cess of evolution has extended, but accepts the
computation of the physical geologist and the physicist, whatever that
may be.

[Sidenote: and philosophy]

Evolution as a philosophical doctrine applicable to all phenomena,
whether physical or mental, whether manifested by material atoms or by
men in society, has been dealt with systematically in the 'Synthetic
Philosophy' of Mr. Herbert Spencer. Comment on that great undertaking
would not be in place here. I mention it because, so far as I know, it
is the first attempt to deal, on scientific principles, with modern
scientific facts and speculations. For the 'Philosophic positive' of
M. Comte, with which Mr. Spencer's system of philosophy is sometimes
compared, though it professes a similar object, is unfortunately
permeated by a thoroughly unscientific spirit, and its author had no
adequate acquaintance with the physical sciences even of his own time.

* * * * *

The doctrine of evolution, so far as the present physical cosmos is
concerned, postulates the fixity of the rules of operation of the
causes of motion in the material universe. If all kinds of matter are
modifications of one kind, and if all modes of motion are derived from
the same energy, the orderly evolution of physical nature out of one
substratum and one energy implies that the rules of action of that
energy should be fixed and definite. In the past history of the
universe, back to that point, there can be no room for chance or
disorder. But it is possible to raise the question whether this
universe of simplest matter and definitely operating energy, which
forms our hypothetical starting point, may not itself be a product of
evolution from a universe of such matter, in which the manifestations
of energy were not definite--in which, for example, our laws of motion
held good for some units and not for others, or for the same units at
one time and not at another--and which would therefore be a real
epicurean chance-world?

For myself, I must confess that I find the air of this region of
speculation too rarefied for my constitution, and I am disposed to
take refuge in 'ignoramus et ignorabimus.'

[Sidenote: Other achievements in physical science.]

The execution of my further task, the indication of the most important
achievements in the several branches of physical science during the
last fifty years, is embarrassed by the abundance of the objects of
choice; and by the