have been established beyond contravention,
that the latitude for hypothesis is much less than it once was.
Nine tenths of the guesses which might have occurred to a mediaeval
philosopher would now be ruled out as inadmissible, because they would
not harmonize with the knowledge which has been acquired since the
Middle Ages. There is one direction especially in which this continuous
limitation of guesswork by ever-accumulating experience has manifested
itself. From first to last, all our speculative successes and failures
have agreed in teaching us that the most general principles of action
which prevail to-day, and in our own corner of the universe, have always
prevailed throughout as much of the universe as is accessible to our
research. They have taught us that for the deciphering of the past and
the predicting of the future, no hypotheses are admissible which are not
based upon the actual behaviour of things in the present. Once there was
unlimited facility for guessing as to how the solar system might have
come into existence; now the origin of the sun and planets is adequately
explained when we have unfolded all that is implied in the processes
which are still going on in the solar system. Formerly appeals were made
to all manner of violent agencies to account for the changes which the
earth's surface has undergone since our planet began its independent
career; now it is seen that the same slow working of rain and tide, of
wind and wave and frost, of secular contraction and of earthquake pulse,
which is visible to-day, will account for the whole. It is not long
since it was supposed that a species of animals or plants could be swept
away only by some unusual catastrophe, while for the origination of new
species something called an act of "special creation" was necessary; and
as to the nature of such extraordinary events there was endless room for
guesswork; but the discovery of natural selection was the discovery of a
process, going on perpetually under our very eyes, which must inevitably
of itself extinguish some species and bring new ones into being. In
these and countless other ways we have learned that all the rich variety
of nature is pervaded by unity of action, such as we might expect to
find if nature is the manifestation of an infinite God who is without
variableness or shadow of turning, but quite incompatible with the
fitful behaviour of the anthropomorphic deities of the old mythologies.
By thus abstai