VOL. Hi. NO. 2sg.

Comess-BY LarLAcE,
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Hon. Henry Meigs, few evenings since, made
the Planetarium by the American Institute a, Ni5-
los Garden upon the subject of Comets In
the course of them he read the following passage
which he translated from the Mechanique Ce-
lcste' of Lapace:


We are certain, says Lsplace, from all the
observations, and above al! from the numerous
comparisons of Maskelyne, which De Lambre
made in order 10 construct the tables of the Sun,
that the Comet OF 1770 did not alter its siderea
year two seconds and eight thirds of time. Hence
we are certain that its mass is not one .fre thou
sandth part of that Of our Earth.


|, results from the calculation Of the preceding
chspter that this Comet harersed the eptirs sys
tenn of the Satellites Of Jupiter, and get 1t docs
not appear to hare caused the slightest 0lteTa-
ton among them


Comets do not sensi6ly disturb the motions of
the Planets by their attractions.-But even if in
the immensity of ages past, some of them have
encountered those bodies, as IS Gerry Pre5c55c, IL
does not appear that tie shock could hare any
great influence.


If one Of those Comets which may have encoua-
tered the Moon or Satellite of Jupiter, had been
of mass equal to our Moon, there is no doub, il
would have rendered their orbits very eccen,ris.


Besides Astronomy presents us two other very
remarkable phenomena which appear to date from
the very origin of the Planetary system, and which
an inconsiderable shock would have caused to dis
appear. mean tie equality Of the rotations Of
the Noon, and The hbrationS Of the three first
Satellites Of Jupiter.


1t is easily seen by the formula contained in the
fifth chapter, as we'll as in the preceding chapter,
that the shock Of Comet of one-,housasdtn of
the mass of the Moon, must have caused very
sible alterations in the real lbrations OF the Moon
and of the Satellites.


We may rest assured, az to the true influence of
Comets, Astronomers have no reason fear any
injury from them to the exactness of their Astron-
omical tables.