An introductory text-book of logic - Mellone, Sydney - Rare Books at ...

THE THEORY OF INDUCTION. 265
selective. A man s experience consists, indeed, only
of what he agrees to be interested in. Millions of events
that pass before a man never enter into his experience at
all; they have no interest for him, and hence he does
not notice them. It is a well-founded doctrine of
modern psychology that without selective interest, ex
perience would be an utter chaos.
"
Interest alone gives
accent and emphasis, light and shade, background and
foreground, intelligible perspective,
in a word. Our
own interest lays its weighty index-finger on particular
items of experience, and may emphasise them so as to
give to the least frequent associations far more power to
shape our thoughts than the most frequent ever possess."
And in science the interest springs from previous know
ledge ;
the simplest fact, when noticed by a well-prepared
mind, may become an observation of immense import
ance. The too-familiar anecdotes of James Watt s ob
servation of the force of steam in lifting the kettle-lid,
and Newton s observation of the falling apple, will illus
trate our point. The true observer brings to his observ
ation more than he finds in it, and yet knows how to
abandon one by one his most cherished preconceptions
if the facts will not support them.
We must carefully distinguish between observation
and experiment. In simple observation, the facts
observed are due to Nature ; in experiment, they are
arranged by ourselves. Jevons has excellently described
the difference between the two :
" To
observe is merely to notice events and changes
which are produced in the ordinary course of nature,
without being able, or at least attempting, to control or
vary those changes. Thus the early astronomers ob
served the motions of the sun, moon, and planets among
the fixed stars, and gradually detected many of the laws