If [he said] the expectation raised by the splints of horses that, in some ancestor of the horses, these splints would be found to be complete digits, has been verified, we are furnished with very strong reasons for looking for a no less complete verification of the expectation that the three-toed Plagiolophus-like “avus” of the horse must have been a five-toed “atavus” at some early period.

[Six years afterwards, this forecast of paleontological research was to be fulfilled, but at the expense of the European ancestry of the horse.  A series of ancestors, similar to these European fossils, but still more equine, and extending in unbroken order much farther back in geological time, was discovered in America.  His use of this in his New York lectures as demonstrative evidence of evolution, and the immediate fulfilment of a further prophecy of his will be told in due course.

His address to the Cambridge Y.M.C.A, “A Commentary on Descartes’ ’Discourse touching the method of using reason rightly, and of seeking scientific truth,’” was delivered on March 24.  This was an attempt to give this distinctively Christian audience some vision of the world of science and philosophy, which is neither Christian nor Unchristian, but Extra-christian, and to show] “by what methods the dwellers therein try to distinguish truth from falsehood, in regard to some of the deepest and most difficult problems that beset humanity, “in order to be clear about their actions, and to walk sure-footedly in this life,” as Descartes says.  For Descartes had laid the foundation of his own guiding principle of “active scepticism, which strives to conquer itself.”

[Here again, as in the “Physical Basis of Life,” but with more detail, he explains how far materialism is legitimate, is, in fact, a sort of shorthand idealism.  This essay, too, contains the often-quoted passage, apropos of the] “introduction of Calvinism into science.”

I protest that if some great Power would agree to make me always think what is true and do what is right, on condition of being turned into a sort of clock and wound up every morning before I got out of bed, I should instantly close with the offer.  The only freedom I care about is the freedom to do right; the freedom to do wrong I am ready to part with on the cheapest terms to any one who will take it of me.

[This was the latest of the essays included in “Lay Sermons, Addresses and Reviews,” which came out, with a dedicatory letter to Tyndall, in the summer of 1870, and, whether on account of its subject matter or its title, always remained his most popular volume of essays.

To the same period belongs a letter to Matthew Arnold about his book “St. Paul and Protestantism.”]

My dear Arnold,

Many thanks for your book which I have been diving into at odd times as leisure served, and picking up many good things.

One of the best is what you say near the end about science gradually conquering the materialism of popular religion.