382 Vr. Herschel's Account of the Changes , &c. 
annual motion of 29', 16. The observed and calculated angles* 
with their differences, on which it will not be necessary to make 
any remarks, are in the following Table. 
Times of the observations. 
Observed 
angles. 
Calculated 
angles. 
Differences. 
Nov. 21, 1781 
°o 
"f. 
4°° 44* 
o° o' 
Jan. 29, 1802 - 
28 22 
3° 51 
— 2 29 
April 15, 1803 
30 20 
00 
0 
ta 
O 
O O 
May 28, 1803 
32 2 
30 17 
+ 1 45 
As a confirmation of the accuracy of these observations, we 
may have recourse to a position of the same stars, deduced from 
the places of them, as they are given in Mayer's Zodiacal 
Catalogue. By two observations, reduced to the beginning of 
the year 1756, the preceding one was 3", 8 before the other in 
right ascension, and 5", 3 more north than that star. From this 
we calculate the position, which was 54 0 21' 37" north preceding. 
The interval from the 1st of January, 1 756, to the 21st of No- 
vember, 1781, is 25 years and 325 days. When this is added to 
the period I have given, we have 47 years and 105 days, for a 
motion of 24 0 2'. The annual motion, deduced from this 
lengthened period, which is 30^5, differs less than ii minute 
from that which has been calculated from my observations. 
With the assistance, therefore, of Mayer's observation, which 
greatly supports our calculation, we may conclude, that the two 
stars of y Virginis revolve round each other in about 708 years. 
