1864.] 491 [Chase. 



The mutual convertibility of Light, Heat, Electricity, Magnetism, 

 Chemical Affinity, and Vital Energy, may be now regarded as one 

 of the most probable physical hypotheses. Faraday has endeavored 

 also to connect gravitation and magnetism or electric action by expe- 

 rimental results, but in vain. Still, the conviction of such a con- 

 nection is almost irresistible, and various physicists have given us 

 incidental pointings in that direction. Ampere discovered the mag- 

 netic effect of electric currents circulating around iron bars ; Arago, 

 vrbose experiments were repeated and extended by Babbage, Her- 

 schel, Barlow, Christie, and others, showed that simple rotation pro- 

 duces magnetic disturbances which are governed by fixed laws ; the 

 distribution of induced magnetism in masses of iron, as determined 

 by Barlow and Lecount, is the same as would follow from the relative 

 centrifugal motions of different portions of the earth, provided the 

 magnetic axis corresponded with the axis of rotation ■* Hansteen sus- 

 pected, and Sabine practically demonstrated, the influence of the sun 

 upon terrestrial magnetism; Secchi ascertained that "the diurnal 

 excursion of the needle is the sum of two distinct excursions, of 

 which the first depends solely on the horary angle, and the second 

 depends, besides, on the sun's declination, "f and that " all the phe- 

 nomena hitherto known of the diurnal magnetic variations may be 

 explained by supposing that the sun acts upon the earth as a very 

 powerful magnet at a great distance. "[{; 



This hypothesis has been objected to on the ground that it is diffi- 

 cult to understand how any conceivable intensity of solar magnetism, 

 by its simple induction, could produce so great a disturbance as is 

 daily observed. Therefore it will probably follow the fate of the 

 earlier ones, which attributed terrestrial magnetism to one or more 

 powerful magnets lying nearly in the line of the earth's axis, while 

 Barlow's idea that the magnetism is superficial and in some manner 

 induced,! will still remain in the ascendant. Secchi's conclusions are, 

 however, none the less interesting, and from the fact that magnetism 

 is, like gravity, a central force, varying inversely as the square of the 

 distance, they lend encouragement to those who are endeavoring to 

 find new evidences of the unity of force. 



My own experiments and researches have led me to the belief that 

 all magnetism is a simple reaction against a force which disturbs 



* This fact was first announced by me, at the Society's meeting, April 15, 

 1864. See ante, p. 367. 



t Phil. Mag. [4] 8, .396. f Ibid. 9, 452. ^ Phil. Trans., 1831. 



