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Darwin Correspondence Project

From Leonard Darwin   28 November 1877

Brompton Barracks | Chatham

Nov. 28th. 77

Dear Father

I enclose the calculations; but see my remarks on one of them.1 I am nearly sure that the yellow glass in that cover was originally from one of those old wooden frames that you had years ago. The glass was broken and I had it put in that cover for some experiment of yours but at that time you did not use it.

Judson’s crimson dye is the dye used for that gelatine; I believe nothing that lets light through, altogether stops the actinic effects of light, but I should be almost certain that that gelatine would stop it as much as any colour would do so. After you have done your experiments with the gelatine, I could try, very roughly, how much of the actinic rays for silver salts were stopped. If you want any more of those coloured sheets you had better let me have them made here.2

I am so glad they have had a fine day for the wedding, it would have been dismal in rain.3 I shall be home on Saturday

Your affec son | L. Darwin


The enclosure has not been found.
Judson’s dyes were water-soluble dyes with a wide variety of uses in the home and garden (see an 1874 advertisement in Beeton 2014, p. [xii]). CD may have been experimenting with different ways of stopping light from reaching the leaves of plants; see Movement in plants, p. 467.
William Erasmus Darwin and Sara Sedgwick were married on 29 (not 28) November 1877 (Emma Darwin’s diary (DAR 242)).


Beeton, Samuel Orchart. 2014. Beeton’s gardening book. Containing such full and practical information as will enable the amateur to manage his own garden. (Reprint of the 1874 edition.) Cambridge: Cambridge University Press.

Movement in plants: The power of movement in plants. By Charles Darwin. Assisted by Francis Darwin. London: John Murray. 1880.


LD is supplying coloured-glass light filters for CD’s experiments.

Letter details

Letter no.
Leonard Darwin
Charles Robert Darwin
Sent from
Brompton Barracks, Chatham
Source of text
DAR 186: 32
Physical description
ALS 3pp

Please cite as

Darwin Correspondence Project, “Letter no. 11256,” accessed on 4 June 2023,