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280   Life and Letters of Francis Galton

near approach -to the earth, and that the possibility of exchanging signals with Mars was then discussed in the newspapers; it was considered not impossible,. if enormously difficult, to send signals. But there was a general conclusion that if sent, the only thing that could be learnt from them would be that there existed observant, intelligent and mechanical people capable of great enterprises on the other planet. Galton thought that much more might be achieved, and that an intrinsically intelligible system of. signals could be devised, if the people on the other- planet were equally advanced with ourselves in pure and applied science. He amused himself accordingly in thinking out the ground plan of the present paper, but laid it aside for four years during which the craze about Mars died out, "being cooled by copious douches of astronomical common sense. Then, in 1896, came an attack of gastric catarrh, which developed into more serious trouble owing to a visit to Kew-to attend the Observatory-with a temperature of 102. Galton was invalided to Wildbad and its hot baths, and amid their relaxing accompaniments, being able to work only in a desultory fashion, he wrote up his paper on signals from Mars'. The main point of this paper is the building up of a system of signals from which ultimately pictures can be constructed. It is half humorous and half serious. It starts with the idea that arithmetical and mathematical notions will be common knowledge of both planet's inhabitants. Signals of 1,, 22 and 5 seconds are given and termed dot, dash, line. These lead up to a system of numerals. Then comes the ratio of the circumference of a circle to its diameter, the value of the familiar ir. Thence the ratio of the circumference to the radius of the various regular polygons, which introduces signals for the polygons. The 24-sided regular polygon is then indicated as a method of direction, and so angles all round the 360° are gradually learnt in the same way as are the points of a compass, but direction of lines and length of lines being given it becomes possible to give signals indicating a picture by successive "stitches" of definite lengths in definite directions. That is to say, Galton has reached the picture formula of his lecture on the "Just Perceptible Difference" (see the following Chapter, p. 307). But once it is possible to signal pictures, all becomes possible. It becomes possible to indicate motion, and motion will enable one to indicate signals for action, i.e. verbs. Such, very briefly, is the outline of Galton's system of star signals

"It would be tedious, and is unnecessary to elaborate further, for it must be already evident to the reader that a small fraction of the care and thought bestowed, say, on the decipherment of hieroglyphics, would suffice to place the inhabitants of neighbouring stars in

intelligible communication if they were both as far advanced in science and arts as the civilised nations of the earth are at the present time. In short, thatt an efficient interstellar language admits of being established under these conditions, between stars that are sufficiently near together for signalling purposes."

1 Both Galtons were much depressed during this year. Emily Gurney died, and Sir William Grove died on the anniversary of the Galtons' wedding day (August 1st). The season was very wet and Galton suffered much from colds; he complained for the first time (aged 74!) that his brain power was not as vigorous as formerly, that he could not work quickly and that his deafness interfered with his committees.