EXPLANATION OF THE TABLES. 231 
Parallax at the top and the Latitude at the side; the seconds cor¬ 
responding are to be subtracted from the equatorial hor. par. 
The compression employed is g-J^. 
Table XXXY. Reduction of the Latitude. —This is the difference 
between the latitude as actually found by any astronomical observation 
and what it would be if the earth were a sphere, whichJast is called 
the geocentric latitude. 
To reduce the lat. by observation to the geocentric latitude, subtract 
the reduction of latitude. 
This quantity, which is also called the angle of the vertical , is 0 at the 
equator and at the pole, and is greatest in lat. 45°. 
The compression assumed is g ; that is, the polar radius is supposed 
to be shorter than the equatorial radius by g ^ of the latter. 
Table XXXVI. Augmentation of the Moon's Semidiameter .—The table 
is entered with the Moon’s Semidiameter at the top and her altitude at 
the side; the seconds corresponding are the excess by which her apparent 
semidiameter exceeds that at which it would appear if seen from the 
centre of the earth. 
