To J. F. W. Herschel 6 June 
Down Farnborough Kent
Dear Sir John Herschel
I enclose two valves of the Ibla1 done up in damp cotton; you had better put it into spirits. I hope I made it clear that I did not wish you to waste a minute of your truly valuable time, without you feel on your own account any interest in the phenomenon: I am so wholly ignorant on such points, that I did not know whether the case was of any signification. To see the blue, a thin slice must be cut off & a tolerably high single lens used to look at it, if you think it worth looking at, if not pray throw it away.2
I fear that you must find the superintendence of the Instructions3 very troublesome. Any part of mine which you think had better be struck out shall be done & I will piece it as well as I can; but if much shortening is required it will almost require rewriting & it will render necessary all one’s virtue to take that much trouble to save the Admiralty a few pounds in using smaller type. I did not put it anything for the mere purpose of swelling mine.
Believe me | Yours sincerely | C. Darwin To Sir J. W. Herschel Bart.
Sends two valves of Ibla.
In his chapter [for Manual, Collected papers 1: 227–50], he will strike out any part that JFWH wants struck out, but if much shortening is required it will need rewriting.