in the relative Situation of double Stars, &c. 381 
time of a revolution of the small star round $ Serpentis, must 
be about 375 years. 
y Virginis. 
This double star, which has long been known to astronomers,* 
has undergone a visible change since the year 1780, when I 
first began my observations of it. The 21st of November, 
1781, I measured the position of the two stars, which was 
40° 44/ south following. The stars are so nearly equal, that I 
have but lately ascertained the following one to be rather larger 
than its companion ; the position, therefore, ought now to be 
called north preceding. By a mean of three measures, that were 
taken on the 13th of April, 3803, the angle was 30° 20' np. 
The distance, as far as estimations by the diameter can deter- 
mine, when the stars are so far asunder as these are, remains 
without alteration. May 21, 1781, they were 2f diameters 
asunder; and, by estimations lately made, with the same in- 
strument and power as were used 21 years ago, the stars are 
still at the same distance of 2\ diameters. 
A very small proper motion in declination, of o",o2 towards 
the south, has been assigned to this double star ;-f but the quan- 
tity is hardly sufficient for us to rely much upon the accuracy 
of the determination. I shall therefore rather consider y Virginis 
as one of the stars of which we have no proper motion ascer- 
tained; and the arguments to which I shall refer, will conse- 
quently be those which have been given with e Bootis. 
The change of the angle of position, in the time of 21 years 
and 145 days, amounts to io° 24'; from which we obtain the 
* Memoires de l’ Academic des Sciences. Ann, 1720. 
t Connoissance des Temps, Annee VI. page 213. 
MDCCCIII. 3 D 
