g
with the tidal movements of the ocean, takes no account of the waves
made by the wind, or by the pressure of all the steamers which day and
night are moving their thousands of tons upon its surface. Just so the
marksman, in sighting his rifle, allows for the motion of the wind, but
not for the equally real motion of the earth and solar system. Just so
a business man's punctuality may overlook an error of five minutes,
while a physicist, measuring the velocity of light, must count each
thousandth of a second.

There are, in short, _different cycles of operation_ in nature;
different departments, so to speak, relatively independent of one
another, so that what goes on at any moment in one may be compatible
with almost any condition of things at the same time in the next. The
mould on the biscuit in the store-room of a {221} man-of-war vegetates
in absolute indifference to the nationality of the flag, the direction
of the voyage, the weather, and the human dramas that may go on on
board; and a mycologist may study it in complete abstraction from all
these larger details. Only by so studying it, in fact, is there any
chance of the mental concentration by which alone he may hope to learn
something of its nature. On the other hand, the captain who in
manoeuvring the vessel through a naval fight should think it necessary
to bring the mouldy biscuit into his calculations would very likely
lose the battle by reason of the excessive 'thoroughness' of his mind.

The causes which operate in these incommensurable cycles are connected
with one another only _if we take the whole universe into account_.
For all lesser points of view it is lawful--nay, more, it is for human
wisdom necessary--to regard them as disconnected and irrelevant to one
another.

And this brings us nearer to our special topic. If we look at an
animal or a human being, distinguished from the rest of his kind by the
possession of some extraordinary peculiarity, good or bad, we shall be
able to discriminate between the causes which originally _produced_ the
peculiarity in him and the causes that _maintain_ it after it is
produced; and we shall see, if the peculiarity be one that he was born
with, that these two sets of causes belong to two such irrelevant
cycles. It was the triumphant originality of Darwin to see this, and
to act accordingly. Separating the causes of production under the
title of 'tendencies to spontaneous variation,' and relegating t