48 Mr. J.S. Stuart Glennie on the 
thus a magnet is conceived as a body the molecular centres of 
pressure of which are transversely displaced about an axis 
joining its poles. 
19. As has been said, the fitness of conceptions of the nature 
and states of electricity is to be proved chiefly by their explana- 
tions of the effects of electricity; but note also, in support of 
these conceptions of current electricity, such facts, as to the 
origin of open currents, as that mere difference in the motions of 
metals in contact develope in them electric currents ; and, as to 
closed currents, note that the experimental conditions which de- 
fine a closed current, and the facts as to the molecular structure 
of magnets, however much they may still require investigation, 
seem already to justify a conception of magnetism wholly re- 
ferable to conditions of mechanical action and resistance—a 
conception the antithesis of that which “associates”? with bodies 
‘latent virtues’ and “neutral fluids,”’ and a conception which 
evidently differs also, though with respect, from the later 
theories in which mechanical principles are applied, not imme- 
diately to phenomena, but to, as it should seem, needless hypo- 
theses of “ zthers*.” 
20. (III). The effects of electricity may be generalized under 
these heads :—(A) induction; (a) msulation; (() discharge ; 
the latter distinguishable into (1) conduction ; (2) eleetrolytic 
discharge ; (3) disruptive discharge ; (4) convection, or carrying 
discharget: (B) motion (@ of bodies; conveniently classed as 
(1) ordinary attractions and repulsions; (2) paramagnetism 
and diamagnetism; (3) right- or left-handed deviations or ro- 
tations ; (8) motion of the medium, including heat and light, 
&c. vibrations. 
21. (A) Induction is conceived as the necessary mechanical 
consequence in a plenum of the displacement of centres of lines 
of pressure. For it is clear that, if the parts of matter are con- 
ceived as mutually repelling, and such repulsion is mechanically 
conceived in such forms as those above suggested—as the elas- 
ticity of atomic centres, or as lines of pressure from molecules, 
—the displacement of the molecules forming a line of centres 
of pressure implies a disturbance of the previously existing me- 
chanical relations, not only at the extremities of, but ail round 
such a line of displacement; and such a conception implies, 
further, that the character of such disturbance depends entirely on 
the relations between the direction and intensity of the original 
* T would desire more especially to express the diffidence and respect 
with which I venture to differ from Professor Challis as to the necessity 
or advantage of the fundamental hypothesis of his theory. See Phil. Mag. 
February, October, and December 1860. 
ft Faraday, ‘ Experimental Researches,’ Series VII. 1319. 
