It is the natue of fluids to be and remain level, and when that level is disturbed in any influence whatever, motion ensues until the level is resumed.
Professor Airy tells us, in his “Six Lectures on Astronomy,” that “quick-silver is perfectly fluid, its surface is perfectly horizontal.” We may add that all fluids are the same for the reason given by the next writer.
Mr W. T. Lynn, of the Royal Observatory, Greenwich, in his “First Principles of Natural Philosophy,” says: “the upper surface of a fluid at rest is a horizontal plane. Because if a part of the surface were higher than the rest, those parts of the fluid which were under it would exert a greater pressure upon the surrounding parts than than they receive from them, so that the motion would take place amongst the particles and continue until there were none at a higher level than the rest, that is, until the upper surface of the whole mass of fluid became a horizontal plane.”
The English Mechanic of June, 1896, says:
“Since any given body of water…must have a level surface, i.e., no one part higher than another, and seeing that all our oceans (a few inland seas excepted) are connected together, it follows that they are all virtually of the same level.”
In March, 1870, the bedofor Canal was chosen to experiment upon with a view of determining whether water was horizontal or convex.
The following argument is taken from the report as printed in The Field for 26th March, 1870, and is considered to be sufficient an un-answerable:
“The stations appeared, to all intents and purposes, equidistant in the field of view, and also in regular serise; first, the distant bridge, secondly, the central signal, and, thirdly, the horizontal cross-hair marking the point of observation, showing that the central disc 18 ft. 4 in. high does not depart from a straight line taken from end to end of the six miles in any way whatever, laterally or verticall. For, if no so and (as in the case of the disc 9 ft. 4 in. high) if it were lower or nearer the water, it would appear, as that disc does, nearer to the distant bridge. If it were higher, it would appear in the