STARS. 



afcenfion only, Arfturus being better fituated to (hew its 

 motion, ought to have it much larger, which we find it has. 

 Aldebaran, both badly fituated and confiderably fn:ialler than 

 the two former, ought to (hew bat little motion. Procyon, 

 better fituated than Sirius, though not quite fo large, (hould 

 have almoll as much motion ; for, on fuppofiug it farther off 

 becaufe it appears fmaller, the effeft of the furt's motion will 

 be led'ened upon it ; whereas, on the other hand, its better 

 fituation will partly compenfate for its greater diftance. 

 I Cygni, very favourably fituated, though but a fmall Itar, 

 (hould (hew it confiderably as well as a, Aquils ; whereas 

 |S Cygni (hould have but little motion ; and y Pifcium, 

 bed fituated of all, (hould have a great increafe of right 

 afcenfion. 



In the laft place, a very (Iriking agreement with the hy- 

 pothefis is difplayed in Caftor and Pollux. They are both 

 pretty well fituated ; and we accordingly find that Pollux, 

 for the fize of the flar, (hews as much motion in right 

 afcenfion as we could exped : but it is remarkable, and 

 feemingly contrary to our hypothefis, that Callor, equally 

 well placed, (hews no more than one half of the motion 

 of Pollux. Now, if we recoUeft that the former is a 

 double ftar, confifting of two ftars not much dilFerent in 

 fize, we can allow but about half the light to each of them, 

 which affords a ftrong prefumption of their being at a 

 greater diftance, and therefore their partial fyftematical 

 parallax ought to be fo much lefs than that of Pollux, which 

 agrees wonderfully with obfervation. Not to mention the 

 great difficulty in which we (hould be involved, were we to 

 fuppofe the motion of Cailor to be really in the (tar ; for 

 how extraordinary muft appear the concurrence, that two 

 ftars, namely, thofe that make up this apparently fingle ftar, 

 (hould both iiave a proper motion fo exactly alike, that in 

 all our obfervations hitherto they have not been found to 

 difagree a fingle fecond, either in right afcenfion or declina- 

 tion, for fifty years together ! Does not this feem ftrongly 

 to point out the common caufe, the motion of the (olar 

 fyftem ? 



As to the quantity of the folar motion. Dr. Herfchcl fijr. 

 gefts the following hints. From the annual parallax of the 

 fixed ftars, which, from oblervations, he finds much lefs than it 

 has hitherto been proved to be, we may certainly admit, that 

 the diameter of the earth's orbit, at the diitance of Sirius or 

 Arfturus, would not nearly fubtend an angle of one fecond ; 

 but the apparent motion of Ardturus, if owing to a tranflation 

 of the folar fyftem, amounts to no Ids than 2". 7 a-year, as will 

 appear if we compound the two motions of i' 1 1" in right 

 afcenfion, and i' 55" m dechnation, into one fingle motion, 

 and reduce it to an annual quantity. Hence we may, in a 

 general way, eftimate, that the folar motion can certainly 

 not be lels than that which the earth has in her annual orbit. 



By confidering the motion of the fatellites round their 

 primary planets, and of the primary planets round the lun. 

 Dr. Herichel is led to fuppoie that the proper motion of 

 the fun is not reftihneal, but that it is performed round fome 

 diftant and unknown centre. Alth ugh we may not ac- 

 quiffce in the hypothefis, that there is any immenle central 

 body of fufficient magnitude to carry round it all the fyftems 

 with which allronomers have filled the regions of fpace, yet 

 we may fuppofe, with M. de la Lande, that there is a kind 

 of equilibrium amang all the fyftems of the world, and that 

 thiy have all a periodical circulation round their common 

 centre of gravity. See Phil. Tranf. vol. xcv. p. 233 — 256. 

 Lalande's Altron.tom. iii. 



The following table contains the proper motion of 36 

 of the principal fixed ftars in right alcenfion and declination, 

 according to the accurate obfervatioiis of Dr. Mftdielyne. 



I 



Table of the Annual Proper Motion of 36 Stars in Righf 

 Afcenfion and Dechnation. 



In the following table we have given the proper motion 

 of nine principal fixed ftars in longitude and latitude, ac- 

 cording to the moit recent oblervations of Dr. Malkelyne, 

 including the preceffion, &c. 



Gatalogu 



