MOTION OP THE SUN* Q^ 



tn feeking a folar motion^ which requires the leaft motion Oedudlion of a 

 in the above fix ftars, let ihe line pa, Fig. 1. which reprefents Jj'^^[,'^°J^°';j^'2'^* 

 the real motion, be brought into the fituation ma, and the real real mdtions of 

 motion required will then be at a minim^im. If by the choice *^^"l[^^ '^^^^ 

 of an apex for the folar motion the angle at 5, made by 

 the lines s p and s a, can be letTened, the quantity of real 

 motion required to bring the flar from the paralladic line 

 sp7n to the obferved pofition a, will alfobe diminitbed. 



It has already been fliewn that when two (lars only are given, A fingle line 

 the line sp may be made to coincide with the line sa of both ^^J^^i^^^ of 

 flars, whereby their real motions are reduced to nothing; and rallaftic effeft 

 that when three fiars are concerned fome real motion muft be '" ^^^° ' ^' 

 admitted in one of them. Now, fi nee all parallactic motions are 

 direded towards the fame center, a fingle line may reprefent 

 the direction of the effeft of the parallax. Therefore, letsP 

 orsS, Fig. 2, ftand for the direction of the paralladic motion 

 of the ftars ; and as in the foregoing table we have the angles 

 of the apparent motion of fix ftars, with the parallel of each, 

 the dire^ion of the line s P or sS mufi be computed with the 

 parallels of the fame flars, which may be done as foon as an apex 

 for the folar motion is fixed upon. The difference between 

 thefe angles and the former will give the feveral paralla6)ic 

 angles P sn or Ss a, required for an invefiigation of the leaft 

 quantity, ma, belonging to every ftar. 



The author exemplifies what he here lays down, by fuppofing Computation, 

 the fun to move towards \ Herculis; and calculating the re- ["PP®'^"S tl^s 

 quired angles of the diredion in which the effe6^ of parallax towards ^ Hjt- 

 vvill be exerted with the fix fiars already feledted, he obtains <^'*^*' 

 ■the angles of the parallactic motion with the parallel, the dif- 

 ference between which and the former apparent angles with. 

 the parallel of each ftar gives the angles of the apparent with 

 the paralladlic motion, as reprefented in Fig. 2. The lines s a 

 reprefent the annual quantity of the apparent motions. 



When the fituation of thelaft mentioned angles is regulated 

 as in the figure alluded to, the feveral lines 7/1 a may be drawn 

 perpendicular to S P, and by computation their quantity will 

 be found to be — 



Vol, XIII.*-Januaby, 1805. F Siriu 



