My dear Häckel

I must send you a few words to thank you for your interesting &, I may truly say, charming letter.¹ I am delighted that you approve of my book, as far as you have read it. I felt very great difficulty & doubt how often I ought to allude to what you have published.² Strictly speaking, every idea, altho’ occurring independently to me, if published by you previously, ought to have appeared as if taken from your works. But this w^d have made my book very dull reading; & I hoped that a full acknowledgement at the beginning w^d suffice.³ I cannot tell you how glad I am to find that I have expressed my high admiration of your labours with sufficient clearness,— I am sure that I have not expressed it too strongly. I cordially admire your devoted zeal for science, which has led you to prefer staying at Jena, instead of accepting the grand position at Vienna, so that you might do more original work.⁴ But you must have felt this offer as a highly gratifying honour. The only man whom I have known in England, who under similar circumstances w^d have acted as you have, was our illustrious Faraday—⁵ We had a good laugh at Jena being at least bigger than Down.

When shall we see you here again?⁶ It w^d give us all great pleasure, & my wife desires her very kind remembrances to you—

You will be glad to hear that my book has sold largely, viz 2500 copies in the first week & now they are printing 1500 more. I expect that I shall get very much abused for it, & I grieve to say that I have already detected 2 or 3 bad blunders.⁷

I wish you all success in y^r interesting researches on the spunges & in every thing else which you may undertake—⁸

Believe me | my dear Häckel | yours very sincerely | Charles Darwin