he elements), have been often found, especially in the
case of vital and mental phenomena, to enter _unaltered_ into
composition with one another, so that complex facts may thus be
_deducible_ from comparatively simple laws. It is even possible that, as
has been already partly effected by Dalton's law of definite
proportions, and the law of isomorphism, chemistry itself, which is now
the least deductive of sciences, may be made deductive, through the laws
of the combinations being ascertained to be, though not compounded of
the laws of the separate agencies, yet derived from them according to a
fixed principle.

The proposition, that effects are proportional to their causes, is
sometimes laid down as an independent axiom of causation: it is really
only a particular case of the composition of causes; and it fails at the
same point as the latter principle, viz. when an addition does not
become compounded with the original cause, but the two together generate
a new phenomenon.

CHAPTER VII.

OBSERVATION AND EXPERIMENT.

Since the whole of the present facts are the infallible result of the
whole of the past, so that if the prior state of the entire universe
could recur it would be followed by the present, the process of
ascertaining the relations of cause and effect is an analysis or
resolution of this complex uniformity into the simpler uniformities
which make it up. We must first mentally analyse the facts, not making
this analysis minuter than is needed for our object at the time, but at
the same time not regarding (as did the Greeks their verbal
classifications) a mental decomposition of facts as ultimate. When we
have thus succeeded in looking at any two successive chaotic masses (for
such nature keeps at each instant presenting to us) as so many distinct
antecedents and consequents, we must analyse the facts themselves, and
try, by varying the circumstances, to discover which of the antecedents
and consequents (for many are always present together) are related to
each other.

Experiment and observation are the two instruments for thus varying the
circumstances. When the enquiry is, What are the effects of a given
cause? experiment is far the superior, since it enables us not merely to
produce many more and more opportune variations than nature, which is
not arranged on the plan of facilitating our studies, offers
spontaneously, but, what is a greater advantage, though one less
attended to, also to insul