250 Dr. Herschel on the Direction of the 
that when two stars only are given, the line sp may be made 
to coincide with the lines sa , of both the stars, whereby their 
real motions will be reduced to nothing. It has also been 
proved, by adding Capella to the former two, that when three 
stars are concerned, some real motion must be admitted in one 
of them. Now, since all parallactic motions are directed to the 
same center, a single line may represent the direction of the 
effect of the parallax, not only of these three stars but of 
every star in the heavens. According to this theory, let the 
line sP or sS, in Fig. 2, stand for the direction of the paral- 
lactic motion of the stars ; and as in the foregoing Table we 
have the angles of the apparent motion of six stars with the 
parallel of each star, we must now also compute the direction 
of the line sP or sS with the parallels of the same stars. This 
may be done as soon as an apex for the solar motion is fixed 
upon. The difference between these angles and the former 
will give the several parallactic angles P sa or Ssa, required 
for an investigation of the least quantity ma, belonging to 
every star. 
For instance, let the point towards which we may suppose 
the sun to move, be x Herculis ; and calculating the required 
angles of the direction in which the effect of parallax will be 
exerted, with the six stars we have selected for the purpose of 
our investigation, we find them as in the following Table. 
