444 
The Centre of Gravity of the Earth , [August, 
c T and c r the direction of two stars, the sum of whose 
declinations equal the angle TCR. The declination of the 
star T would be obtained by subtracting its polar distance 
from 90°, and the declination of the star R obtained in the 
same manner. 
Diagram i. 
The observer at the North Pole, P, would find his zenith 
in the direction of G p produced, G being the centre of gravity 
of the Earth, whereas the true zenith of P would be in the 
direction of c p produced. From p draw pt' parallel to c T, 
and the zenith distance of the star T would, by observation 
at the pole p, be N pt'. Consequently this zenith or polar 
distance would by observation be too great by the amount of 
