So, ultimately we come down to this:
1. We all agree that water finds its own level, and that water conforms to the shape of the Earth
2. Targets placed parallel to the surface of a body of water will conform to the shape of the surface of the water
3. These same targets, then, will conform to the shape of the earth
4. The Old Bedford River northeast of Welney, between a sluice gate 181m northeast of Welney Bridge and a road bridge just southwest of the Old Bedford Sluice, provides a 5.85-mile perfectly straight stretch of standing water with no obstacles along its length
5. Three targets placed parallel to the surface of the water, at, for example, 0.2, 3, and 5.65 miles will reveal the shape of the surface of the water
6. The targets should be placed high enough to minimise the effects of refraction (for example, at 13 feet above the surface of the river)
7. A telescope or telescopic camera placed at the same height as the targets can be used to view the them
8. Diagrams and scale models predict the following: a) that if the shape of the surface of the water is flat, the three targets will appear to be at the same height as one another; or b) if the shape of the surface of the water is convexly curved, the middle target will appear higher than the other two
9. These two outcomes can only occur with the associated shape: that is, if the shape of the surface of the water is flat, it is impossible for the middle target to appear higher than the other two; and if the shape of the surface of the water is curved, it is impossible for the three targets to appear to be at the same height as one another - regardless of how the elevation or tilt of the camera/observer is altered
10.If the camera is higher than the level of the targets, the following will be observed: a) if the water is flat, the distant target will appear highest, then the middle one, then the near one; or b) if the water is curved, the near target will appear lowest, while the distant target will appear to raise in the frame as the observer raises, until it appears higher than the middle target
11. If the camera is lower than the level of targets, the following will be observed: a) if the water is flat, the near target will appear highest, then the middle one, then the far one; or b) if the water is curved, the distant target will appear lowest, while the near target will appear to raise in the frame as the observer lowers, until it appears higher than the middle target
12. Both the above points are also predicted with diagrams and scale models. Though they are incidental the main point of the experiment
13. Tilting the camera does nothing to alter the apparents heights of the three targets, but merely changes their position, as a group, in the frame
In a nutshell:
1. Three targets and a camera are placed at the same height above a sufficiently long straight body of water
2. Observations are made
3. If the targets all appear to be at the same height, the surface of the river is flat
4. If the middle target appears higher than the near and far target, the surface of the river is curved
Any suggestions for improvements and clarifications?