specific gravity. — By compressing the air which is contained in it, 
the fish descends in the water; and it rises again by relaxing the muscles 
which had served to compress the bladder. Moreover, the fish may 
remain at the bottom of the water, by the very fact of the pressure of 
~~ column . water on the air contained in the bladder. 
y compressing more or less the posterior portion or the anterior 
portinen of sie bladder, the animal is able to render the anterior half or 
the posterior half of its body lighter at will; it can also take an o oblique 
position, which allows a movement of rising or of escending in the 
to favor this action. ‘The Cyprinoids and the Characi have two blad- 
ders, one before the other, communicating with one another by a narrow 
tube 
bes slightly so; and in proportion as the fish rises in the water, the ante 
rior bladder, which is the most elastic, must considerably increase in vol- 
ume, and thus keep the head of the animal up, W whilst the contrary must 
be the case when the fish descends.—Mitller’s Archiv, 1845, p. 
¥ 
lV. Astronomy. 
1. On the e Attempts to explain the Projection ofa a Star on the Moon, 
during an Occultation ; by Prof. Powexn, (Brit. A from the At 
hy Sept. 26, 1846.) —Some remarks having been i biougi forward at 
e last meeting, relative to the singular phenomenon above named, in 
which “ diffraction” was referred to as, at least, in a general sense, likely 
the question. “ Diffraction” has often been appealed to in cases apparently 
of the Swe class; but, in the more strict and limited sense of the term, 
it cannot apply, since both the conditions and the resulting phenomena 
appear essentially different. The phenomena properly ascr ribed to “dif 
fraction” exhibit fringes,—and suppose the edge of the intercepting iid 
to be within the area of the rays. But there are some effects 
comitant kind, which have been less attended to. One of the most re- 
markable of these is that deaaeed by Newton, (Opts book iii, part i, obs. 
» 6, 7,) in which the light admitted ace a pris mgroiat e ter of an 
inch in diameter, falling on the edge of an opaque body, es the phe- 
nomena since culled “ diffraction,” gave rise to long eke ry or “‘ trains 
of light darting into the shadow perpendicular to the edge, shown on a 
