SOLAR MOTION, 239 



and its velocity. The changeable part will consist of the investigation 



angular quantity of the real motion, the parallactic direc- °^ ^^^ proper 

 ^. - , . f , . , . ' * inotion of the 



tion of this motion, and its velocity. sun. 



Before we can make a calculation of the required velo- 

 cities, we must fix upon the probable relative distance of 

 the rest of the stars, in the same manner as we have 

 done with the first six. In this 1 have thought it advisa- 

 ble to distinguish the stars that, from their lustre, may be 

 called principal, and have limited their extent to the 

 brightest of the second magnitude, on account of the un- 

 certainty which still remains about their progressive dis- 

 tances. For though it appears reasonable to allow that 

 the bright stars of the second magnitude may be twice as 

 far from us as those of the first, it will admit of some 

 doubt whether this rule ought to be strictly followed up 

 to the 3d, 4th, 5th, and 6th magnitude j especially when 

 it is not easy to ascertain the boundaries which should 

 limit the magnitudes of very small stars. 



The number of these principal stars is 24. The re- 

 maining 12 are also arranged by admitting that their mag- 

 nitudes express their relative distances; and notwith- 

 standing the doubtfulness we have noticed, their testimony 

 with respect to the proper quantity of a solar motion, 

 though it should be received with some diffidence, must 

 not be neglected ; some considerable alteration in their 

 supposed distances, however, would have but little effect 

 upon the conclusions intended to be drawn from their 

 velocities. 



The following Table contains the result of the calcula- 

 tions that relate to the permanent quantities. In the first 

 and second columns, we have the names of the stars, and 

 their assigned relative distances. The third gives the 

 apparent angular motions, and the fourth their direction. 

 The fifth contains the direction of the same motions, with 

 respect to the parallactic motions arising from the given 

 solar direction ; and the sixth gives the velocity of the 

 stars which produce the quantity of the apparent motions. 



I i 2 Table 



