24 THE ANTARCTIC MANUAL. 
by the method of vibrations should be obtained on all occasions of the 
ship being swung in harbour, observing the precaution when landing 
the vibration instruments of avoiding positions on land subject to 
local magnetic disturbance. Much value is attached to values of p 
obtained in Antarctic regions when the vibrations are observed on 
ice instead of land for reducing the force observations made on board 
(see below under Total Force). Forms for computing A, » and g, are 
included in those for 6. 
2. Inclination or Dip. 
In order to correct the observed dip, we require to know the 
constants A’, s, d, and V, and the coefficient N, in addition to the 
coefficients B, C, D, obtained for the Fox position when swinging— 
A'=2(1 + sin D) 
ae ee 
CS Oa ain 0) 
These are constant in all latitudes, but should be confirmed by 
observation on large changes of latitude. With the value of s 
already known, coefficient N may be computed from observations 
made at the Fox position by the formule— 
scos +N = {(1—2 sin D) sin {—sin C} cosec &' tan 6’ (2) 
scos¢+N=(cos&+ sin B)secf’tan@® . . . . (3) 
Values of d and V can be calculated by the following formule— 
Vv 
way to 8 Gh = Ay ton Oy 
i » 3096 
AH, + @ tan % = Az = tan 0, — Ny 
In the formule (2), (3), (4), 6 is the observed dip, H and 6 
have the same meaning as in (1), fis the magnetic azimuth of the 
ship’s head. 
Corrections for the deviation of the dip needle from the norma? 
due to the direction of the ship’s head, may be computed by the 
formule (5) or (6)— 
an eS scos€+N be 
or (1 — Z sin D) sin ¢ — sin C = » @) 
ey he SN CC 6 «ox @ & (Bj 
cos €¢+ sin B 
The difference between the values of 4’ so obtained and N being the 
deviation, 
