WCP4993

[1]¹ [p. 15]

"9, St. Mark's Crescent, N.W., Feb. 16th, 1870.

"Dear Sir,—I do not wish to make the least alteration in the arrangements, and the referees shall of course attend; but I certainly think, as you have written so strongly on this matter, you should be present yourself.

"Till the wind changes, I fear there will be fog in the Fens, but if it looks promising I shall go down on Monday, and if it is clear, telegraph to the referees and yourself.

"The test I am going to use is very simple and conclusive. I have prepared half a dozen signal posts, each six feet long, and with red and black circles attached to them, so as to be distinctly seen at a long distance. I shall set these up a mile apart on the water's edge, and then look along them with a powerful telescope. If the water line [2] [p. 16], is straight and flat, the tops of these poles will of course be straight and flat too; but if the earth and water has a curvature of 4000 miles radius, then the tops of the poles will be equally convex, and they will be seen rising higher and higher to the middle point, and then sinking lower and lower to the furthest one, and the amount of rising and falling will be nearly the feet and inches I have put down on the diagram on the other side. The upper figure shows what must be seen if the earth is round, the lower what must be seen if it is a plane.

"Of course the curvature shown is immensely exaggerated, but with a good telescope it will be easily seen if it exists.

"Yours very faithfully,

"ALFRED R. WALLACE.

"John Hampden, Esq."