VOL. LXXIII.] PHILOSOPHICAL TRANSACTIONS. 407 



better with the changes of declination of Arcturus and Sirius, which capital stars 

 may perhaps be the most proper to lead ns in this hypothesis. 



It may be expected I should also mention something concerning the quantity 

 of the solar motion ; but here I can only offer a few distant hints. From the 

 annual parallax of the fixed stars, which, from my own observations, I find much 

 less than it has hitherto been counted to be, we may certainly admit that the 

 diameter of the earth's orbit, at the distance of Sirius or Arcturus, would not 

 nearly subtend an angle of 1 second; but the apparent motion of Arcturus, if 

 owing to a translation of the solar system, amounts to no less than 2".7 a year, 

 as will appear if we compound the two motions, of l' 1 1" in right ascension, and 

 l' 55* in declination, into one single motion, and reduce it to an annual quantity. 

 Hence we may in a general way estimate, that the solar motion can certainly not 

 be less than that which the earth has in her annual orbit. 



p. s. In my paper I used a table of the proper motion of some fixed stars, 

 which M. de la Lande has given us as an extract from Tob. Mayer's Opera ine- 

 dita. But I am now furnished with the scarce edition of the original. This 

 work, contains a catalogue of the place of 80 stars, observed by Mr. Mayer in 

 1756, and compared with the same stars as given by Roemer in 1706. From 

 the goodness of the instrument with which the observations, to which Mr. Mayer 

 has compared his own, were made, he gives it as his opinion, that where the dis- 

 agreement in the place of a star is but small, it may be attributed to the imper- 

 fection of the instrument; but that when it amounts to 10 or 15", it is a very 

 probable indication of a proper motion of such a star. He adds, that when the 

 disagreement is so much as in some stars which he names, he has not the least 

 doubt of a proper motion. By this extensive table I thought it highly necessary 

 immediately to examine the hypothesis of the motion of the solar system, that 

 it might receive an early check from observations, if they should be unfavourable; 

 or that, on the other hand, it might be supported by the additional evidence of 

 more stars, if their apparent proper motions should coincide with the idea I have 

 pointed out in my paper on this subject. 



I have followed Mr. Mayer's judgement of his own and Roemer's observations, 

 and left out of the list all the stars that do not show a disagreement amounting 

 to 10" in the places which are given for them in 1706 and 1 756. I have also left 

 out those 13, or rather 14 stars, which have already been examined in my paper, 

 and have been shown to support the hypothesis I have advanced : the rest are 

 here drawn up in 1 tables. The first contains the stars that agree with my as- 

 signed motion of the solar system; or rather which are thereby revolved into ap- 

 parent, or partly apparent, and partly proper motions. The 2d table contains 

 those stars whose motions cannot be accounted for by my hypothesis, and must 



