1881.J and its Effect on Astronomical Observations. 511 
12 hours right ascension of the South Pole of annual rota- 
tion. The point A will be the position of this pole on 
January 1st ; B its position on February 1st ; and so on. 
If the annual rotation did not occur the pole N would, during 
the year, move down the arc N A. But the pole N rotates 
Diagram 4. 
Apparent Curve traced by the Zenith of the South Pole annually, due to 
the position of the Centre of Gravity of the Earth. 
round the moving centre, A, B, c, &c. ; so that the pole N 
moves to o during January, to P during February, to q 
during March, and so on, reaching the point near a on 
December 31st. The accuracy of this curve can now be 
tested by the aid of southern stars near the South Pole of 
the Heavens. 
The first star we find in the “ Nautical Almanac ” having 
