in the relative Situation of double Stars. 36 1 
allowed to have, will carry it, in an angle of about degrees, 
towards the south-preceding part of the heavens ; but the motion 
assigned to it in the new Tables, has a direction towards the 
north. Hence it follows, that « Herculis has also a real motion, 
which, by its composition with the parallactic one, produces the 
tabular apparent one. 
We are now to examine the effect of these three motions, on 
the position of the two stars of our double star, in order to see 
how far they will account for the observed change. The two 
stars are sufficiently different in magnitude, for us to expect a 
difference of parallax, on a supposition that their distances from 
us are inversely as their apparent magnitudes. The change of 
the angle of position, arising from a superior parallactic motion 
of the large star, would have occasioned a retrograde motion of 
the small one ; but this, by my observations, has moved accord- 
ing to the order of signs ; its change of situation, therefore, will 
admit of no explanation from the effect of parallax. 
The real motion of « Herculis, being such as, with the union 
of the parallactic one, will produce an apparent motion towards 
the north, is determined by the velocities and directions ol the 
other two motions. It must however be towards the north- 
following part of the heavens, and of a velocity considerably 
greater than the proper motion given in the new Tables ; but, 
since it is known to be compounded with the parallactic one, 
we are now only to consult the direction and velocity of that 
•composition, which is such that the large star, in 23 years and 
14 days, must have been carried 5A299 towards the north. If 
the stars are not connected, the most favourable case we can 
put, will be to. suppose the small one at rest, and at such a dis- 
tance from us as to be intirely free from sensible parallax. 
3 A 2 
