384 Natural-Philosophicat Collections. 
it follows, that the plane determined by M. Laplace may vary, and that thus it 
is not calculated to make known the changes which may in time supervene in the 
position of the planetary orbits and equators. The author therefore concludes 
that, to obtain this result and thus furnish future astronomers with the means of 
comparing in a precise manner the observations separated by long intervals of 
time, it is necessary to have recourse to the plane which he proposes, it being the 
only one which is invariable. He names this plane the Equator of the Planetary 
System. 
Such is the principal result of the new theory which M. Poinsot has presented 
to the Academy. As to the determination of this equator of the solar system, 
the author remarks that it depends, not only upon the masses of the different ce- 
lestial bodies, but also upon the motions of inertia of these bodies with relation 
to their axes, quantities which are as yet unknown tous. The author also ob- 
served, that the question treated by him has two very different objects, the first 
is an important theory, which it is necessary to rectify for the accuracy and im- 
provement of science ; the second is a particular application which supposes the 
measure of certain quantities which time alone and observation can make known 
tous. There results from this, says the author, that the plane in question must 
diter sensibly from that which M. Laplace has determined, because, if the aree 
due to the revolutions of the satellites, oreven to the rotation of the planets, are quan- 
tities so small that they may be overlooked with respect to the others, the case is 
different with the area resulting from the sun’s rotation, which is a large quan- 
tity, and onght uot to be omitted in any case. 7 
Supposing, in the first plaee, the sun to be homogeneous, M. Poinsot finds, 
that the area resulting from the rotation of that great body upon itself, is up- 
wards of fifty times greater than that which the earth describes in the same time 
by its revolving motion in its yearly orbit. If, as is very probable, the density 
is not uniform, but increases from the surface to the centre, in proportion to the 
depth, the author finds that the area in qnestion still amounts to two-thirds 
of the above value. And, even in the supposition that the sun’s density aug- 
ments from the surface where it is null, to the centre where it is infinite as the 
ordinate of a hyperbola approaching the asymptote which is parallel to it, this 
area described would still be half the quantity which it is found to be in the case 
of the sun’s being homoegenecus. Thus, for this hypothesis, which appears ex- 
treme, the resultant of the aree, determined without reckoning this quantity, dif- 
vers as much from the true, as if there had been overlooked in the calculation at 
least twenty-five globes such as our own, which had circulated like the earth at 
the same distance from the sun, but in a plane inclined from seven to eight de- 
grees to the plane of our ecliptie. The author concludes that this omission al- 
ters in a very sensible manner the position of the invariable plane, because it is 
easy to see that it changes by several minutes its inclinatien to the ecliptic, and 
by several degrees the longitude of its ascending node, and that, consequently, 
it is net less necessary in application tnan in theory, to attend to this part of the 
aree which result from the sun’s rotation. It is certain that the only strictly 
invariable plane is that which the auther determines. As to the modifications 
which the constitution of the solar system and the form of the moving bedies 
might authorize, it would be necessary to found them upon a detailed discussion 
of the various elements. The consequences could only be approximative and 
subject to all the limitations which might have been introduced into the caleu- 
lus. 
M. Poinsot proposes to unfold all these considerations in a memoir which he 
intends soon to read to the Academy. 
(To be continued. ) 

On the Aciion of Potassa on Organic Matiers; by M. Gay Lussac.— 
i. Vauquelin, by treating pectic acid with potash in a crucible, converted it into 
oxalate of potassa. This experiment suggested to me the idea of submitting 
