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Correspondence with Charles Darwin   179

Now you may perhaps like to hear a few additional particulars about myself.' I cannot remember the time when I had not a passion for collecting,-first seals, franks, then minerals, shells etc. As far as I am conscious, the one compulsory exercise during my school life which improved my intellect was doing Euclid, and this was partly voluntary.

At Edinburgh I do not think the lectures were of any service to me; but I profited as a naturalist by observing for myself marine animals.

At Cambridge getting up Paley's Evidences and Moral Phil. thoroughly well as I did, I felt was an admirable training, and everything else bosh.

My education really began on board the "Beagle."

I must add that my son Frank said he could safely give as my character, "sober, honest and industrious."

And now I want to ask you a question: if I had 50 men of 2 different nations, and for some reason could not measure all, if I picked out the 10 tallest of each nation, would their mean heights probably give an approximate mean between all 50 of each nation?

I hope you will get full answers to your queries, as I dare say the results will be interesting.

My dear Galton, Yours sincerely, CH. DARWIN.

42, RUTLAND GATE, S.W. May 30/73.

MY DEAR DARWIN, I am truly obliged by the Schedule. A few others are sent, many are promised and I have much hopes of useful statistical result in many ways. All I have thus far got confirms the _belief that the families will be on the average very small. As.for what the usual education will have been, I cannot yet guess.

In reply to your query about the 50, there seems-or it may be that I am stupid-that a word is omitted, displaced or somehow wrong, because the sense is not clear and I don't know how to interpret the meaning of the phrase °`   would their mean heights probably give an approximate mean between all 50 of each nation," but the following will probably include what you want.

If nothing else could be assumed about the two nations than that the 10 tallest out of 50 taken at haphazard from A had a mean height of a', and those from B of /3', it would be impossible therefrom to deduce either:

(1) a and /3, the respective mean heights of the 50 A and the 50 B or (2) the ratio of a to /3.

But if you grouped the 10 tallest in either case according to their heights, that is, so many between 5' 10" and 5' 11", so many between 5' 11" and 6' 0" etc., it would be possible by comparing the run of these numbers with those of an ordinary Table of the Law of Error, to estimate approximately both (1) and (2).

10 is too small a number to be serviceable I should fear in this way;-100 ought to give excellent results; in any case the degree of regularity with which the numbers happened to run would be the measure of the probability of the accuracy of the results.

If you have any case you want, worked out and would send me the figures I will gladly do it. Ever sincerely yours, FRANCIS GALTON.

For the year 1874 there are no letters. Darwin was ill in September 1873, Mrs Tertius Galton (Violetta Darwin) died in February 1874, Mrs Francis Galton was very ill in September and Galton himself at Christmas with "irregular gout and influenza." Darwin's eldest son George (later Professor Sir George Darwin) takes up the correspondence.