POSITION OF DOUBLE STARS. ^^ 



about Caftor, or rather, the orbits in which they both move Obfervationsanci 

 round their common centre of gravity, are nearly circular, and J-pea'ng^he^' 

 at right angles to the line in which we fee them. If this Ihould change of rela^ 

 be nearly true, it follows, that the time of a whole apparent ftaJ'stxtremel'" 

 revolution of the fmall ftar round Caftor, will be about 342 iiear each other, 

 years and two months. 



y Lconis, 



Our foregoing difcuffions will greatly abridge the arguments 

 which may be ufed, to fliew that this liar and its fmall com- 

 panion are alfo probably united in forming a binary fyftem. 

 But, in order to give more clearnefs to our difquifition, we 

 iliall follow the arrangement which has been ufed with a Ge- 

 minorum, and prefix the fame letters to our paragraphs. 

 Then, if any one article fliould appear to be not fufficienlly 

 explained, we need but turn back to our firft double ftar, 

 where the fame letter will point out what has already been faid 

 more at large on the fubje(5l ; and an application of it may eafily 

 be made. 



The diftance of the ftars y and x, as I fliall again call the 

 fmall one, has undergone a vifible alteration in the lafl 21 

 years. The refult of a great number of obfervations on the va- 

 cancy between the two ftars, made with the magnifying powers 

 of 278, 460, 657, 840, 932, 1504, 2010, 2589, 3168, 4294, 

 5489, and 6652, is, that with theftandard power and aperture 

 of the 7-feet telefcope, the interval in 1782 was J of a diameter 

 of the fmall ftar, and is now |. With the fame telefcope, anct 

 a power of 2010, it was formerly f of a diameter of the fmall 

 ftar, and is now full 1 diameter. In the years 1795, 1796, and 

 1798, the interval was found to have gradually increafed ; and 

 all obfervations confpire to prove, that the liars are now i a 

 diameter of the fmall one farther afunder than they were for- 

 merly. The proportion of the diameter of y to that of x, I , 

 have, by many obfervations, ellimated as 5 to 4. 



The firft meafured angle in 1782, is7** 37'north following*; 

 and the laft, which has been lately taken, is 6° 21' fouth tbl- 



* In my fecond Catalogl^e of double Stars, (Phil. Tranf. for 

 1785, page 48,) the angle of pofition is 5® 24'. This was taken 

 April 18, 1783 ; and, not being acquainted with the motion of the 

 fmall ftar, I fuppofed it to, be more accurat* than the former 

 meafure. 



lowing. 



