WCP4996

[1]¹ [p. 16]

"9, St. Mark's Crescent, N.W., March 20th, 1870.

"Dear Sir,—In yours of yesterday you imply that Mr. Walsh's decision is an improper one, and that I know it; and that the fact proved by the trial at the Bedford River is worthless and inconclusive, and that I know it. Now I think you will, on consideration, see that it is not fair or honourable to impute to me a belief I have never acknowledged, and which I most emphatically deny and protest against. I firmly believe that the result of the trial proved all you ever asked me, or I ever undertook to prove; and that Mr. Walsh's decision is the only one an honest and sensible man could come to.

"You should remember that when, in answer to your request, I sent you a sketch of what I was going to show you, and how, you replied—'I am perfectly satisfied with your proposed plan. It cannot fail to be thoroughly convincing one way or the other.' The plan actually adopted for convenience, with your and Mr. Carpenter's full concurrence—(as shown by a sketch drawn by myself in Mr. Carpenter's notebook, at his request, on the Friday evening before the trial, and agreed by him and [2] [p. 17] you as perfectly satisfactory, but which sketch he has declined to exhibit since, and has not sent in to Mr. Walsh)—was essentially the same, yet you now say the experiment is worthless and proves nothing! What will the public say if these two letters are published?

"Now for the assertions and challenges in your pamphlet you were so good as to send me. Your proposed further tests are some very good, some quite worthless. All those which in any way depend on an apparent slope up or down, as judged of by theunaided eye, are utterly worthless; because, of all things, the eye is least able to judge accurately of a level, and if a line deviated as much as eight feet instead of only eight inches in a mile, I would defy you to tell by the eye alone if it were level, or sloped up or sloped down.

"The good tests are those which propose to determine differences of level or position by the use, either of a first-rate spirit-level, or signals which can be brought to range accurately in a line.

"First. The test proposed at p. 5, to place a spirit-level at the middle station, and take a sight both ways to Welney Bridge and Old Bedford Bridge (not Welche's Dam as you state) the water at the two ends would certainly be shown to be about five feet below the horizontal straight line touching the water at the middle station. The only difficulty would be in getting the level placed high enough to be above the vapours and unequally heated air close to the ground; but I have no doubt, if it were placed on the elevated towing path, its height above the water would be about five feet less than the height of the points on the two bridges cut by the cross-hair, which determines the true level line.

"2nd. As to the continuation of the curve beyond the three miles in each direction. This is also a good experiment, and I maintain that a signal staff placed one mile further off than either bridge, would show the water there to be eight or nine feet below that at themiddle station, and at two miles further off, fourteen or fifteen feet, as it should be if the curve continues—not less than at the Bridge, as it should be if your theory of a series of short curves, thus-[sketch of a series of humps] is true.

"3rd. The test of the lamp (p. 8) 18 inches above the water on a clear night at one Bridge, being visible by an eye or telescope situated, say three feet above the water at the other Bridge six miles distant. I maintain that it would not be visible; while, at the same time, it would be distinctly visible from the Bridge at an elevation of about fifteen feet.

"Now, on each or all of these three points I am ready, after the present wager has been finally settled, to meet you on any fair terms you may propose, the umpire being any well-known civil engineer, surveyor, optician, or scientific man—the questions all being simple matters of fact, which it requires merely good eyesight, some knowledge of instruments and experiment, and a true tongue, to pronounce upon justly.

"I remain, dear Sir, yours very faithfully,

"ALFRED R. WALLACE.

"John Hampden, Esq."