& 
64 W. A. Norton on Molecular Physics. 
surface, and to a certain depth below the surface, is the centerof — 
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 © 
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 — 
electric 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 directions 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 center 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 
will be sensibly the sum of the individual actions, and wi 
perpendicular to the line proceeding from the middle of the 
magnet. The directive action of the earth will be virtually this. 
This being allowed, it follows, as deduced in the former paper, 
that, except in high latitudes, the needle will be perpendicular 
to the lines of equal molecular magnetic intensity; also that, the — 
horizontal directive force exerted. by the earth will be propor — 
tional, or nearly so, at each station, to the molecular magnetic 
intensity ; and the vertical force approximatively proportional — 
to the difference of these intensities on one side and the other of © 
the lines of equal force. It may be added here that the above — 
conception brings our theory into essential correspondence ( 
the mechanical point of view) with Gauss’s; and thus that the | 
conclusions of his memoir become deducible from the present — 
ysieal theory. 
__ If we conceive the magnetic force of the earth to be wholly — 
due to the direct action of the electric currents, circulating from 
molecule to molecule, the force exerted by each element of the — 
current should be of the same character, and havea similar direc- 
tion to that in the case just supposed. But, since the resultant — 
currents are shifting their position from year to year, it follows 
oat they may differ somewhat from the lines of equal molecular 
