72 Connexion between the Theory of the Earth, Se. 
on the principles of the theory, subjected to a gradual cooling 
process, it is quite manifest that the contracting influences have 
had their principal seat of action on and near the surface, while 
in the interior their operation has been comparatively feeble. 
We seem therefore to be shut up to the conclusion, that the mo- 
tion of the solid crust about the axis has been more accelerated 
by the cooling and contracting processes than that of the internal 
fused mass—that the angular velocity of the former is more rapid 
than that of the latter—that the latter as a whole is gradually 
falling back of the former. In other words, considering the solid 
crust as fixed relatively to the observer, there is a gradual west- 
erly revolution of the internal fused mass. 
Thus admitting the prevailing theory of the earth, we infer, as 
a necessary physical consequence, a westerly revolution of the 
internal mass; and admitting the western revolution of the in- 
ternal mass, the observed secular motions of the horizontal and 
dipping needles would seem of necessity to follow. 
In looking back on the attempts which have been made to as- 
sign the physical causes of the variation of the declination of the 
needle, it is curious to remark how completely the theory un- 
der consideration embodies the hypothesis of Halley; who 
supposed the earth to have four magnetic poles, two fixed and two 
movable. Regarding the resultant of the magnetic forces of the 
solid crust as indicating the two fixed poles, we have the two 
movable poles of Halley indicated by the resultant of the mag- 
netic forces of the internal fluid mass. The hypothesis of Halley 
may well be set down as an instance of that grasp of mind with 
which “men before their time” seize upon truths, which it may 
require centuries of investigation fully to develop and demon- 
strate. 
It will be observed that in this paper I have confined my re- 
marks to the connexion between the theory of the earth and the 
‘secular motions of the magnetic line. I propose to make the 
bearing of the theory on the subordinate oscillations of the needle 
the subject of a future communication. 
_ Hamilton College, Sept. 1839. 
