sition and the relation alleged between them; and there must be
such definite and deliberate mental representation of these terms as
makes possible a clear consciousness of this relation.... Along with
acquirement of more complex faculty and more vivid imagination, there
comes a power of perceiving to be necessary truths, what were before not
recognized as truths at all.... All this which holds of logical and
mathematical truths, holds, with change of terms, of physical truths.
There are necessary truths in Physics for the apprehension of which,
also, a developed and disciplined intelligence is required; and before
such intelligence arises, not only may there be failure to apprehend the
necessity of them, but there may be vague beliefs in their
contraries.... But though many are incapable of grasping physical
axioms, it no more follows that physical axioms are not knowable _a
priori_ by a developed intelligence, than it follows that logical
relations are not necessary, because undeveloped intellects cannot
perceive their necessity.

"The terms '_a priori_ truth' and 'necessary truth' ... are to be
interpreted," he continues, "not in the old sense, as implying
cognitions wholly independent of experiences, but as implying cognitions
that have been rendered organic by immense accumulations of experiences,
received partly by the individual, but mainly by all ancestral
individuals whose nervous systems he inherits. But when during mental
evolution, the vague ideas arising in a nervous structure imperfectly
organized, are replaced by clear ideas arising in a definite nervous
structure; this definite structure, molded by experience into
correspondence with external phenomena, makes necessary in thought the
relations answering to absolute uniformities in things. Hence, among
others, the conception of the Indestructibility of Matter.... Our
inability to conceive Matter becoming non-existent, is immediately
consequent upon the nature of thought.... It must be added, that no
experimental verification of the truth that Matter is indestructible, is
possible without a tacit assumption of it. For all such verification
implies weighing, and weighing implies that the matter forming the
weight remains the same. In other words, the proof that certain matter
dealt with in certain ways is unchanged in quantity, depends on the
assumption that other matter otherwise dealt with is unchanged in
quantity."

In answer to the above it can be sai