y theory of light called for the
extension of the same theory to heat, electricity, and magnetism, and
this promptly suggested the hypothesis of a correlation, material
connection, and transmutability of heat, light, electricity,
magnetism, etc.; which hypothesis the physicists held in absolute
suspense until very lately, but are now generally adopting. If not
already established as a system, it promises soon to become so. At
least, it is generally received as a tenable and probably true
hypothesis.

Parallel to this, however less cogent the reasons, Darwin and others,
having shown it likely that some varieties of plants or animals have
diverged in time into cognate species, or into forms as different as
species, are led to infer that all species of a genus may have thus
diverged from a common stock, and thence to suppose a higher community
of origin in ages still farther back, and so on. Following the safe
example of the physicists, and acknowledging the fact of the
diversification of a once homogeneous species into varieties, we may
receive the theory of the evolution of these into species, even while
for the present we hold the hypothesis of a further evolution in cool
suspense or in grave suspicion. In respect to very many questions a
wise man's mind rests long in a state neither of belief nor of
unbelief. But your intellectually short-sighted people are apt to be
preternaturally clear-sighted, and to find their way very plain to
positive conclusions upon one side or the other of every mooted
question.

In fact, most people, and some philosophers, refuse to hold questions
in abeyance, however incompetent they may be to decide them. And,
curiously enough, the more difficult, recondite, and perplexing the
questions or hypotheses are, such, for instance, as those about
organic Nature, the more impatient they are of suspense. Sometimes,
and evidently in the present case, this impatience grows out of a fear
that a new hypothesis may endanger cherished and most important
beliefs. Impatience under such circumstances is not unnatural, though
perhaps needless, and, if so, unwise.

To us the present revival of the derivative hypothesis, in a more
winning shape than it ever before had, was not unexpected. We wonder
that any thoughtful observer of the course of investigation and of
speculation in science should not have foreseen it, and have learned
at length to take its inevitable coming patiently; the more so as in
Darwi