373 
in the relative Situation of double Stars, &c. 
different powers, is, that with the standard magnifier, 460, and 
the aperture of 6 , 3 inches, the vacancy between the two stars, 
in the year 1781, was i\ diameter of the large star, and that it 
now is 1^. By some earlier observations, the vacancy was found 
to be considerably less in 1779 and 1780 ; but the 7-feet mirror 
then in use was not so perfect as it should have been, for the 
purpose of such delicate observations. By many estimations of 
the apparent size of the stars, I have fixed the proportion of the 
diameter of z to that of x, as 3 to 2. August 31, 1780, the first 
angle of position measured 32 0 19' north preceding;* and, 
March 16, 1803, I found it 44 0 52', also north preceding: the 
motion, therefore, in 22 years and 207 days, is 12 0 33'. It should 
also be noticed, that while the apparent motion of « Geminorum, 
and of y Leonis, is retrograde, that of e Bootis is direct. 
A proper motion in this star, if it has any, is still unknown ; 
our former arguments, therefore, cannot be applied to it, without 
some additional considerations; and, as many others of my 
double stars will stand in the same predicament, I shall give an 
outline of what may be said, to show that this, and probably 
many of the rest, are also binary systems. 
Single Motions . 
(1 a — e) If s Bootis is a star in which no proper motion can 
be perceived, we may infer, from the highly probable motion of 
the solar system, that this star, which is of the 3d magnitude, 
and on that account within the reach of parallax, must have a 
real motion, to keep up with the sun, in order to prevent an 
* The angle of position, in my first Catalogue of double Stars, Phil. Trans, for 1782, 
page 1 15, is 31 0 34' (it should be 54') north preceding. This will be found to be a 
mean of the three first measures hereafter given in a Table of positions. 
MDCCCIIIo 3 C 
