536 
Mr. Christie's theory of the 
of 15° in the angular position of the poles relatively to the 
meridian, corresponding to their positions at intervals of an 
hour throughout the day, are contained in the opposite Table, 
The time indicated in the first column is that elapsed since 
the magnet having its north pole upzvards, which represents 
the noj'th pole near the equator on its northern side, was on 
the northern true meridian: and in the following columns 
are indicated the deviations of the north end of the needle, 
from the magnetic meridian, at the respective hours, and 
under the circumstances indicated above the several columns. 
The magnet having its north pole upwards was considerably 
stronger than the other. When this magnet was on the 
southern meridian, that which had its south pole upwards 
was to the east of it; the angular distance between the poles 
is indicated above the columns containing the deviations of 
the needle. It is scarcely necessary for me to mention, that 
had I adjusted the compass and the magnets so that the 
deviations should not have exceeded the observed diurnal 
variation, I should not have been able to observe the effects 
with any precision : the adjustments therefore were made so 
that the deviations should greatly exceed the diurnal changes. 
The deviations in each set are only comparable among them¬ 
selves. 
In order to compare the deviations corresponding to differ¬ 
ent hours, reckoned from the passage of the north pole over 
the true north meridian, with the observed changes in the 
direction of the needle at different times in the day, it is ne- 
cessar}' to assign some particular time in the day for that 
which is taken as the zero in this table. Considering that 
the diurnal changes have been most accurately observed by 
