Prof- Norton on Molecular Phijsics. 267 



in originating and maintaining the normal magnetism of the 

 earth, and determining the secular changes that occur in its dis- 

 tribution. The currents resulting from the earth's rotation can 

 serve only to maintain a uniform normal condition of such cur- 

 rents previously developed. But the aether of space also impinges 

 normally upon the forward side of the earth. The principal effect 

 of this mode of action, that we have occasion to consider, will be 

 the origination of a series of waves of translation in the sea of 

 electric aether that pervades the interstices of the molecules, 

 spreading out from the most advanced point of the earth. They 

 may be conceived to consist of an endless number of linear cur- 

 rents radiating in great circles from that point. This description 

 of currents exhibit their effects conspicuously in the daily and 

 annual variations of the declination and directive force of the 

 needle. They conspire with the others, and to a certain extent 

 modify them, and originate similar ones. 



It should be added that the more permanent magnetic forces 

 developed by the currents above considered may consist, in a 

 great degree, in secondary currents excited within the molecules 

 of the earth. The author's former investigations accord with 

 this view. In a memoir " On Terrestrial Magnetism/' published 

 hi Silliman's Journal, vol. iv. p. 1, a theory of the magnetic action 

 of the earth was propounded and discussed, based upon the fun- 

 damental assumption that " every particle of matter at the earth's 

 surface, and to a certain depth below the surface, is the centre 

 of a magnetic force exerted tangentially to the circumference of 

 every vertical circle that may be conceived to be traced around 

 it." This tangential action upon the north pole of the needle 

 was conceived to be directed downward on the north side of 

 the particle, and upward on the south side (see p. 4 of the 

 paper just referred to). Now, if we regard the particles of the 

 earth's crust as so many separate magnets — magnetized by elec- 

 tric currents developed as we have been considering — we are 

 conducted by an inevitable sequence to this fundamental basis 

 of the theory in question ; for all such molecular magnets will 

 at each station have their axes perpendicular to the resultant 

 currents traversing that station to which the magnetization is 

 due. The north end of every such indefinitely small magnet 

 will exert an attractive force upon the north end of the needle, 

 and the south end will exert an equal repulsive force upon the 

 north end of the needle. Since the lines of direction of these 

 forces will not be strictly coincident, their resultant will bisect 

 the outer angle between them, and so be perpendicular to the 

 line proceeding from the centre of the molecular magnet. A 

 series of such minute magnets extending for a small distance 

 will form a magnet of finite length, the entire action of which 



