Chase.] 374 [February. 



of a definable connection between gravity and magnetism, a 

 connection which had long been suspected, which was rendered 

 increasingly probable by the resemblance of the lunar declina- 

 tion-curve to the regular tidal-curve, and which was verified b} 

 my numerical computations (Trans. A. P. S., vol. xiii, pp. 117- 

 136) ; the increase of lunar force at syzygy and at full moon 

 may be easily understood if we are satisfied to refer it to tidal- 

 attraction ; \inder the diminished pressure at low barometer 

 there is less resistance to any disturbance of fluid motion ; 

 Arago, Ampere, Barlow, and Christie, showed that the simple 

 rotation of bodies, constituted of any material whatever, gener- 

 ates magnetic currents ; the use of percussion and vibration 

 in magnetizing or demagnetizing iron bars, Leverrier's daily 

 meteorological reports, Palmieri's observations during the re- 

 cent eruptions of Vesuvius, and my experiments with merely 

 mechanical vibrations and currents analogous to those which 

 are constantlj^ agitating the atmosphere {ante^ v. ix, p. 359 ; x, 

 151, &c.), furnish abundant evidence of the effects of local agi- 

 tation. 



Much of the later theorizing and investigation has proceeded 

 on Ampere's assumption, that the earth is an electro-magnet, 

 magnetized by an electric current which flows from east to 

 west, the current being excited by the action of the sun's heat 

 successively in different parts of the earth's surface, as it re- 

 volves toward the east, but little has been done towards remov- 

 ing the difficulties which are supposed to surround that h}-- 

 pothesis. There is, perhaps, an increasing tendency' to regard 

 the sun as a true magnet, exciting the earth solely by its in- 

 duction. But such a theory serves merely as a cloak for our 

 ignorance. Even if the sun and earth were each solid masses 

 of magnetized iron, the solar inductive action on the earth 

 would be relatively no greater than that of a globular magnet, 

 one foot in diameter, upon an iron shot, one-ninth of an inch 

 in diameter, at a distance of one hundred and ten feet.* 



Electricity and magnetism are both manifested as forces 

 which tend to a speedy equilibrium. Whether the equilibrium 

 is disturbed by friction, by mechanical separation, by chemical 



* See Dr. Lloyd's demonstration that " the phenomena of the diurnal 

 variation are not caused by the direct ^nagnetic action of the sun and 

 moon." (Phil. Mag. [4] xv, 192-6.) 



