520 
APPENDIX. [ Errors in variation 
meridian, in which case the variation observed was allowed upon the bear- 
ings. But in all other cases it was necessary to find, first what was the 
true variation, and second what it would be with the ship’s head in the 
given direction. 
Example. Suppose that with the ship’s head W. S. W, , the variation 
was observed to be 29° 12' west in the English Channel, where the dip is 
72" north; and I wished to know what variation is to be allowed upon a set 
of bearings taken when the head was N. E. ~ E. 
1st. To find the true variation. 
Dip 72 x ,053 == error for eight points 3°, 816 = (3° 49' =) 229'. 
Course 6 points, distance 229' — departure 212/ or 3° 32' correction. 
Being in north dip, the north end of the needle was drawn forward, that is 
westward in this case, and the west variation observed was too great; there- 
fore 29° 12' observed, — 3° 32' correction = 25° 40' the true west variation. 
2nd. To find from thence what is to be allowed with the head at 
N. E. | E. 
Course 4~ points, distance 229' = departure 177', or 2° 57' correction. 
With the head N. E. ~ E., the north end of the needle at the binnacle would 
be drawn eastward, and the west variation be less than the true ; therefore, 
true variation 25° 40' — 2° 57' = 22° 43' to be allowed, deduced from 29° 12' 
observed. 
This operation will at first seem complex and tedious to the seaman ; 
but vidien a common multiplier is once obtained and the principle of its use 
understood, it will be found not more troublesome than working a me- 
ridian altitude for the latitude ; and the accuracy required is generally 
much less. 
Some persons will be disposed to doubt whether the differences found 
in the azimuths and amplitudes on changing the direction of the ship’s 
head, really took place in the bearings themselves ; a few instances are 
therefore subjoined, in which bearings were taken the instant before tack- 
ing from the shore, and so soon as the ship was round and compass steady, 
the same objects were again set. Differences took place without exception, 
and a ways the same way ; but some of the objects being too near for the 
bearing not to be affected by a small change in the ship’s place, those only 
are selected whose distance was more considerable. The first examples 
