object by
other sciences. Did we proceed upon the abstract theory of forces, we
should assign a much more ample range to a projectile than in fact the
resistance of the air allows it to accomplish. Let, however, that
resistance be made the subject of scientific analysis, and then we shall
have a new science, assisting, and to a certain point completing, for the
benefit of questions of fact, the science of projection. On the other
hand, the science of projection itself, considered as belonging to the
forces it contemplates, is not more perfect, as such, by this
supplementary investigation. And in like manner, as regards the whole
circle of sciences, one corrects another for purposes of fact, and one
without the other cannot dogmatize, except hypothetically and upon its own
abstract principles. For instance, the Newtonian philosophy requires the
admission of certain metaphysical postulates, if it is to be more than a
theory or an hypothesis; as, for instance, that what happened yesterday
will happen to-morrow; that there is such a thing as matter, that our
senses are trustworthy, that there is a logic of induction, and so on. Now
to Newton metaphysicians grant all that he asks; but, if so be, they may
not prove equally accommodating to another who asks something else, and
then all his most logical conclusions in the science of physics would
remain hopelessly on the stocks, though finished, and never could be
launched into the sphere of fact.

Again, did I know nothing about the movement of bodies, except what the
theory of gravitation supplies, were I simply absorbed in that theory so
as to make it measure all motion on earth and in the sky, I should indeed
come to many right conclusions, I should hit off many important facts,
ascertain many existing relations, and correct many popular errors: I
should scout and ridicule with great success the old notion, that light
bodies flew up and heavy bodies fell down; but I should go on with equal
confidence to deny the phenomenon of capillary attraction. Here I should
be wrong, but only because I carried out my science irrespectively of
other sciences. In like manner, did I simply give myself to the
investigation of the external action of body upon body, I might scoff at
the very idea of chemical affinities and combinations, and reject it as
simply unintelligible. Were I a mere chemist, I should deny the influence
of mind upon bodily health; and so on, as regards the devotees of a