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Down, Oct. 12th. [1866] My Dear Mr Pritchard,—I have read with much interest your sermon, with its appendices, & I thank you sincerely for having sent it me.

I should be a very cross-grained man to object to a single word that you have said. You pay me the most elegant compliments, and attack me with much spirit and force. Even if I could you would not thank me for making a long defence; but I may make two remarks. When I refer to the extremely simple eyes of the articulata (i.e., insects, spiders, etc.), you translate this into the human eye. Should there be a second edition, I hope you will correct this, for I have always spoken of the human eye as the pinnacle of difficulty.

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You speak of the necessity of various parts of the eye changing simultaneously in order that it may become adapted for even slightly changed work; but many a short-sighted person can see an object distinctly at a distance which renders the image confused to others.

What a very curious case about the increasing length of day! I have that profound respect for mathematics which profound ignorance gives, but I cannot help observing that when applied to uncertain subjects, such as geology, it gives as uncertain results as geologists arrive at by other means; for instance, how Thomson and others differ about the thickness of the crust of the earth and the rate of cooling.

My son George has been much interested by your sermon, and begs to be very kindly remembered to you.—

With my best thanks, pray believe me, yours very sincerely,

Ch. Darwin

That is a very foolish episode of mine about the Wealden, and was struck out in later editions.