Russel Wallace : Alfred Russell Wallace (sic)
Regarding the Bedford Canal Experiment
(S200aa, S200ac, S200ab, and S200b: 1871)
[[p. 94]] [2760.]--The fact that the lecturer who styles himself "Parallax" still makes numerous converts, and that Mr. Hampden and Mr. Carpenter are quite unable to see the true meaning of the observations made on the Bedford canal, show, I think, that other proofs than those usually relied on are required to enable persons of a peculiar frame of mind to see the impossibility of the earth being flat. With your permission, therefore, I will point out two classes of facts which are absolutely incompatible with the flat theory, but which I do not remember to have seen adduced in any works as special proofs of the rotundity of the earth.
1. The position of the visible horizon, or that line at which the sun, moon, and stars set and rise, is an absolute test of the rival theories. If the earth is round, the sea horizon seen from a point moderately elevated above it, will be always much below the true horizontal line, while if it is a plane the same horizon will in most cases be above the horizontal line. To make this clear it will be necessary to refer to diagrams.
In Fig. 1, let A be the observer, elevated say 50ft. above the sea, and with a clear sea view on both sides, such as may be had on the North Foreland, Beachy Head, Start Point, and many other places on our coasts. If the earth be round, and of the accredited dimensions, his view will be bounded by the water at W W, between eight and nine miles distant, and though there may be high land beyond at M M., this will not be visible unless it rises above the line A W, behind which line the sun (S) will appear to set, and will become invisible. The two lines A W, A W, in directly opposite directions will both be below the horizontal line H A H.
Fig. 2 is identical with Fig. 1, but is drawn on the supposition that the earth is a plane. The observer at A will have some land higher than himself in almost every direction from him. On the N. Foreland, for instance, he will have to the right or S.E., the Alps, at a distance of 450 miles, and three miles high; and his horizon in that direction would be elevated, as shown by the line A M, which must rise above the horizontal line A H about 0° 20" (twenty minutes of arc). This is equal to the angle formed by an object three feet high at a distance of 450ft., and therefore easily to be seen by the unassisted eye. In exactly an opposite direction to the Alps will be found the mountains of North Wales, 250 miles off and more than half a mile high, making an angle above the horizon of about 0° 6", or six minutes of arc, an amount also easily seen by any one, being about that of a three foot target 500 yards off. Now as these mountains are solid and opaque objects, the sun, moon, and stars cannot be seen through them, and must therefore "set" or disappear behind them a long way above the water at W W (Fig. 2). The apparent horizon lines A M, A M, on or at which the heavenly bodies rise and set, will be considerably above the true horizontal line H A H. Here, then, we have a positive test of the two theories which any one, without instrument of any kind, can apply for himself. Almost anywhere on our south or east coasts the moon may be seen to rise or set over the sea. Let the observer notice if it first appears or disappears on the surface of the water or some distance above it. If the former, let him consult a good map of Europe, and see if in the direction of the moon there was any mountain range which ought to have hid it at a considerable distance above the water. As the moon shifts its point of rising every night, a few observations will soon settle this point; and if any number of competent observers see the moon in a given direction rising, in a clear atmosphere, not from the sea, but from a point considerably above it, and at an elevation proportionate to that of a mountain range known to be in that direction, it will be a fact, if constantly to be observed, greatly in favour of a flat earth. Such a fact, however, has never yet been recorded, and it can hardly have escaped notice till now. The other point, the elevation or depression of the apparent horizon lines (A W, A W, in Fig. 1, A M, A M, in Fig. 2) above or below the horizontal line H A H, can also be determined by any one without any instrument but a couple of sticks. I tried it last year on the North Foreland as follows:--Choosing a flat spot with an uninterrupted view right and left, I stuck up two sticks (S S') some 20 or 30 yards apart. Standing behind one of them at 0, I looked over their tops, and by cutting one shorter, I soon got the two to range exactly in a line with the distant horizon. Standing now on the other side at 0', I found the tops to range considerably above the horizon. I therefore cut a piece off the stick at S sufficient to bring the line half way down to the horizon, and then found that by changing my position from 0' to 0 the tops of the two sticks ranged clear above the horizon to an equal amount in both directions, as in the line H A H, Fig.1. If the earth had been flat a horizontal line should have cut below the visible horizon in both directions, because in both directions there was land considerably higher than that on which I stood, the mountains of Wales and Cumberland on one side, and the Alps on the other. A perfectly straight board or table might be used instead of two sticks, but being shorter this would be less accurate. It must be observed that these tests cannot be evaded by saying that the mountains are too far off to be seen, and that they are confounded with the blue haze of the lower strata of the atmosphere. For even if this were the case they would still differ from the atmosphere in being opaque, and in hiding the heavenly bodies before they reach the visible horizon. But as a fact mountains are, when high enough, distinctly seen at 300 miles distance, as in the case of the Himalayas from some of the lower mountains of India.
