other. 



q<20 CAirSfi 6F THE CHANGE Of RELAYlVE 



ObiVrvatlons according to Mr. De la Lande's account*, we fliould alftf 



and intcrctces /- , , , . ,,.,,.. , . . 



re(pc ajng he confider the annua! proper motion or » m decimation, which 

 changes otte- \g gjveii 0'',]2 towards the north, we lliall find, by entering 



lative fituation rr-. i i • ■ • .• Tk.T . ^'/„^ .i ^ xl^ 



in ftars extreme- ^""^ Table with the motion «tN, amountmg to 2 82, that the 

 !y near each. diftance oF the two ftars will bo ftill more' diminifhed ; but 

 that, on the contrary, the angle of pofition will be much 

 lelfened ; and, by combining the two motions together, the 

 apparent difks of the two flars fliould now be a little more 

 than one-tenth of a fecond from each other, and the angle of 

 pofition 35 degrees fouth preceding. But, fince neither -of 

 thefe effects have taken place, the hypothefis cannot be ad- 

 mitted. 



(c) That the fun has a proper motion in fpace, I have fliown 

 / with a very high degree of evidence, in a paper which was 



read at the Royal Society about twenty years ^go f . The fame 

 opinion was before, but only from theoretical principles, 

 hinted at by Mr. De la Lande, and alfo by the late Dr. Wilfon, 

 of Glafgow + ; and has, fince the publication of ray paper, 

 been taken up by feveral afironomers^, who agree that fuch 

 motion exifts. In confequence of this, let us now, according 

 ia No. 3. affign to the fun a motion in fpace, of a certain 

 velocity and dire6tion. Admitting therefore a, and x to be at 

 teft, let the angle PaO be 90 degrees; then, by ihe ift cafe 

 ot No. 3, we find that none of the obferved changes of the 

 angles of pofition will admit of an explanation. There is 

 moreover an evident conceiTion of the point in queftion, in 

 the very fuppofition of the above angle of 90 degrees ; lor, if 

 a? be at the fame diftance as a from the fun, and no more than 

 5'' from that ftar, its real diftance, compared to that of the fun 

 from the ftar, will be known; and, fince that muft be lefs 

 than the 40 thoufandth part of our diftance from Caftor, 

 thefe two ftars muft neceflarily be within the reach of each 

 others altradion, and form a binary fyftem. 



(d) Let us now take the advantage held out by the 2d cafe 

 of No. 3, which allows us to place x far behind a ; in which 



* See page 21 1 of the treatife before referred to. 



t Philof. Tranf. vol. Ixxiii. p. 247. 



J See my note in Phil. Tranf. vol. Ixxiiii p. 283. 



§ See jiJJronomiJhes Jahrhuch fur das Jahr 1786; feite 259. 

 Ubir die fortruckung unferes Sonnen-Syjiems, von Herrn Fffejfor 

 Prcvoft. IJnd fur das Jahr 1 ^0^, feite 113, 



fituation 



