and Velocity of the Solar Motion. 225 
A motion of the stars may arise either from their mutual 
gravitation towards each other, or from an original projectile 
force impressed upon them. These two causes are known to 
act on all the bodies belonging to the solar system, and we 
may therefore reasonably admit them to exert their influence 
likewise on the stars. But it will not be sufficient to know a 
general cause for their motions, unless we can show that its 
influence will tend to make them go towards a certain part of 
the heavens rather than to any other. Let us examine how 
these causes are acting in the solar system. 
The projectile motions of the planets, the asteroids, and the 
satellites, excepting those of the Georgium Sidus, are all de- 
cidedly in favour of a marked singularity of direction. We 
may add to them the comet of the year 1682, whose regular 
periodical return in 1 759 has sufficiently proved its permanent 
connection with the solar system. Here then we have not 
less than 23 various bodies belonging to the solar system to 
show that this cause not only can, but in the only case of 
which we have a complete knowledge, actually does influence 
the celestial motions, so as to give them a very particular 
appropriate direction. Even the exception of the Georgian 
satellites may be brought in confirmation of the same pecu- 
liarity ; for though they do not unite with the rest of the 
bodies of our system, they still conform among each other to 
establish the same tendency of a similar direction in their 
motion round the primary planet. And thus it is proved that 
the similar direction of the motion of a group of stars may be 
ascribed to their similar projectile motions without incurring 
the censure of improbability. 
Let us however pursue the objection a little farther, and as 
MDCCCVI. G g 
