Chase.] 355 [April. 



On account of the mutual dependence of all the forces of nature, 

 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. Ampere held that the earth is an 

 electro-magnet, magnetized by an electric 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 trade-winds and ocean-currents and the varia- 

 tions of light and temperature that are produced by rotation and orbital 

 revolution, must exert an influence upon the magnetic needle, and 

 beside these indirect eff'ects, M. Arago showed that simple rotation, 

 in some unknown way, produces magnetism in bodies of every de- 

 scription. Many have supposed that this magnetism is derived from 

 the earth by induction, but on account of the impossibility of escap- 

 ing from the influence of terrestrial magnetism, it is difiicult to obtain 

 any conclusive evidence on the subject. f A similar impossibility 

 has interfered with Prof. Faraday's endeavors to connect gravity and 

 magnetic or electric action by experimental results. The probability 

 of such a connection has been shown by the electricity developed in 

 the dry pile of De Luc, 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 20'.| 



The great forces of nature can be measured only by their disturb- 

 ances 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 

 difl&cult to imagine any crucial experiment that could demonstrate 

 its relations to magnetism. Perhaps a needle, hinged at its point of 

 support, with the two extremities nicely balanced, might help us 

 towards such a demonstration, if careful experiments were tried, to 

 show the relative influence of gravity upon each extremity, both be- 

 fore and after magnetizing, and when subjected to artificial magnet- 

 ism, 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 eff'ects of gravity, as in large fly-wheels re- 

 volving with various degrees of rapidity, may indicate variations of 



* Phil. Mag. 4th Ser. 1, 68. 



t See correspondence of M. J. Nickles, Silliman's Journal, v. 17, p. 117, &c. 



J Silliman's Journal, vol. 19, p. 424. 



