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Darwin Correspondence Project

To G. H. Darwin   18 [October 1877]1



My dear G.

Will you be so kind as to read the enclosed to Maxwell (or explain what I want) & ask him from me, whether he will be so very kind as illumine me, if he possibly can.—2 I am so very glad to hear about the tides in the earth.3

Yours affect | C. Darwin

I did not think it worth while to make a fair copy of my query.


Many leaves are covered with bloom, that is with excessively minute cylinders or points of a waxy substance. This retains a layer of air, so that if the leaf is submerged it looks coated with silver, & some leaves may be kept submerged for a week, & when taken out of water are quite dry. If the bloom is sponged off a gathered leaf, & it is hung in the air it dries much quicker than one with the bloom on it. Yet I cannot believe that the sponging can remove the wax out of the excessively minute pores through which it is secreted. Why then does a sponged leaf dry quicker? Is is possible that the layer of air entangled or in contact with the little waxy points, parts with its vapour of water more slowly than does a layer of air in contact with a sponged leaf? Can the diffusion of the vapour from the leaf be thus checked?4

C. Darwin


The month and year are established by the relationship between this letter and the letter from G. H. Darwin, 23 October 1877.
James Clerk Maxwell was a fellow of Trinity College, Cambridge, and professor of experimental physics; George Darwin was also a fellow of Trinity College.
George was investigating the consequences for the age of the earth of the supposition that the earth was composed of a viscous or imperfectly elastic matter, and thus subject to tides in its interior; his paper was published in 1878 (G. H. Darwin 1878). See also Smith and Wise 1989, pp. 597–602. He possibly mentioned his work in a letter that has not been found.
According to his journal, CD spent the latter part of 1877 working on bloom (see Appendix II); he never published the results of his investigation. See also letter to Fritz Müller, 14 May 1877 and n. 2.


Sends a query he would like GHD to put to Clerk Maxwell: why does a sponged leaf dry more rapidly, although sponging cannot remove the waxy bloom from the minute pores through which it is secreted?

Is very glad to hear about tides in the earth.

Letter details

Letter no.
Charles Robert Darwin
George Howard Darwin
Sent from
Source of text
DAR 210.1: 61–2
Physical description
ALS 1p, encl Amem 2pp

Please cite as

Darwin Correspondence Project, “Letter no. 11008,” accessed on 4 June 2023,