Let A B represent the arc of water from Welney Bridge to Welche’s Dam, six miles in length; and A L the line of sight, which is now a tangent to the arc A B; the point of contact, T, is 1 mile from the eye of the observer at A; and from T to the boat at B is 5 miles; the square of 5 miles multiplied by 8 inches is 200 inches, or, in other words, that the boat at B would have been 200 inches or above 16 feet below the surface of the water at T; and the flag on the boat, which was 3 feet high, would have been 13 feet below the line-of-sight, A T L!!
From this experiment it follows that the surface of standing water is not convex, and therefore that the Earth is not a Globe! On the Contrary, this simple experiment is all-sufficient to prove that the surface of the water is parallel to the line-of-sight, and is therefore horizontal, and that the Earth cannot be other than a Plane! In diagram [Figure 3] this is perfectly illustrated.
FIG. 3.
A B is the line-of-sight, and C D the surface of the water equidistant from or parallel to it throughout the whole distance observed.
Although, on account of the variable state of the water, objections have been raised to experiments made upon the sea-shore to test the convexity of the flood or ebb-tide level, none can be urged against observations made from higher altitudes. For example,—the distance across the Irish Sea between Douglas Harbour, in the Isle of Man, and the Great Orm’s Head in North Wales is 60 miles. If the earth is a globe, the surface of the water would form an arc 60 miles in length, the centre of which would be 1,944 feet higher than the coast line at either end, so that an observer would be obliged to attain this altitude before he could see the Welsh coast from the Isle of Man: as shown in the diagram, [Figure 4].
FIG. 4.
It is well known, however, that from an altitude not exceeding 100 feet the Great Orm’s Head is visible in clear weather from Douglas Harbour. The altitude of 100 feet could cause the line of sight to touch the horizon at the distance of nearly 13 miles; and from the horizon to Orm’s Head being 47 miles, the square of this number multiplied by 8 inches gives 1472 feet as the distance which the Welsh coast line would be below the line of sight B C.—A representing the Great Orm’s Head, which, being 600 feet high, its summit would be 872 feet below the horizon.
Many similar experiments have been made across St. George’s Channel, between points near Dublin and Holyhead, and always with results entirely incompatible with the doctrine of rotundity.