is met with as
heredity, experience, tradition. Evolution of species of plants and
animals would (so far as we know) be impossible, if the changes (however
caused) that adapt some individuals better than others to the conditions
of life were not inherited by, and accumulated in, their posterity. The
eyes in the peacock's tail are supposed to have reached their present
perfection gradually, through various stages that may be illustrated by
the ocelli in the wings of the Argus pheasant and other genera of
_Phasianidae_. Similarly the progress of societies would be impossible
without tradition, whereby the improvements made in any generation may
be passed on to the next, and the experience of mankind may be gradually
accumulated in various forms of culture. The earliest remains of culture
are flint implements and weapons; in which we can trace the effect of
tradition in the lives of our remote forefathers, as they slowly through
thousands of years learnt to improve the chipping of flints, until the
first rudely shaped lumps gave place to works of unmistakable design,
and these to the beautiful weapons contemporary with the Bronze Age.

The Method of Gradations, the arranging of any phenomena to be studied
in series, according to the degree in which some character is exhibited,
is, perhaps, the most definite device in the Art of Discovery. (Bain:
_Induction_, c. 6, and App. II.) If the causes are unknown it is likely
to suggest hypotheses: and if the causes are partly known, variation in
the character of the series is likely to indicate a corresponding
variation of the conditions.

Sec. 5. THE CANON OF RESIDUES.

_Subduct from any phenomenon such part as previous inductions have shown
to be the effect of certain antecedents, and the residue of the
phenomenon is the effect of the remaining antecedents_.

The phenomenon is here assumed to be an effect: a similar Canon may be
framed for residuary causes.

This also is not a fresh method, but a special case of the method of
Difference. For if we suppose the phenomenon to be _p q r_, and the
antecedent to be A B C, and that we already know B and C to have (either
severally or together) the consequents _q r_, in which their efficacy is
exhausted; we may regard

B C
_q r_

as an instance of the absence of _p_ obtained deductively from the whole
phenomenon

A B C
_p q r_

by our knowledge of the laws of B and C; so that

A B C
_p q r_

is an instance of the p