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Characterisation, especially -by Letters   565

to identify him surely. When closer still, you see the individual features clearly. I ought to have begun a stage earlier, by saying that when first he is seen at all, his face is little more than a dot and cannot be distinguished from that of any one else. You can see all these grades of resemblance in the faces of a group-photograph of any crowd. Each grade of resemblance is connected with a "critical distance." Further off it ceases. But it is not simple distance that we are concerned with, it is with distance and size, in order that what is true for a big picture shall be equally true for a miniature. Therefore the unit is the angle. The size at a distance is expressed by the angular size; the distance and area by the angular area. The particular angle I use is approximately that subtended by the disc of the sun (paled by a cloud). It is that of a breadth of 1 seen at a distance of 100, as one-tenth of an inch at 10 inches, one yard at 100 yards, and so on. It is only "Ith wider than a sun-breadth, so, wanting a word for it, I call this angle a Sol, and the square whose side is a Sol, a Square-Sol. My measure of any of the above grades of Resemblance is the number of Square-Sols at the critical distance, this being proportional to the number of just-distinguishable plots. The number of square-sols is easily determined by a low-power telescope with appropriate cross-lines in its focus, such that each little square is exactly a square-sol, and one counts the squares that cover the image. I have quite another page-full about this with which I need not bother you now. The above is a mere outline of what I am at. F. G. February 16, 1906 (aet. 84 years and 8 hours).

HOTEL DE LA RHUNE, AsCAIN, BASSES PYRENEES, FRANCE. February 18, 1906.

MY DEAR EDWARD, Part III is most clear and pleasant reading, and the results both practical and theoretical will strike everyone as first-rate. You have vastly improved Part III. Somebody will be down on "Endemic-confined to a particular district," but let that be.

I am very glad all is getting ready for your Mediterranean holiday and sincerely hope you may have none of the abominable Bay of Biscay weather that has plagued us during the past ten days, up to yesterday morning.

As regards some of your dear Mother's things,-on or about whose birthday you may receive this-you mention the engravings of Hodgson. Yes, I should be very glad to have one of them, but without the frame, as its destination will be in a portfolio. Hodgson brought me into the world 84 years ago, he advised my father on my education, I worked under him at the Birmingham Hospital, travelled, on his recommendation, with one of his pupils, afterwards Sir Wm. Bowman, lived in the house of another pupil, Professor Partridge (father of the caricaturist), when medicalising in London, and saw much of him up to his death. So he fills a large part of my recollections and I should be very glad to preserve his portrait.

The photo you send of Claverdon garden from the verandah gives a capital idea of part of the changes. I shall be most interested in the full result when I return. We stay on here, having only partly seen the neighbourhood yet owing to vile weather, but this is a land of surprises in that respect. The sun may burst out at any moment, as it has done while I was writing this; then, squalls of hail and cold and all that is unpleasant.

I wrote to Erasmus two days ago and hope to hear that he is well again. Milly and I write weekly. She told me of your kindness in asking Guy to join you, and of his very great regret that his lost arm unfitted him for sea voyages. I suppose the least bit of an arm is of much help, and he has none left, which makes the difference between what he and, say, Lord Nelson, could do on board ship. With best loves to you and M. L.

Ever affectionately, FRANCIS GALTON.

P.S. Eva would of course join, but she is at the Basque Church.

Address now: Hotel Terminus, St Jean de Luz, Basses Pyrdndes, France. February 24, 1906, Saturday.

DEAREST MILLY, Yours is just come. Yes, it is evidently Birrelligion. I had forgotten that he was the new Minister of Education. We leave here on Monday and stay loosely on at St Jean do Luz, so as to get a few days at San Sebastian. The weather with the exception of two beautiful days has been execrable, and is so now. Eva will send you a post-card about this place. I fear it is liable to inrushes of noisy French, who go up the Rhune (3000 feet) and have a grand dinner, sleep here and return to Biarritz, etc. on the morrow. One noisy party of six