cal considerations of some
difficulty, as to which the reader must refer to appropriate books, such
as Balfour Stewart's on _The Conservation of Energy_.

The comprehension of the quantitative aspect of causation is greatly
aided by Bain's analysis of any cause into a 'Moving or an Inciting
Power' and a 'Collocation' of circumstances. When a demagogue by making
a speech stirs up a mob to a riot, the speech is the moving or inciting
power; the mob already in a state of smouldering passion, and a street
convenient to be wrecked, are the collocation. When a small quantity of
strychnine kills a man, the strychnine is the inciting power; the nature
of his nervo-muscular system, apt to be thrown into spasms by that drug,
and all the organs of his body dependent on that system, are the
collocation. Now any one who thinks only of the speech, or the drug, in
these cases, may express astonishment at the disproportion of cause and
effect:

"What great events from trivial causes spring!"

But, remembering that the whole cause of the riot included the excited
mob, every one sees that its muscular power is enough to wreck a street;
and remembering that breathing depends upon the normal action of the
intercostal muscles, it is plain that if this action is stopped by
strychnine, a man must die. Again, a slight rise of temperature may be a
sufficient inciting power to occasion extensive chemical changes in a
collocation of elements otherwise stable; a spark is enough to explode a
powder magazine. Hence, when sufficient energy to account for any effect
cannot be found in the inciting power, or manifestly active condition,
we must look for it in the collocation which is often supposed to be
passive.

And that reminds us of another common misapprehension, namely, that in
Nature some things are passive and others active: the distinction
between 'agent' and 'patient.' This is a merely relative distinction: in
Nature all things are active. To the eye some things seem at rest and
others in motion; but we know that nothing is really at rest, that
everything palpitates with molecular change, and whirls with the planet
through space. Everything that is acted upon reacts according to its own
nature: the quietest-looking object (say, a moss-covered stone), if we
try to push or lift it, pushes or pulls us back, assuring us that
'action and reaction are equal and opposite.' 'Inertia' does not mean
want of vigour, but may be metaphorically des