A very striking illustration of the true form of the sea horizon may be observed from the high land in the neighbourhood of the head of Portsmouth Harbour. Looking across Spithead to the Isle of Wight, the base or margin of the island, where water and land come together, appears to be a straight line from east to west, a length of twenty-two statute miles. If a good
theodolite is directed upon it, the cross-hair will show that the. land and water line is perfectly horizontal, as shown in fig. 19.
If the earth is globular, the two ends east and west of the Isle of Wight would be 80 feet below the centre, and would appear in the field of view of the theodolite as represented in fig. 20. As a proof that such would be the appearance, the same instrument directed upon any object having an upper outline curved in the smallest degree, will detect and plainly show the curvature in relation to the cross-hair a b; or the levelled board employed in experiment 7, fig. 18, will prove the same condition to exist; viz., that the margin of the Isle of Wight is, for twenty-two miles, a perfectly straight line; and instead of curvating downwards 80 feet each way from the centre, as it certainly would if convexity existed, it is absolutely horizontal.
From the lighthouse on Bidstone Hill, near Liverpool, the. whole length of the Isle of Man, on a clear day and with a good telescope, is distinctly visible, and presents the same horizontal base line as that observed in the Isle of Wight.
From the high land near Douglas harbour, Isle of Man, the whole length of the coast of North Wales is often plainly visible to the naked eye--a distance extending from the point of Ayr, at the mouth of the River Dee, towards Holyhead, not
less than fifty miles. Whatever test has been employed, the line, where the sea and the land appear to join, is always found to be perfectly horizontal, as shown in the following diagram; fig. 21.
whereas, if the earth is spherical, and therefore the surface of all water convex, such an appearance could not exist. It would of necessity appear as shown in fig. 22.
A line stretched horizontally before the observer would not only show the various elevations of the land, but would also show the declination of the horizon H, H, below the cross-line S, S. The fifty miles length of the Welsh coast seen along the horizon in Liverpool Bay, would have a declination from the centre of at least 416 feet (252 x .8 inches = 416 feet 8 inches). But as such declination, or downward curvation, cannot be detected, the conclusion is logically inevitable that it has no existence. Let the reader seriously ask whether any and what reason exists in Nature to prevent the fall of more than 400 feet being visible to the eye, or incapable of detection by any optical or mathematical means whatever. This question is especially important when it is considered that at the same distance, and on the upper outline of the same land, changes of level of only a few yards extent are quickly and unmistakably perceptible.
[paragraph continues] If he is guided by evidence and reason, and influenced by a love of truth and consistency, he cannot longer maintain that the earth is a globe. He must feel that to do so is to war with the evidence of his senses, to deny that any importance attaches to fact and experiment, to ignore entirely the value of logical process, and to cease to rely upon practical induction.
