510 MAJOErGENEEAL SABINE ON THE EESHLTS OE HOHEET OBSEETATIONS 
extreme westerly deflection being the same in the solar-diumal variations, and nearly 
opposite to each other in the disturbance-variations. The primary cause of the pheno- 
mena is doubtless the same in both variations ; they manifest alike the influence of the 
solar hours, and are subject ahke to the same alternate periods of increase and decrease 
as the solar spots ; but the mode of action, or the processes by which the effects are pro- 
duced in the two classes, can scarcely be otherwise than dissimilar. It seems probable 
that (omitting for the present the consideration of the magnitudes) the general charac- 
ters of the solar-diurnal variation will be found to con’espond, — e. the hours of the 
easterly and westerly extremes to be the same, — in all the extra-tropical parts of the 
same hemisphere ; whilst in the case of the distui’bance- variation it seems also probable 
that every diversity ia the times of occurrence of the turning-hours may be found in 
different localities. 
In the hypotheses which physicists have framed to account for the times at which the 
solar-diurnal variation changes its direction from west to east and from east to west, it 
has been sometimes supposed that the variable amount of the declination in different 
localities is one of the determining circumstances. The observations at Toronto and 
Point Barrow do not favour this supposition : the dechnation at Point Barrow (taken to 
the nearest degree) is 41° East, and at Toronto 2° West ; there is consequently an angu- 
lar difference in the magnetic direction at the two stations of about 43°, which is nearly 
equivalent to three hours of time in the sun’s azimuth relatively to the direction of the 
needle, whilst the conclusion from the observations in regard to the tuming-hours is. 
that they are the same at Toronto and Point Barrow, or at most have only such small 
diflerences as may reasonably be ascribed to the presence of the small portion of the 
disturbances which we are unable to ehminate. 
With respect to the comparative magnitudes of the range of the solar-diumal mria- 
tion at Toronto and Point Barrow, and to the proportion which the difference in magni- 
tude bears to the difference in the horizontal force of the earth at the two stations, 
we may obtain an approximate conclusion, by comparing the amounts of deflection at 
1 P.M., when the solar-diimial variation at both stations has nearly reached its western 
extreme, and when the influence of the disturbances is nearly at a minimum. The 
deflections at 1 p.m. are 5'T at Toronto, and 8'‘2 at Point Barrow. The absolute values 
of the horizontal force of the earth (which is the antagonistic force to all the min or 
variations, tending to retain the magnet in its mean position) are about 3'63 at Toronto 
and 1'79 at Point Barrow. In accordance with the inverse ratio of these values, we 
should have a deflection of 10', instead of 8'-2, at Point Barrow, as the corresponding 
deflection to 5'T at Toronto. The range observed at Point Barrow is therefore a little 
less than the range which might be computed from the amount of deflection at Toronto. 
But the data upon which the comparison is based, particularly the amount at Point 
Barrow, can only be regarded as approximate, and will by no means justify a more pre- 
