238 - SOLAR MOTION. 



Investigation It must be evident from what has been said, that a cer- 

 of the proper ^j^j^ p^^jj^p ^3^^^ ^j. ^riiddle rank, should be assigned to the 

 sun. motion of the sun, unless very suflicient reasons should 



induce us to depart from this condition. To obtain thit 

 end must consequently be our principal aim ; and if wo 

 ' can at the same time bring the sidereal motions to a great- 

 er equality among each other, it will certainly be a very 

 proper secondary consideration. 



There are two ways of taking a mean of the sidereal 

 motions, one of them may be called the rate and the 

 other the rank. For instance, a number equal to the 

 mean rate of the six numbers, % 6, 13, 15, 17, 1 9, would 

 be 12 ; but one that should hold a middle rank between 

 the three highest and three lowest of the six would be 14. 

 In assigning the rate of the solar motion it appears to be 

 most eligible that it should hold a middle rank among the 

 sidereal velocities. We shall however find that nearly 

 the same result will be obtained from either of the 

 methods. 



With respect to our second consideration, w^e may see 

 that it also admits of a certain modification by the choice 

 of the solar motion ; for in Table IX. when this motion is 

 1",5 the velocity of Arcturus 1565735, will exceed that 

 of Sirius, 217007, more than seven times; whereas a 

 solar motion of l" will give us the proportional velocities 

 of these stars as 188867 to 465174; and the former will 

 then exceed the latter only four times. 



Calculations for druwing Figures that Kill represent the 

 oljserved Motions of the Stars. 



The necessary calculations for investigating the solar 

 motion are of considerable extent, and may be divided 

 into two classes, the first of which will remain unaltered 

 whatsoever be the solar motion under examination, while 

 the other must be adjusted to every change that may bo 

 required. 



The direction of the sun remaining as it has been settled 

 in the first part of this Paper, the permanent computa- 

 tion of each star will contain the annual quantity of the 

 observed or apparent motion, its direction with the pa^ 

 rallel of the star, its direction with the parallactic motion, 



and 



