ed by constant laws and confined within certain
limits_. Indefinite divergence from the original type is not possible,
and the extreme limit of possible variation may usually be reached in a
short period of time; in short, species have a real existence in Nature,
and a transformation from one to another does not exist."[50]

The whole science of Natural History is based on the existence of
distinct species, capable of being discriminated from each other by
certain characteristic marks; and the whole art of the agriculturist and
the stockbreeder proceeds on the assumption of a law, invariable in its
operation, whereby "like produces like in the vegetable and animal
worlds." The instances to which the author of "The Vestiges" refers in
support of his theory are utterly frivolous when opposed to the copious
inductions to which they are opposed; and they may all be explained
consistently with the _law of variation within definite limits_, as
stated by Dr. Whewell, or by our ignorance of all the conditions
involved in each particular case. Nor is his argument founded on the
limited range of our observation, even with its singular illustration
derived from Mr. Babbage's calculating engine, fitted to diminish, in
the slightest degree, our confidence in the general results of these
inductions; for, not to mention that it amounts to nothing more than an
appeal from what we do know to what we do not know, from knowledge to
ignorance, from the certainties of science to the mere possibilities of
conjecture, it has been well shown by Mr. Miller, that our range of
observation is not so limited as the author of "The Vestiges" would have
us to believe, since "_extent of space_ is, in a matter of this kind,
equivalent to _duration of time_. For, although no man has lived five
hundred years, so as to observe the gradual development of the oak from
the acorn in its various stages of progress, yet every man who can
survey five hundred yards of an English forest, can see the oak in every
stage of its growth, and need have no doubt as to the law of its
progressive development. And so, had there really been such a
transmutation of species as is contended for, we might expect to find,
somewhere on the vastly extended sea coasts of our islands and
continents, some specimens of plants or animals in a state of transition
from the lower to the higher forms."

We are told, indeed, in answer to this argument, that Mr. Babbage's
engine produces numb