To Francis Galton 13 January [1876]1
Jan 13
My dear Galton
I again thank you heartily for the immense labour which you have taken for me.— I will publish entirely your “Report on general value of results” in my introduction”, & as I before said it will add very greatly to the value of my book.— I will send you a proof of the sheet whenever it is printed, though this may not be for a very long time.—2
From what you say about ratio of 100 to 80, I may mention that I measured 73 crossed & 73 s. fer plants of Ipomœa, & their mean worked out in my rough way is as 100 to 77.3 But I have been thinking for some days that I wd get the mean of all my plants, & will see if I can get my courage up for such a task.— It is too gigantic a an undertaking to begin again experimenting.
I have one question You say in last paragraph of your Report about “a few of the tallest plants”, that they “tell their own story clearly”: my sole object has been to show that the crossed plants best the s. f. when grown under similar conditions.— Now is this the “story” to which you refer, because if so your opinion is of value to me, & I shd like to make your words clearer. It seemed to me when experimenting that the plan of measuring only the tallest plants had the great advantage of eliminating on both sides all sickly dwarfed & injured plants.— I do not see that for my purpose it wd be of any great use to get G. to do all of the “tallest plants”, but I will send him some time your mathematical M.S.4
(Now with respect to the mean heights, I will say in introduction, that I merely added up the heights of all plants of each species & divided them by their number, without using any of the refinements of statistical science. But here comes an odd thing, I have added my rough mean in pencil to yours & you will see in the enclosed slip (which please return) that in 6 out of the 7 cases I make the superiority of crossed over the s. f. less than you do by some 1 to 4, generally by 3.5
I am extremely glad to find that my results are fallen out on the side of cross⟨ ⟩ Do you understand the cause of this? I will in my text under each of the 7 species give your results, & refer to your Report in my Introduction to show how you worked out your means, as this I presume will be sufficient though, I do not understand how it has been done.6 But I am astonished that the common rough way of taking a mean differs so much from your refined methods. It wd be a frightful job, to send all my Tables to some professional calculator to have accurate means taken, as I shd have to alter more or less all my M.S. & the notes; & I hope you do not think this necessary; please tell me what you think.—
There is one point on which you do not touch in your last letter viz ratio of variability in height between the crosses & s. fert plants: I send back your 2 former notes, to remind you, & please let me have them back.—7 Perhaps these go for nothing now that you know that all the plants were measured instead of, as you formerly thought to the selected tallest plants. If your remarks still hold good in any of the cases I shd be very glad to quote a few sentences from you on this subject, stating to what species you refer. I was much struck with impurity in colour of flower & in height of those s. f. plants of Petunia which grew in a long row out of doors, though that does not hold, as you say, with the plants of Petunia in the pots, & which fact I think I can explain.8
This whole subject of variability of height is so much beyond my scope, that without you can give me a sentence, I will pass it over, except just referring to the impurity, as judged by the eye alone of the P. out of doors. Nor do I think that I will ask George to work out other cases, as I shall be sure to get into some jumble.
If you will have the patience to read this unconscionably long letter & answer my queries as far as you can, I will promise to give no more trouble, & most cordially again thanking you—remain | Yours very sincerely | C. Darwin
Have you seen a R in last Frasers on the Unseen U. it seems to me excellent sign E.C. Do you know author?9
Footnotes
Bibliography
Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.
Cross and self fertilisation: The effects of cross and self fertilisation in the vegetable kingdom. By Charles Darwin. London: John Murray. 1876.
ODNB: Oxford dictionary of national biography: from the earliest times to the year 2000. (Revised edition.) Edited by H. C. G. Matthew and Brian Harrison. 60 vols. and index. Oxford: Oxford University Press. 2004.
Wellesley index: The Wellesley index to Victorian periodicals 1824–1900. Edited by Walter E. Houghton et al. 5 vols. Toronto: University of Toronto Press. London: Routledge & Kegan Paul. 1966–89.
Summary
Thanks FG for his report [on the statistical validity of CD’s experiments; see Cross and self-fertilisation, pp. 16–18]. Discusses FG’s comments, his own experiments, and the means by which the results may be analysed.
Letter details
- Letter no.
- DCP-LETT-10357
- From
- Charles Robert Darwin
- To
- Francis Galton
- Sent from
- Down
- Source of text
- DAR 202: 54
- Physical description
- ADraftS 5pp
Please cite as
Darwin Correspondence Project, “Letter no. 10357,” accessed on 26 September 2022, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-10357.xml
Also published in The Correspondence of Charles Darwin, vol. 24