From C. H. Blackley   7 July 1873

Dear Sir,

My best thanks to you for the copy of D^r Wyman’s book you have been kind enough to send me.¹ I shall prize it very much because it comes from you. I saw the advertisement of it, for the first time, a couple of weeks or so after my own book² was published and at once asked my bookseller to send for a copy. This I have had by me about a month, and after having carefully read it am very much pleased with it. I regret that I did not know of the book before the later chapters in my own were written as I think many of the facts D^r Wyman gives would have helped to strengthen my position.

Now that I have the copy you have been kind enough to send me I shall send my own to D^r Phœbus, of Giessen, who I think must not have seen the work or he would have named it in a letter I had from him a few weeks ago.³

It may perhaps interest you to know that it is to your observations on the distances to which dust may be carried by atmospheric currents that my experiments at high altitudes are mainly owing. I had long had the idea that such experiments might reveal something curious; but it was only after reading your Narrative of the Voyage of the Beagle (which I did in 1864) that the idea fairly took, and kept, possession of me until I had worked it out in the way you will find described.⁴ If, after reading my book, you have, amidst your many engagements, time to pen a line and tell me what you think of the results of the experiments at high altitudes I shall be glad to have a line;⁵ but do not let me trespass too much on your valuable time because I do not forget that I am an entire stranger to you.

Again thanking you for your kindness. | I Remain Dear Sir | Yours Very Truly | Cha^s H Blackley

Cha^s Darwin Esq M.A. F.R.S. &c