199 



two, yet, in doing this, we must assign a high degree of real motion, 

 to Capella. To this it may be objected, that we have no reason to 

 deprive Arcturus and Sirius of real motions, in order to give a motion 

 of the same nature to every star that has a proper motion not tending 

 to the same parallactic centre as the motions of Arcturus and Sirius. 



It appears, therefore, that such an apex for the solar motion ought 

 to be fixed upon as is equally favourable to every star that is proper 

 for directing our choice ; and our aim must be, to reduce the proper 

 motions of the stars to their lowest quantities. 



From a table given by Dr. Herschel, it appears, that the sum of 

 the apparent motions of the six principal stars whose intersecting 

 arches are given, namely, Sirius, Arcturus, Capella, Lyra, Aldebaran, 

 and Procyon, is 5"'353 ; and if we suppose the point towards which 

 the sun moves to be A Herculis, the annual proper motions of the six 

 stars will be reduced to real motions of no more than 2"'219. 



It appears, from the inspection of a figure that represents the 

 quantities of real motion required when A Herculis is fixed upon, 

 that, by a regular method of approximation, a situation might be 

 found where the apparent motion of the six stars would be much re- 

 duced. Accordingly, by fixing upon a point near the following knee 

 of Hercules, whose right ascension is 270 15', and north polar di- 

 stance 54 45', the annual proper motion of the six stars was reduced 

 to l"-459, which is 0"'760 less than when the apex was A Herculis. 



In approximating to the above point, the line of the apparent mo- 

 tion of Sirius was principally considered ; but, as Sirius is not the 

 star that has the greatest proper motion, it occurred to Dr. Herschel 

 that another minimum, obtained from the line in which Arcturus 

 seems to move, would be more accurate ; and he was soon led to a 

 point, not only in the line of the apparent motion of Arcturus, but 

 equally favourable to Sirius and Procyon, the remaining two stars 

 that have the greatest motion. The right ascension of this point is 

 245 52' 30", and its north polar distance 40 22'. 



If the principles which have been laid down for determining the 

 solar motion are admitted, the above apex must be very near the 

 truth ; for an alteration of a few minutes in right ascension or polar 

 distance, either way, will increase the required real motion of these 

 stars. The sum of the real motions with the before-mentioned apex 

 is only -859, being less than that of the former calculation by '599. 



Dr. Herschel does not, he says, mean to assert that these real mo- 

 tions can be actually reduced to the low quantities above mentioned ; 

 but, whatever may be the sum of real motions required to account 

 for the phenomena of proper motions, the foregoing arguments can- 

 not be affected by the result ; for, as it is known that proper motions 

 exist, and no solar motion can resolve them entirely into parallactic 

 motions, we ought to give the preference to that direction of the 

 motion of the sun that will take away more real motion than any 

 other. 