2. The other proof of rotundity, is the fact of the sun not being visible all over the earth at once, as it must be if the earth were a plane. Now that locomotion is so rapid and good watches so common, this can be and is tested by every traveller. Any good watch can be trusted to within five or ten minutes in a week. But in eight days a man may go from Liverpool to Halifax (N.S.), and during the voyage he will find that every day the sun rises by his watch half an hour later; and when he arrives at Halifax he will know that when his watch shows 8 o'clock a.m., his family at Liverpool will be having their breakfast with the sun shining brightly in at the window, while with him it will be pitch dark and want two hours to sunrise! So in the afternoon he will find the sun shining high above the horizon when his watch marks 8 p.m., and when he knows it is pitch dark at home and the sun has set two hours before. If he has been taught nothing about longitude and time, he may think his long-trusted watch has gone wrong; but on returning a week afterwards to Liverpool he finds it all right, and not more than a few minutes fast or slow. Now this fact, of the sun being two hours (30°) above the horizon at Liverpool at the same moment that it is as much below if at Halifax--bright sunlight at the one, pitch darkness at the other--is absolute demonstration that the earth is not a plane, for over the whole surface of a plane earth the sun must shine at the same instant. Even more convincing is it to go to Hammerfest in Norway, or any other place within the arctic circle in June; for there the sun is to be seen, for some weeks, all night long above the horizon, while in Scotland, only a thousand miles off, it dips far beneath it. Here no quibble about unknown changes in watches while travelling east or west is available, since no watch is required to show the sun shining at midnight, and day and night continuously for weeks together. The fact that these changes of time and of the sun's altitude are exactly such as to agree with the curvature of a globe 8,000 miles in diameter, proves not only that the earth is not flat, but that it is a globe of the dimensions usually assigned to it.
I think it would be interesting if you, Mr. Editor, would open your columns to receive any replies that "Parallax," Carpenter, Hampden, or any of their supporters may make to the facts here adduced; and I am sure they can have no fairer or more competent judges than the intelligent readers and correspondents of your valuable paper.
Holly House, Barking.
[We have no objection to insert any arguments in answer to Mr. Wallace, but we cannot find room for Mr. Hampden's abuse.--Ed.]
[[p. 170]] [2890.]--"Parallax" replies to my arguments by denying my facts. This is certainly going to the root of the matter, but we can hardly take his ipse dixit against the universal testimony of all practical men. He denies that the sun rises and sets at an angle of more than 90° from the zenith; but all navigators and surveyors know, not by one experiment but by thousands and tens of thousands, that it does; and in all works on navigation and geology is to be found a table of the "dip of the horizon," or the number of degrees and minutes to be added to 90° to give the angle between the zenith and the horizon for different altitudes. "Parallax" might as well maintain that the sun has twice the angular diameter of the moon, and his followers would doubtless accept his statement without ever testing it, in one case as well as the other.
