228 



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 quantities 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 1"'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 O ri '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 



