To Mrs. Lesley.

Cambridge, March 22, 1870.

It is more than a fortnight since I left you. ... I really felt a little homesick when I arrived at this uninhabited room, where no one waited to welcome me, except the old books and the old work. I did not care to brush the dust from them, and they did not seem to care whether I did or not.

. . . What does Mr. Lesley think of Mr. Alfred Wallace’s estimate of geological time in the last two numbers of “Nature”? I should like to have an evening’s talk with him about it. I like the ingenious suggestion that in the past sixty thousand years species have changed at a comparatively slow pace on account of the comparatively equable climates which astronomy indicates for this period. It is somewhat like the exception he makes in a former paper as to the changes to which the human race has been subject, and tends in the same way to shorten the estimates of the previous ages of creation. But I don’t feel so much confidence, as Mr. Wallace seems to have, in the limit of one hundred million years which the physicists set. The history of the solar system and the data derived from the mechanical theory of heat seem to me too much matters of mere guessing. The physical data are exact enough, so far as they go; but the physical history of the universe is known in too few of its elements to warrant such confident chronology, even if we leave miracle altogether out of account. To speculate exclusively on the little that we know, in place of speculating totally on our ignorance, is going to the opposite extreme. I should rather think the geologist himself entitled to the first word on the subject, or, at least, to as much time as he wants. To take the present rates of cooling and loss of force in the earth and the sun as typical and universal facts, and to calculate solely on them, is too suspiciously simple to be a probable account of nature. It smacks too much of cosmogonic theories.

I am still inclined to believe that the history of the solar system is not an entirely regular development or a simple specimen of universal progress out of an original “homogeneity” (as it is now the fashion to call the old nebula), and that science ought to free itself entirely from this unscientific prejudice which cannot be proven or tested any better than miracle, and is prompted chiefly by the impatient love of simplicity

that characterizes all transcendental speculation (either abstract or concrete), i. e. theories of inexperienced phenomena. Only the facts of life, or the histories of living organisms, show decisively a regular external order, and this, so far from being typical, is found to depend, in the last analysis, on an almost infinitely complicated, but self-conserving combination of the internal, elementary orders of nature, or laws of matter, living and dead; and it shows itself decisively only in the development of the individual organism, and but vaguely in the development or history of species.

The physical laws of nature are thus to my mind the only real types of the general order in the universe. Life builds an order out of these, which, so far from exhibiting in its stages of development an epitome of the general order, ought to be regarded, so far as evidence can guide us, as an entirely exceptional and precarious state of things, lying within the compass of natural possibilities, but far from illustrating the general results of the interactions of natural forces. These results present themselves to my imagination as they did to old Aristotle’s as an infinitely complex and confused movement, without apparent beginning or end or tendency, but showing at every turn the intimate play of action and counteraction in the balanced forces from which they spring. Gravitation and heat are the two most powerful and pervading causes of this movement; but the laws of heat are known only on one side, — its wasting action, its tendency to diffuse the mechanical energies of nature. Cosmogonic physicists, like Professor W. Thomson, assume that this is all that is to be known about it, and do not inquire what may become of it in the spaces through which it is diffused, or how a round of actions can be effected through it and the agency of gravitation which would not tend to uncompensated movements, or to that transition from one chaos to another which the modern cosmogonists assume as the general order of nature.

This scepticism of mine is now called “materialism.” It is not the same as the ancient doctrine of this hateful name, since it is not opposed to the same orthodoxy; for even orthodoxy is subject to change! Perhaps I should say something like this in the evening’s talk, if my eloquence were not checked before arriving at the last sentences by crushing objections. Now, I have it all my own way, and get safely through my peroration. Such is the privilege of letters — and sermons! but one has to imagine the applause.

I send in the same mail with this a slate for Mr. Lesley’s editorials. I find that the lead-pencil flows on the surface of it almost as freely, if not quite, as ink. Give my true love to all.