in the relative Situation of double Stars, See . 3 6g 
requisite should all happen together, to produce the intended 
effect. 
Let the motion of the sun, with the same annual velocity 1, as 
in the case of a. Geminorum, be directed towards x Herculis. 
Then the effect of this motion will show itself at the place of 
y Leonis, in the annual velocity of ,3314, and in a direction which 
makes an angle of 31 0 n' south preceding with the parallel of 
that star. In this calculation, I have admitted the distance of the 
largest of the two stars of y from the sun to be 3, that of a. 
Geminorum being 2. But, if any other distance should hereafter 
be considered as more probable, the calculation may be easily 
adapted to it. The consequence of the parallax thus produced 
on y Leonis in 21,1 years, will be an apparent motion of 2", 788 
south preceding, in the abovementioned direction ; and, on x, it 
will be in the same time, and in the same direction, T',091. As 
the small star must not be too near y, we have, in the calcula- 
tion, supposed it to be at the distance of 4 from O. 
The real annual proper motion of y is required to be 3,5202 ; 
and its direction must make an angle of 3 0 40' north following 
with the parallel. By this motion alone, y would have passed 
over a space of in 21,1 years; but, when it is combined 
with the apparent motion arising from parallax, the star will 
come into its present situation. 
The real annual-motion of x must be 4,6294, in a direction 
o° 20' south following. This will carry it over 9", 74, in 21,1 
years ; and, when combined with the apparent motion which the 
solar parallax will occasion, both together will bring it to its 
proper distance from y Leonis, and to a situation which will 
agree with the last observed angle of position. 
From what has been said, it is again evident, that not only as 
