Photographic Researches and Portraiture 309
ordinary reading distance as 12 inches, a row of five dots each 3 0 o th of an inch in diameter arranged on the page of a book would be like an almost invisible fine and continuous line. A row of 300 dots to the inch will look at a foot like a continuous line, but far fewer dots are interpreted by the imagination as a line. The ordinary cyclostyle works by dotting and has about 140 dots to the inch; the usual half-tone engraving is produced also by dots, but without a lens the illustration appears continuous in its tones and shading. Galton found that with only 50 dots to the inch he could reproduce a profile which many persons to whom it was shown failed to discriminate from an ordinary woodcut. 250 to 350 points gave exceedingly well the profile of a Greek girl copied from a gem'.
Taking his points at equal distances Galton found that the direction from one point to the next could be in most cases adequately given by the points of the compass, the top of the paper being treated as north. He takes the letter a to represent north, b for north-north-east, c for north-east and so on in order up to p. This presumed, it is possible to represent any profile by a formula. Letters beyond a to p give points of reference or mark by a sort of bracket points not to be drawn in as when we pass from brow to eye. For convenience Galton breaks up' his directional letters into words of five letters each. Thus the profile of the Greek girl involved about 400 letters or 80 words, and might have been sent by telegram. In 1893 it would have cost about £8 to cable it across the Atlantic. Galton illustrated by examples the accuracy with which such portraits, maps or plans could be reproduced. In a postscript added to the printed lecture he gives a coordinate system which allows 9f somewhat greater exactness, but it requires two numbers to each direction; at the same time it allows variety in the length of the steps.
The whole paper is very characteristic of its author; it leads us from psychological theory to a practical end, the sending of portraits by telegraph ; but beneath the whole we find Galton really working at the idea of inherited resemblance as measured by the degree of likeness in the formulae for the profiles of relatives.
We have noted in our first volume that the Galton family was portrayed in a considerable number of very characteristic silhouettes. When Francis Galton turned to the problems of quantitatively measuring resemblance and of indexing portraits, he was compelled by the nature of his subject to deal chiefly with profiles, and from this standpoint he recognised_the great value of the silhouette. No doubt thinking of his own family portraits, he addressed two letters to the editor of The Photographic News2. Silhouettes, he tells the readers of that journal,
"were very familiar to those who lived in the pre-photographic period. They were quickly cut out of paper by a deft hand with a small keen pair of scissors, and at least one of the many operators in this way ranked as an artist capable of making excellent likenesses3. The paper
' This profile, about 12 inches high, was in the Galtoniana, and probably still is, but could not be found recently for reproduction here.
2 July 15th and July 22nd, 1887.
3 No doubt Edonard, who did the Galton and Darwin families. See our Vol. i, Plates IV, XVII, and XXXIV.