Page:Proceedings of the Royal Society of London Vol 1.djvu/248

Rh to a greater equality among each other, it will be a very proper se- condary consideration.

The necessary calculations for investigating the solar motion may, our author says, be divided into two classes: the ﬁrst of these will remain unaltered, whatever may be the solar motion under examina- tion; while the other must be adjusted to every change that may be required. The ﬁrst will contain the angular quantity of the observed or apparent motion; its direction with the parallel of the star; its direction with the parallactic motion; and its velocity : the second. or changeable part, will consist of the angular quantity of the real motion ; the parallactic direction of this motion ; and its velocity.

A table containing the result of the calculations relating to the permanent quantiﬁes of 36 stars is now given : there are also va- rious ﬁgures illustrating the said calculations : upon these, various remarks are made, which cannot be well understood without a view of the ﬁgures. We shall only observe, that several stars of the ﬁrst magnitude appear to have less velocity than many which are much smaller. This, Dr. Herschel thinks, may be explained, if a solar motion is introduced; as the parallax arising from that cause Will completely account for such a singular circumstance. He adds, that if the foregoing argument proves the expediency of admitting a solar motion, the direction of that motion is no less evidently pointed out to be in opposition to the motion of Arcturus.

By equalizing the velocities of the sun and a Orionis, the solar motion appears to be l"'266. On the other hand, by a similar cal- culation of the velocities of Pollux and the Sun, those velocities will be equalized by a solar motion of 0"'967. These seem to be the limits of the solar motion, upon the supposition of its holding a middle rank among the sidereal velocities: and, by a mean of them, we may have the rank of the solar motion true to less than 0”-15. Upon this supposition, a table of the changeable quantities above mentioned is given, and also figures illustrating them.

. Dr. Herschel, after observing that, if we except only ten of the above-mentioned stars, all the rest appear to be actuated by the same inﬂuence, and, like the sun, to direct their motions towards the same part of the heavens, proceeds to examine the causes of this marked singularity in their direction; which. he says, may arise either from their mutual gravitation towards each other, or from an original projectile force impressed upon them. As both these causes are known to act on all the bodies belonging to the solar system, they may reasonably be supposed to exert their inﬂuence likewise on the stars : and that this is really the case, our author endeavours to show by various arguments, which our limits necessarily oblige us to omit. He shows that the motions of the stars already men- tioned cannot be accounted for by the mutual gravitation of neigh- bouring stars towards each other, or by a periodical binal revolution of them about a centre of gravity; but that we ought rather to have recourse to some far distant centre of attraction; which centre may