229 



be either a single body of great magnitude ; or it may be produced 

 by the joint attraction of a great number of stars united into one 

 condensed group ; or, lastly, it may be formed by the union of several 

 groups, which, he says, will create a still more powerful centre of 

 gravitation. 



Dr. Herschel now proceeds to the determination of the quantity 

 and velocity of the solar motion : and, calculating upon the principles 

 laid down in the course of the present paper, assuming, as we have 

 already stated, that the solar motion holds a middle rank among the 

 sidereal velocities, it appears that we have sufficient reason to fix 

 upon the quantities of the solar motion to be such as, by an eye 

 placed at right angles to its direction, and at the distance of Sirius 

 from us, would be seen to describe annually an arch of 1-116992 of 

 a degree ; and its velocity, till we are acquainted with the real 

 distance of the fore-mentioned star, can therefore only be expressed 

 by the proportional number of 1116992. 



Before he concludes, our author remarks, that the middle rank 

 among the sidereal velocities, which he has assigned to the sun, 

 agrees sufficiently with the phenomena that were to be explained. 

 Thus the apparent velocities of Arcturus and Aldebaran, without a 

 solar motion, are to each other as 208 to 1 2 ; but, according to the 

 assumed solar motion, it appears, that when the deception arising 

 from the parallactic effect is removed, these velocities are to each 

 other only as 179 to 85, or 2 to 1. And although Arcturus still 

 remains a star which moves with great velocity, yet it has been 

 shown, in the eleventh table, that we have three or four stars with 

 nearly as much motion, and five with more. The solar motion also 

 removes the deception by "which the motion of a star, of the conse- 

 quence of a Orionis, is so concealed as hardly to show any velocity ; 

 whereas, by computation, we find that it really moves at a rate which 

 is fully equal to the motion of the sun. 



It will now be found, Dr. Herschel says, that we are within the 

 reach of a link of the chain which connects the principles of the 

 solar and sidereal motions with those that are the cause of orbitual 

 ones : the probable motions of the sun and of the stars in orbits 

 consequently becomes a subject that may receive the assistance of 

 arguments supported by observations. And he further observes, that 

 what he has said in a former paper, where the sun is placed among 

 the insulated stars, does not contradict the present idea of its form- 

 ing a part of a very extensive system. The insulation there ascribed 

 to the sun relates merely to a supposed binary combination with 

 some neighbouring star ; and it has been already proved, by the 

 example of Arcturus, that the solar motion cannot be occasioned, or 

 accounted for, by a periodical revolution of the sun and the above, or 

 any other star, about their common centre of gravity. 



