tion of life, or rather during the evolution of that series of
organisms through which the human organism has been reached. The
effects of the most uniform and frequent of these experiences have
been successively bequeathed, principal and interest, and have slowly
mounted to that high intelligence which lies latent in the brain of
the infant. Thus it happens that the European inherits from twenty to
thirty cubic inches more of brain than the Papuan. Thus it happens
that faculties, as of music, which scarcely exist in some inferior
races, become congenital in superior ones. Thus it happens that out
of savages unable to count up to the number of their fingers, and
speaking a language containing only nouns and verbs, arise at length
our Newtons and Shakspeares.'

8.

At the outset of this Address it was stated that physical theories
which lie beyond experience are derived by a process of abstraction
from experience. It is instructive to note from this point of view
the successive introduction of new conceptions. The idea of the
attraction of gravitation was preceded by the observation of the
attraction of iron by a magnet, and of light bodies by rubbed amber.
The polarity of magnetism and electricity also appealed to the senses.
It thus became the substratum of the conception that atoms and
molecules are endowed with attractive and repellent poles, by the play
of which definite forms of crystalline architecture are produced. Thus
molecular force becomes structural. [Footnote: See Art. on Matter and
Force, or 'Lectures on Light,' No. III.] It required no great
boldness of thought to extend its play into organic nature, and to
recognise in molecular force the agency by which both plants and
animals are built up. In this way, out of experience arise
conceptions which are wholly ultra-experiential. None of the atomists
of antiquity had any notion of this play of molecular polar force, but
they had experience of gravity, as manifested by falling bodies.
Abstracting from this, they permitted their atoms to fall eternally
through empty space. Democritus assumed that the larger atoms moved
more rapidly than the smaller ones, which they therefore could
overtake, and with which they could combine. Epicurus, holding that
empty space could offer no resistance to motion, ascribed to all the
atoms the same velocity; but he seems to have overlooked the
consequence that under such circumstances the atoms could never
combine.