electricity and magnetism.
The whole scheme of these important sciences rests on the hypothesis
of "electric fluidity," or of imponderable matter of which the
existence is nothing less than proved. Or optics? Optics certainly
appertain to the most important and completest branch of physics, and
yet the undulatory theory of light, which we accept now as the
indispensable basis of optics, rests on an unproved hypothesis, on the
subjective assumption of an ethereal medium, whose existence no one is
in a position to prove objectively in any way. Nay, further, before
Young set up the undulatory theory of light, for a hundred years the
emanation theory as taught by Newton obtained exclusively in physics;
a theory which at the present day is universally regarded as
untenable. In our opinion the mighty Newton won the greatest honours
in the development of the science of optics, inasmuch as he was the
first to connect and explain the vast mass of objective optical facts
by a subjective and pregnant hypothesis. But, according to Virchow's
view, Newton on the contrary transgressed greatly by teaching this
erroneous hypothesis; for even in "exact" physics none but
"independent and certain facts" are to be taught and established by
"experiment as the highest means of proof." Physics as a whole, as
resting on mere unproved hypotheses, may be indeed an object of
inquiry but not of teaching.

Of course the same is true of chemistry; nay, this stands on much
weaker feet, and is even less proved than physics. The whole
theoretical side of chemistry is an airy structure of hypotheses such
as does not exist in any other science. In the last three decades we
have seen a whole series of the most different theories rapidly
succeed each other, none of which can be positively proved, though at
least one of them is taught by every professor of chemistry. But what
is worst of all, the common basis of all the most dissimilar chemical
theories, viz., the atomic theory, is as unproved and unprovable as
any hypothesis can be. No chemist has ever seen an atom, but he
nevertheless considers the mechanism of atoms as the highest term of
his science, he nevertheless describes and constructs the connection
of atoms in their various combinations as though he had them before
him on the dissecting-table! All the conceptions which we possess as
to chemical structure and the affinities of matter, are subjective
hypotheses, mere conceptions as to the position