82 Mr. Robertson on the Precession of the Equinoxes. 
5400 Log. 3.7323938 1465 - Log. 3.1658376 
3 Log. 0.4771213 53361 - Log. 4.7272240 
461 Log. 2.6637009 7.8930616 
55.042878 Log. 1.7407010 
8.6139170 
7.8930616 
0.7 208554 — Log. of 5". 2584. 
Consequently the annual precession, caused by the disturbing 
force of the sun, is 21 ".0336. 
The obliquity of the ecliptic has been assumed as equal to 
2 3° 2 7* 4 5", such being its magnitude, very nearly, at the 
beginning of the year 1807. 
From the general expression 360 x x obtained in 
article 24, it is evident, that when the sun is in either of the 
equinoctial points, the nutation becomes equal to o. Supposing 
therefore the earth to be subject to no other disturbing force 
than that of the sun, at each of the equinoxes the earth’s 
diurnal revolution is made about its axis of figure, as PL in 
Fig. 9 ; but as at other times the disturbing force tends to 
cause a libration about a diameter of the equator, it is evident 
from article 10, that the axis about which it revolves deviates, 
by a quantity extremely small, from its axis of figure. A 
similar deviation, of the axis of revolution from the axis of 
figure, is produced by the action of the moon ; but a minute 
examination of these deviations is foreign to the present 
design. As the foregoing articles extend beyond the supposed 
difficulty in the subject, it is deemed unnecessary either to add 
to their number, or to lengthen this Paper by such additional 
remarks, as may be met with in every respectable publication 
on Physical Astronomy. 
