To Leonard Horner   [January 1847]¹

My dear M^r Horner.

Your most agreeable praise of my Book² is enough to turn my head; I am really surprised at it, but shall swallow it with very much gusto.

With respect to the inclination of the lava-streams, it would indeed as you say be utterly impossible to measure them with any clinometer. The river was carefully mapped, so that the distance between any two points was known: then I measured at (A) the height of lava-stream above the river & the fall of the river having been ascertained the height above the sea could be approximately known.

Then the same operation being done at B, the difference in height made a triangle & the angle is most easily calculated by trigonometry. Being out of practise my Brother calculated them.³ As I say, these measurements though not absolutely correct, from the data not being so, cannot be far wrong.

E. de Beaumont measured the inclination with a sextant & artificial horizon, just as you take the height of the sun for latitude.—⁴

With respect to my Journal,⁵ I think the sketches in the second edition are pretty accurate; but in the first they are not so, for I foolishly trusted to my memory, & was much annoyed to find how hasty & inaccurate many of my remarks were, when I went over my huge pile of descriptions of each locality.—

If you ever meet anyone circumstanced as I was advise them not on any account to give any sketches until his materials are fully worked out.

With many thanks for the pleasure your commendations have given me, believe me | Dear M^r Horner | Yours very truly | C. Darwin.

What labour you must be undergoing now; I have wondered at your patience in having written to me two such long notes. How glad M^rs. Horner will be when your address is completed.⁶

I must say that I am much pleased that you will notice my volume in your address, for former presidents took no notice of my two former volumes.⁷

I am exceedingly glad that Bunbury is going on well.—⁸