337 
diurnal variation of the magnetic needle , &c. 
Canton and Colonel Beaufoy, in London and its vicinity, I 
shall determine this from their observations. It appears from 
these, that the maximum west variation happens about i h 3o m 
P. M. Now, in the table, when the variation is 19 0 W., or 
24 0 40' W., this maximum corresponds to about i3 h 30™, or 
i3 h 2o m after the north pole has passed the northern me- 
ridian. So that the hours in the first column of the table 
must, in all cases, nearly indicate the times since midnight. 
This being the case, it will be seen, that when the angle be- 
tween the poles is 130°, the times of the maxima, and the 
characters of the deviations, in the respective cases, approxi- 
mate to the observations at Fort Enterprise, in London, and at 
Port Bowen, and perhaps as nearly as we ought to expect, 
when we consider that, admitting the correctness of the hy- 
pothesis, many circumstances in the experiment must neces- 
sarily be different from those accompanying the phenomena 
in nature. But to form a more just estimate of the nature of 
the agreement, I shall point out the principal discordances 
and coincidences between these results and the observed 
diurnal changes. I may premise, that, whether the poles 
revolve in the interior of the sphere, on the surface of which 
the needle is supposed to be situate, on its surface, or exterior 
to it, the character of the changes which take place in the 
direction of the needle is nearly the same. I will, however, 
for the purpose of comparison, take the case where the poles 
and the needle are at the same distance from the centre. 
Observations at Fort Enterprise. Lieutenant Hocd states 
that the maximum east variation occurred at 9 h A. M., but 
the first observations in the morning which are given for 
January and February, were at io h A. M., and none are 
mdcccxxvii. X x 
