A System of Logic: Ratiocinative and Inductive, 7th Edition, Vol. II
John Stuart Mill · en
but it actually happens, in almost all cases in which the obtaining of
the right conception is a matter of any considerable difficulty. For if
there be no new conception required; if one of those already familiar to
mankind will serve the purpose, the accident of being the first to whom
the right one occurs, may happen to almost anybody; at least in the case
of a set of phenomena which the whole scientific world are engaged in
attempting to connect. The honour, in Kepler's case, was that of the
accurate, patient, and toilsome calculations by which he compared the
results that followed from his different guesses, with the observations
of Tycho Brahe; but the merit was very small of guessing an ellipse; the
only wonder is that men had not guessed it before, nor could they have
failed to do so if there had not existed an obstinate _à priori_
prejudice that the heavenly bodies must move, if not in a circle, in
some combination of circles.
The really difficult cases are those in which the conception destined to
create light and order out of darkness and confusion, has to be sought
for among the very phenomena which it afterwards serves to arrange. Why,
according to Dr. Whewell himself, did the ancients fail in discovering
the laws of mechanics, that is, of equilibrium and of the communication
of motion? Because they had not, or at least had not clearly, the ideas
or conceptions of pressure and resistance, momentum, and uniform and
accelerating force. And whence could they have obtained these ideas,
except from the very facts of equilibrium and motion? The tardy
development of several of the physical sciences, for example of optics,
electricity, magnetism, and the higher generalizations of chemistry, he
ascribes to the fact that mankind had not yet possessed themselves of
the Idea of Polarity, that is, the idea of opposite properties in
opposite directions. But what was there to suggest such an idea, until,
by a separate examination of several of these different branches of
knowledge, it was shown that the facts of each of them did present, in
some instances at least, the curious phenomenon of opposite properties
in opposite directions? The thing was superficially manifest only in two
cases, those of the magnet, and of electrified bodies; and there the
conception was encumbered with the circumstance of material poles, or
fixed points in the body itself, in which points this opposition of
properties seemed to be inherent. The first comparison and abstraction
had led only to this conception of poles; and if anything corresponding
to that conception had existed in the phenomena of chemistry or optics,
the difficulty now justly considered so great, would have been extremely
small. The obscurity rose from the fact, that the polarities in
chemistry and optics were distinct species, though of the same genus,
with the polarities in electricity and magnetism: and that in order to
assimilate the phenomena to one another, it was necessary to compare a