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Darwin Correspondence Project

To J. W. Clark   9 February 1875

Down, | Beckenham, Kent.

Feb 9 75

Dear Sir

I am very much obliged to you for so kindly sending me the information on the action of fear in the iris.,—a subject about which I formerly felt great doubts1

Dear Sir | Yrs faithfully | Ch. Darwin


In Expression, pp. 303–4, CD discussed claims that fear caused the pupils to dilate, but admitted he did not have much evidence of the phenomenon. A note was added to Expression 2d ed., p. 321 n. 37, referring to information received from T. W. Clark of Southampton in letters of 25 June and 16 September 1875 on the dilation of dogs’ and cats’ pupils due to fear. The writer was, in fact, Joseph Warner Clark; see letters from J. W. Clark, 25 June [1875] and 16 September 1875.


Expression 2d ed.: The expression of the emotions in man and animals. By Charles Darwin. 2d edition. Edited by Francis Darwin. London: John Murray. 1890.

Expression: The expression of the emotions in man and animals. By Charles Darwin. London: John Murray. 1872.


Thanks for information about effect of fear on the iris.

Letter details

Letter no.
Charles Robert Darwin
Joseph Warner Clark
Sent from
Source of text
University of California, Berkeley, The Bancroft Library (BANC MSS 74/78 z)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9847,” accessed on 21 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 23