172 Mr. Herschel’s and Mr. South’s observations of the apparent 
y Virginis continued. 
1720.31 Distance “ 7". 49 Cassini. 
1756. o 6. 50 Tobias Mayer. 
1780. o 5. 70 H. The measures of the Cat. for 1782, with allowance 
for the diameters of the stars. 
1820. o 3. 56 Struve, Additamenta. 
1822.25 3. 794 H. and S. ut supra. 
1823.19 3. 300 Amici, Zach. viii. 217. 
This star appears to have undergone a very remarkable 
diminution of distance, and at the same time a material in- 
crease in the mean motion of its component stars one about 
the other. The computed occultation of Cassini in 1720 
cannot have any dependance placed on it, as the lunar tables 
can hardly be supposed correct enough to carry us back 100 
years from the present time, with the precision necessary for 
so delicate an object, unless corrected for that express pur- 
pose by some observations made about the time ; and it may 
fairly be doubted whether the necessary degree of accuracy 
for such observations could then be attained. If we reject this, 
we shall find that a mean motion of o°.66j per annum in the 
direction np sf (or retrograde) will nearly represent the 
measures, as the following statement will show. 
Date. 
Observed Position. 
Calculated Position. 
Difference. 
1756.O 
1781.9 
1803.2 
1820.2 
1822.3 
54°-4 n P 
40.7 
3° -3 
13 -3 
*3-4 
57 -6 np 
40 .3 
26 .2 
14.8 
1 3 -4 
" — 3- 2 
+ 0 .4 
+ 4 - 1 
+ o-5 
0 .0 
The differences are no greater than may well be attri- 
buted to error of observation, while the whole amount of the 
