From H. B. Brady   18 October 1871

My dear Sir,

I have just returned from a little tour in the United States. Whilst at Boston—Prof Shaler¹ shewed me much kindness and one day when talking after dinner at his home I elicited the fol⁠⟨⁠lowing⁠⟩⁠ circumstances which, unless they are already well known to you, will I think be of much interest— if known, no harm is done,— to me they were quite new, but that might easily be. ⁠⟨⁠    ⁠⟩⁠ I manifested some ⁠⟨⁠curi⁠⟩⁠osity as to what the rattle of the ⁠⟨⁠    ⁠⟩⁠ snake really sounded like— ⁠⟨⁠    ⁠⟩⁠ only by the shaking of the ⁠⟨⁠    ⁠⟩⁠ skins one sees in European museums. He replied—in reality it is such a sound as you might imagine the dried specimen to produce if hung or a tuning fork or if by any other means a musical rythm could be imparted to it— in fact (he added) knowing rattlesnakes as well as I do, I could ⁠⟨⁠    ⁠⟩⁠ now, distinguish their ⁠⟨⁠    ⁠⟩⁠ from the whirr of the g⁠⟨⁠  ⁠⟩⁠ so common in the west.² I suggested that there was wonderful significance in this fact from a Natural Selection point of view & to this he not only assented but said it had long appeared to him to be the real explanation.— I don’t know how far this observation may be original—but I told Prof. Shaler I sh^d. transmit it to you on my return on the chance of its being of value—, the rattle snake having been regarded by many as a difficulty in the way of the natural selection doctrine.³

I met my friend Mr. Pryor⁴ of Trin. College at Philadelphia again a little more than a fortnight ago at the 5^th Ave. Hotel at New York.— Your sons were with him & well;⁵ but as chance had it, though a good deal with Mr Pryor I never met them personally.

Yours very truly | Henry B. Brady.

Charles Darwin Esq MA. F.R.S. | &c. &c. &c.