MAGNETIC CONDUCTION. 
31 
qualities by the term conduction-, but in the present state of the subject, and under 
the reservation already made (2797.), the phrase may I think be employed conve- 
niently without introducing' confusion. 
2803. If such be a correct general view of the nature and differences of paramag- 
netic and diamagnetic substances, then the internal processes by which they perform 
their functions can hardly be the same, though they might be similar. Thus they 
may have circular electric currents in opposite directions, but their distinction can 
scarcely be supposed to depend upon the difference of force of currents in the same 
direction. If the view be correct also, though the results obtained when two 
bodies are simultaneously present in the magnetic field may be considered as differ- 
ential (2770. 2768.) even though one of them be the general medium, yet the con- 
sequence of the presence of conducting power in matter renders a single body, when 
in space, subject to the magnetic force ; and the result is, that when a paramagnetic 
substance is in a magnetic field of unequal force, it tends to proceed from weaker to 
stronger places of action, or is attracted; and when a diamagnetic body is similarly 
circumstanced, it tends to go from stronger to weaker places of action, or is repelled 
(2756.). 
2804. Matter, when its powers are under consideration, may, as to its quantity, be 
considered either by weight or by volume. In the present case, where the effects 
produced have an immediate reference to mere space (2787- 2802.), it seems proper 
that the volume should be considered as the representation, and that in comparing 
one substance with another, equal volumes should be employed to give correct 
results. No other method could be used with the differential system of observation 
(2772. 2780.). 
2805. Some experimental evidence, other than those of change of situation, of the 
existence of this conducting power, by differences in which, I am endeavouring to 
account for the peculiar characteristics of paramagnetic and diamagnetic bodies, may 
well be expected. This evidence exists ; but as certain considerations connected with 
polarity preclude me from calling too freely upon iron, cobalt, or nickel (2832.) for 
illustrations, and as in other bodies which are paramagnetic, as well as in those that 
are diamagnetic, the effects are very weak, they will be better comprehended after 
some further general consideration of the subject (2843.). 
2806. I will now endeavour to consider what the influence is which paramagnetic 
and diamagnetic bodies, viewed as conductors (2797-), exert upon the lines of force 
in a magnetic field. Any portion of space traversed by lines of magnetic power, may 
be taken as such a field, and there is probably no space without them. The condi- 
tion of the field may vary in intensity of power, from place to place, either along the 
lines or aeross them ; but it will be better to assume for the present consideration a 
field of equal force throughout, and I have formerly described how this may, for a 
