to sample. If it is brought before a
thinker for a moment that in any special case this is not so, he slips
back to the old attitude as soon as his attention is withdrawn. This
source of error has, for instance, caught nearly the whole race of
chemists, with one or two distinguished exceptions, and _atoms_ and
_ions_ and so forth of the same species are tacitly assumed to be
similar one to another. Be it noted that, so far as the practical
results of chemistry and physics go, it scarcely matters which
assumption we adopt. For purposes of inquiry and discussion the
incorrect one is infinitely more convenient.

But this ceases to be true directly we emerge from the region of
chemistry and physics. In the biological sciences of the eighteenth
century, commonsense struggled hard to ignore individuality in shells
and plants and animals. There was an attempt to eliminate the more
conspicuous departures as abnormalities, as sports, nature's weak
moments, and it was only with the establishment of Darwin's great
generalisation that the hard and fast classificatory system broke down,
and individuality came to its own. Yet there had always been a clearly
felt difference between the conclusions of the biological sciences and
those dealing with lifeless substance, in the relative vagueness, the
insubordinate looseness and inaccuracy of the former. The naturalist
accumulated facts and multiplied names, but he did not go triumphantly
from generalisation to generalisation after the fashion of the chemist
or physicist. It is easy to see, therefore, how it came about that the
inorganic sciences were regarded as the true scientific bed-rock. It
was scarcely suspected that the biological sciences might perhaps, after
all, be _truer_ than the experimental, in spite of the difference in
practical value in favour of the latter. It was, and is by the great
majority of people to this day, supposed to be the latter that are
invincibly true; and the former are regarded as a more complex set of
problems merely, with obliquities and refractions that presently will be
explained away. Comte and Herbert Spencer certainly seem to me to have
taken that much for granted. Herbert Spencer no doubt talked of the
unknown and the unknowable, but not in this sense, as an element of
inexactness running through all things. He thought of the unknown as the
indefinable beyond to an immediate world that might be quite clearly and
exactly known.

Well, there is a