96 Prof, Challis on a Theory of Magnetic Force. 
hydrodynamical considerations, that converging and diverging 
streams impress upon them the same moving forces, if the velo- 
cities be the same, and the degree of convergency be equal to 
that of divergency; but the forces will be in opposite direc- 
tions with respect to the course of the streams. Hence, under 
those circumstances, if one magnetic pole be attractive, the 
other will be attractive also, and in the same degree. This 
result experience confirms. 
21. If a bar of bismuth be suspended either horizontally or 
vertically between the poles of a magnet, it is found to be im- 
pelled in the directions of the lines of motion from the poles. 
The action is therefore opposed to that which results from va- 
riation of density of the ether. The same effect took place when 
the bismuth was broken into very small pieces. Also it appeared 
that two pieces of bismuth subject to the action of magnetic 
streams, exerted no influence on each other; that is, no se- 
condary streams were generated. From these facts it must be 
concluded theoretically, that convergent and divergent magnetic 
streams, when they enter bismuth and substances of the same 
class, and are modified by the number, size, and arrangement 
of the constituent atoms, impress on the individual atoms acce- 
lerative forces, which impel them along the lines of motion from 
the magnetic poles. For the same reason as that above given 
in the case of iron, the action is alike from both poles, and in 
the same degree, although the streams diverge from one and 
converge towards the other. 
22. It is found by experiment that aw and gases are not 
sensibly acted upon by magnetic streams. This fact may be 
explained by the theory on the supposition that such substances, 
on account of their small density, do not perceptibly, by the 
state of aggregation of their atoms, modify the etherial streams, 
which consequently act on each atom as if it were alone. Now 
in that case a divergent stream impels the atom in the direction 
of the course, and a convergent stream draws it in the direction 
contrary to the course, and it is possible that these actions may 
be just counteracted by the opposite effects of the variation of 
density of the ether. 
23. Since the magnetic streams attract one class of substances 
(the magnetic) towards the poles, and repel another class (the 
diamagnetic) from the poles, we might expect to meet with 
other substances which are neither attracted nor repelled, or are 
only acted upon very fecbly. This appears to be the case with 
copper. ‘The peculiar phenomena (Faraday, 2309, &c.) which 
this metal exhibits when placed between the poles of a magnet, 
seem to admit of explanation on the principles of this theory, 
by supposing its atoms to be easily moveable from their normal 
—_— ~ — 
ee a 
Se Se ee eee 
_—* a ee a 
