P. E. Chase on Terrestrial Magnetism. 373 
Art. XXXVII.—Dependence of Terrestrial Magnetism on Atmos- 
_ pheric Currents; by Puiny Earte Case, M.A., 8.P.A.S.* 
ON account of the mutual dependence of all the forces of na- 
ture, and the reasonableness of Prof. Faraday’s conjecture, that 
they are often, if not always, convertible more or less into each 
other,’ it seems probable that the disturbances of the magnetic 
needle may be as closely connected with the earth’s rotation, 
and the continually changing position of each point relatively 
to the sun, as those of the barometer and thermometer. Ampére 
held that the earth is an electro-magnet, magnetized by an elec- 
tric current from east to west, the current being excited by the 
action of the sun’s heat successively on different parts of the 
earth’s surface as it revolves toward the east. The friction of 
De Lue, and by Gen, Sabine’s observation, that when the sun 
and moon were on the meridian, the magnetic variation reached 
5°, but when they were in quadrature, it fell as low as 2 fa 
_ The great forces of nature can be measured only by their dis- 
turbances or their deviations from uniformity. The action of 
gravity is so nearly uniform at all times and in all parts of the 
globe, that it is difficult to imagine any crucial experiment that 
Could demonstrate its relations to magnetism. Perhaps a needle, 
€xperiments were tried, to show the relative influence of gravity 
Upon each extremity, both before and after magnetizing, and 
when subjected to artificial magnetism, so as to produce various 
amounts of deviation from the normal dip and declination. Or, 
centrifugal force, so applied as alternately to assist and oppose 
the effects of gravity, as in large fly-wheels revolving with va- 
* From the Proceedings of the Am. Phil. Soc. 
_, Phil. Mag,, [4], 5 6 % 
See correspon of M. J. Nicklés, this Journal, [2], xvii, 117, &c. 
_ * This Journal, [2], xix, 424. | 
