aporation. It is no doubt true, as M. Comte says,
that "our position in the solar system, and the motions, form, size,
equilibrium of the mass of our world among the planets, must be known
before we can understand the phenomena going on at its surface." But,
fatally for his hypothesis, it is also true that we must understand a
great part of the phenomena going on at its surface before we can know
its position, etc., in the solar system. It is not simply that, as we
have already shown, those geometrical and mechanical principles by which
celestial appearances are explained, were first generalised from
terrestrial experiences; but it is that the very obtainment of correct
data, on which to base astronomical generalisations, implies advanced
terrestrial physics.

Until after optics had made considerable advance, the Copernican system
remained but a speculation. A single modern observation on a star has to
undergo a careful analysis by the combined aid of various sciences--has
to _be digested by the organism of the sciences_; which have severally
to assimilate their respective parts of the observation, before the
essential fact it contains is available for the further development of
astronomy. It has to be corrected not only for nutation of the earth's
axis and for precession of the equinoxes, but for aberration and for
refraction; and the formation of the tables by which refraction is
calculated, presupposes knowledge of the law of decreasing density in
the upper atmospheric strata; of the law of decreasing temperature, and
the influence of this on the density; and of hygrometric laws as also
affecting density. So that, to get materials for further advance,
astronomy requires not only the indirect aid of the sciences which have
presided over the making of its improved instruments, but the direct aid
of an advanced optics, of barology, of thermology, of hygrometry; and if
we remember that these delicate observations are in some cases
registered electrically, and that they are further corrected for the
"personal equation"--the time elapsing between seeing and registering,
which varies with different observers--we may even add electricity and
psychology. If, then, so apparently simple a thing as ascertaining the
position of a star is complicated with so many phenomena, it is clear
that this notion of the independence of the sciences, or certain of
them, will not hold.

Whether objectively independent or not, they cannot be s