The matter may be summarized as follows:--At any time when the sea is calm and the weather clear, the Light of the Eddystone, which is 89 feet above the foundation on the rock, may be distinctly seen from an elevation of 5 feet above the water level; according to the Admiralty directions, it “may be seen 13 nautical (or 15 statute) miles,”[41] or one mile still farther away than the position of the observers on the above-named occasion; and yet _on that occasion_, and at a distance of only 14 statute miles, notwithstanding that it was a very fine autumn day, and a clear back ground existed, not only was the lantern, which is 89 feet high, not visible, but the _top of the vane_, which is 100 feet above the foundation was, as stated in the report, “_entirely out of sight_.” [41] “Lighthouses of the World,” p. 36. [Illustration: FIG. 32.] That vessels and lighthouses are sometimes more distinctly seen than at others; and that the lower parts of such objects are sooner lost sight of when the sea is rough than when it is calm, are items in the experience of seafaring people as common as their knowledge of the changes in the weather; and prominence is only given here to the above case because it was verified by persons of different opinions upon the subject of the Earth’s form, and in the presence of several hundreds of the most learned and respectable inhabitants of Plymouth and the neighbourhood. The conclusion which such observations necessitate and force upon us is, that the law of perspective which is everywhere visible on land, is _modified_ when observed in connection with objects upon or near the sea. But _how_ modified? If the water of the ocean were frozen and at perfect rest, any object upon its surface would be seen as far as telescopic or magnifying power could be brought to bear upon it. But because this is not the case--because the water is always more or less in motion, not only of progression but of fluctuation, the swells and waves, into which the surface is broken operate to prevent the line of sight from passing parallel to the horizontal surface of the water. It has been shown at pages 16 to 20, and also at 25 to 33, that the surface of the Earth and Sea appears to rise up to the level, or altitude of the eye; and that at a certain distance the line of sight and the surface which is parallel to it appear to converge to a “vanishing point;” which point is “the horizon.” If this horizon, or vanishing point, were formed by the apparent junction of two _perfectly stationary_ parallel lines, it could be penetrated by a telescope of sufficient power to magnify at the distance; but because upon the sea the surface of the water is _not stationary_, the line of sight at the vanishing point becomes angular instead of parallel, and telescopic power is of little avail in restoring objects beyond this point. The following diagram will render this clear:--The horizontal line C D E and the line of sight A B are parallel to each other, and