SOLAR MOTION. 279 



This proves eyidently that the mere attraction of Investigation 

 neighbouring stars acting upon each other cannot be the ^oJiJ^ ^of'^hc 

 cause of the sidereal motions that have been observed. sun. 



In the case of supposed periodical binal revolutions of 

 stars about a common centre of gravity, where conse- 

 quently projectile motions must be admitted, the united 

 power of the connected stars, provided the mass of either 

 of them did not greatly exceed that of the sun, would 

 fall very short of the attraction required to give a suffi- 

 cient velocity to their motions. The star Arcturus, for 

 example, which happens to move, as is required, in an 

 opposite direction to the proposed solar motion, were it 

 connected with the sun, and had the proper degree of 

 necessary projectile motion, could not describe an arch 

 of l" of its orbit, about their common centre, in less 

 than 102 years ; and though the opposite motion of the 

 sun, by a parallactic effect would double that quantity, it 

 still would fall short of the change we observe in this star 

 In the course of a single year. 



Other considerations are still more against the admis- 

 sion of such partial connections : thfey would entirely 

 oppose the similarity of the directions of the sidereal mo- 

 tions that have been proved to exist, and which we are 

 now endeavouring to explain. 



Let us then examine in what manner a distant centre of 

 attraction may be the cause of the required motions. By 

 admitting this centr3 to be at -a great distance, we shall 

 have its influence extended over a space that will take in 

 a whole group of ^tars, aid thus the similar directions of 

 their moti-^ns will be accounted for. Their velocities 

 also may be ascribed to the energy of the centre, which 

 may bo sufficiently great for all the purposes of the re- 

 quired motions. A circumstance, however, attends the 

 directions of the motions to be explained, which shows 

 that a distant centre of attraction alone will not be suffi- 

 cient; for these motions, as we may see in Fig. 3, though 

 pretty similar in their directions, still are diverging ; 

 whereas if they were solely caused by attraction, they 

 would converge toward the attracting centre, and point 

 out its situation. It is therefore evident that projectile 

 motions must be combined with attraction, and that the 



motions 



