The subject of perspective will not be rendered sufficiently clear unless an explanation be given of the cause and character of what is technically called the “vanishing point.” Why do objects, even when raised above the earth, vanish at a given distance? It is known, and can easily be proved by experiment, that “the range of the eye, or diameter of the field of vision is 110°; consequently this is the _largest_ angle under which an object can be seen. The range of vision is from 110° to 1°. * * The _smallest_ angle under which an object can be seen is upon an average for different sights the 60th part of a degree, or _one minute_ in space; so that when an object is removed from the eye 3000 times its own diameter, it will only just be distinguishable; consequently, the greatest distance at which we can behold an object, like a shilling, of an inch in diameter is 3000 inches or 250 feet.”[3] It may, therefore, be very easily understood that a line passing over the hull of a ship, and continuing parallel to the surface of the water, must converge to the vanishing point at the distance of about 3000 times its own elevation; in other words, if the surface of the hull be 10 feet above the water it will vanish at 3,000 times 10 feet; or nearly six statute miles; but if the mast-head be 30 feet above the water, it will be visible for 90,000 feet or over 17 miles; so that it could be seen upon the horizon for a distance of eleven miles _after the hull had entered the vanishing point_! Hence the phenomenon of a receding ship’s hull being the first to disappear, which has been so universally quoted and relied upon as proving the rotundity of the Earth is fairly and logically a proof of the very contrary! It has been misapplied in consequence of an erroneous view of the law of perspective, and the desire to support a theory. That it is valueless for such a purpose has already been shown; and that, even if there were no question of the Earth’s form involved, it could not arise from the convexity of the water, is proved by the following experiment:--Let an observer stand upon the sea-shore with the eye at an elevation of about six feet above the water, and watch a vessel until it is just “hull down.” If now a good telescope be applied the hull will be distinctly _restored to sight_! From which it must be concluded that it had disappeared through the influence of perspective, and not from having sunk behind the summit of a convex surface! Had it done so it would follow that the telescope had either carried the line-of-sight through the mass of water, or over its surface and down the other side! But the power of “looking round a corner” or penetrating a dense and extensive medium has never yet been attributed to such an instrument! If the elevation of the observer be much greater than six feet the distance at which the vanishing point is formed will be so great that the telescope may not have power enough to