In my turn I deny "Parallax's" fact of a small boat being seen six miles off by an eye only twelve inches above the water. When I placed my eye about two feet above the water at Welney-bridge, only the upper part of the arch of the Old Bedford-bridge (six miles off) was visible, the lower half being concealed by the water line. I will join "Parallax" in no experiment till I have better proof of his honesty of purpose. This may be tested by his submitting to an experiment in which any dishonesty will be detected, such as the following:--Let six coach or railway lamps be provided at, say, Welney-bridge. Let a committee of two persons (appointed by neither "Parallax" nor myself) have charge of them, and exhibit them on a clear night at a fixed hour, say for two minutes, with an interval of two minutes, six successive times, each time changing the number and position of the lamps exhibited. Let "Parallax" be stationed six miles off with his telescope (which detected the boat, flag, and man) also fixed one foot above the water, and let him note down on paper the number and position of the lamps at the six successive exhibitions. Let him and the committee send to you, Mr. Editor (that night, and without meeting each other), their respective statements to be published. If "Parallax" describes all the six positions and numbers accurately, as he must easily be able to do if his theory is sound and his former observation correct, I hereby undertake to pay all the expenses of the experiment. A friend of mine will see that the experiment is fairly conducted, as far as the position of "Parallax" and his telescope are concerned. I think all impartial readers will acknowledge that this is a fair test; the "boat" experiment, with "the public" for witnesses, could not be so. Boats are continually passing along the canal, and I would defy the most experienced observer to tell whether a boat was four miles or six miles off, or to distinguish anything accurately in the vibrating atmosphere that is almost always present in the daytime; and I can quite understand that the Norfolk "public" would readily see what they were told to see in so unaccustomed an instrument as a powerful telescope. Allow me to make another remark. If the telescope used by "Parallax" showed him an object (a man) about one foot across (and oars of a still smaller diameter) at six miles distance, the same telescope would certainly show him objects one hundred feet diameter at six hundred miles distance, the angle subtended being the same in both cases. Why, then, does not any telescope ever show the range of the Alps, less than five hundred miles from the east coast of England, and extending for more than one hundred miles across the field of view, many single mountains being miles in diameter, and the marked contrasts of dark pine forests and shining show fields being most easily visible objects. All this must be seen if the earth be a plane, and if "Parallax" saw the oars at six miles distance. How strange that of the hundreds of good telescopes upon our east coasts none have ever shown a glimpse in that direction of anything but sea and sky! Let "Parallax" take his telescope to Southend or Margate, and exhibit this beautiful sight to an admiring crowd. When he can do so we shall, many of us, become his converts.
Alfred R. Wallace.
[[p. 193]] [2935.]--In my letter last week (hastily written), it would be more intelligible to substitute in the 12th line, "elevations" or "heights," for "altitudes," the latter word being generally applied to angular measurements.
As regards your offer of a discussion with "Parallax" in your columns, I can only continue it on condition that "Parallax" keeps to the point, and fairly answers my arguments and facts, one by one, before advancing fresh ones on his own side. Unless this is strictly complied with, I must decline a useless controversy.
Alfred R. Wallace.
[It is abundantly evident that "Parallax" will not do as Mr. Wallace suggests, and therefore the controversy must cease. "Parallax" has written us, declining to make the experiment as intimated by Mr. Wallace last week, as he thinks the one suggested by himself, with boat and flag, would be the more satisfactory.--Ed.]
[[p. 220]] [2988.]--I quite agree with Mr. Proctor's excellent letter, which would, however, not have come with a good grace from me. In order that you may judge of the consistency and good faith of Mr. Hampden and his supporters, I inclose you two papers. 1. p. 17 of a pamphlet by Mr. Hampden, in which he printed my letters to him. From the marked paragraphs you will see that Mr. Hampden had proposed to me the experiment of lamps at night, and that I had agreed to it! 2. A report of experiments made for and published by Mr. Hampden, in which the most elaborate experiment is this very one of lamps, but without the precautions which could alone render it of any value.
Holly House, Barking.
[Though "Parallax" has challenged Mr. Proctor, it is not likely that Mr. Proctor will accept it. Should he decide to do so some other organ must be selected as a medium of the controversy. Mr. Wallace inclosed the documents referred to in his letter. We have also received per post several unsealed letters from Mr. Hampden, in which the characters of public men are traduced. Every one of these letters would subject Mr. Hampden to a criminal prosecution.--Ed. E. M.]