The Bedford Canal Experiments
The classic Flat Earth water convexity experiments described in the book Earth Not a Globe by Samuel Birley Rowbotham. Rowbotham lives near the canal and performs the experiment numerous times over a number of years. Of special interest, in regards to the subject of refraction, we look at the second experiment.
From Experiment 2 of Earth Not a Globe we read:
“ Along the edge of the water, in the same canal, six flags were placed, one statute mile from each other, and so arranged that the top of each flag was 5 feet above the surface. Close to the last flag in the series a longer staff was fixed, bearing a flag 3 feet square, and the top of which was 8 feet above the surface of the water--the bottom being in a line with the tops of the other and intervening flags, as shown in the following diagram, Fig, 4. ”
“ On looking with a good telescope over and along the flags, from A to B, the line of sight fell on the lower part of the larger flag at B. The altitude of the point B above the water at D was 5 feet, and the altitude of the telescope at A above the water at C was 5 feet; and each intervening flag had the same altitude. Hence the surface of the water C, D, was equidistant from the line of sight A, B; and as A B was a right line, C, D, being parallel, was also a right line; or, in other words, the surface of the water, C, D, was for six miles absolutely horizontal.
If the earth is a globe, the series of flags in the last experiment would have had the form and produced the results represented in the diagram, Fig. 5. The water curvating from ”
“ C to D, each flag would have been a given amount below the line A, B. The first and second flags would have determined the direction of the line of sight from A to B, and the third flag would have been 8 inches below the second; the fourth flag, 32 inches; the fifth, 6 feet; the sixth, 10 feet 8 inches; and the seventh, 16 feet 8 inches; but the top of the last and largest flag, being 3 feet higher than the smaller ones, would have been 13 feet 8 inches below the line of sight at the point B. ”
On analysis of this experiment, if the earth were a globe, one important remark would be that it is quite the coincidence that the flags all experienced the Flat Earth refraction effect, one by one, all the way down to the end, which projected each flag into the air at the exact height they needed to be at in order to make things look flat in accordance with the distance looked across and the height of the observer.
The English Mechanic
From The English Mechanic, a scientific journal:
“ Bedford Canal, England. A repeat of the 1870 experiment
"A train of empty turf-boats had just entered the Canal from the river Ouse, and was about proceeding to Ramsey. I arranged with the captain to place the shallowest boat last in the train, and to take me on to Welney Bridge, a distance of six miles. A good telescope was then fixed on the lowest part of the stern of the last boat. The sluice gate of the Old Bedford Bridge was 5ft. 8in. high, the turf-boat moored there was 2ft. 6in. high, and the notice board was 6ft. 6in. from the water.
The sun was shining strongly upon them in the direction of the south-southwest; the air was exceedingly still and clear, and the surface of the water smooth as a molten mirror, so that everything was favourable for observation. At 1.15 p.m. the train started for Welney. As the boats gradually receded, the sluice gate, the turf-boat and the notice board continued to be visible to the naked eye for about four miles. When the sluice gate and the turf-boat (being of a dark colour) became somewhat indistinct, the notice board (which was white) was still plainly visible, and remained so to the end of six miles. But on looking through the telescope all the objects were distinctly visible throughout the whole distance. On reaching Welney Bridge I made very careful and repeated observations, and finding several men upon the banks of the canal, I called them to look through the telescope. They all saw distinctly the white notice board, the sluice gate, and the black turf-boat moored near them.
Now, as the telescope was 18in. above the water, The line of sight would touch the horizon at one mile and a half away (if the surface were convex). The curvature of the remaining four miles and a half would be 13ft. 6in. Hence the turf-boat should have been 11ft., the top of the sluice gate 7ft. 10in., and the bottom of the notice board 7ft. below the horizon.
My recent experiment affords undeniable proof of the Earth's unglobularity, because it rests not on transitory vision; but my proof remains printed on the negative of the photograph which Mr.Clifton took for me, and in my presence, on behalf of J.H.Dallmeyer, Ltd.
A photograph can not 'imagine' nor lie!" ”
From "The Flat Earth: another Bedford Canal experiment" (Bernard H.Watson, et al), ENGLISH MECHANIC, 80:160, 1904
Weather and Wave Conditions
In the chapter On the Dimensions of Ocean Waves, Rowbotham explains that the above is effected by wind and water conditions. The reproduction woks best in fine weather:
“ It is well known that even on lakes of small dimensions and also on canals, when high winds prevail for some time in the same direction, the ordinary ripple is converted into comparatively large waves. On the "Bedford Canal," during the windy season, the water is raised into undulations so high, that through a powerful telescope at an elevation of 8 inches, a boat two or three miles away will be invisible; but at other times, through the same telescope the same kind of boat may be seen at a distance of six or eight miles.
During very fine weather when the water has been calm for some days and become as it were settled down, persons are often able to see with the naked eye from Dover the coast of France, and a steamer has been traced all the way across the channel. At other times when the winds are very high, and a heavy swell prevails, the coast is invisible, and the steamers cannot be traced the whole distance from the same altitude, even with a good telescope.
Instances could be greatly multiplied, but already more evidence has been given than the subject really requires, to prove that when a telescope does not restore the hull of a distant vessel it is owing to a purely special and local cause ”