Carriages similarly receding will seem to lose that portion of the rim of the wheels which touches the Earth; the axles will seem to get lower; and at the distance of a few miles, the body will appear to drag along in contact with the ground. This is very remarkable in the case of a railway carriage when moving away upon a straight and level portion of line several miles in length. These instances, which are but a few of what might be quoted, will be sufficient to prove, beyond the power of doubt or the necessity for controversy, that upon a plane or horizontal surface, the _lowest part_ of bodies receding from a given point of observation will disappear _before the higher_. This is precisely what is observed in the case of a ship at sea, when outward bound--the _lowest_ part--the hull, disappearing before the higher parts--the sails and mast head. Abstractedly, when the lowest part of a receding object thus disappears by entering the “vanishing point,” it could be seen again to any and every extent by a telescope, if the power were sufficient to magnify at the distance observed. This is to a great extent practicable upon smooth horizontal surfaces, as upon frozen lakes or canals; and upon long straight lines of railway. But the power of restoring such objects is greatly modified and diminished where the surface is undulating or otherwise moveable, as in large and level meadows, and pasture lands generally; in the vast prairies and grassy plains of America; and especially so upon the ocean, where the surface is always more or less in an undulating condition. In Holland and other level countries, persons have been seen in winter, skating upon the ice, at distances varying from ten to twenty miles. On some of the straight and “level” lines of railway which cross the prairies of America, the trains have been observed for more than twenty miles; but upon the sea the conditions are altered, and the hull of a receding vessel can only be seen for a few miles, and this will depend very greatly--the altitude of the observer being the same, upon the state of the water. When the surface is calm, the hull may be seen much farther than when it is rough and stormy; but under ordinary circumstances, when to the naked eye the hull has just become invisible, or is doubtfully visible, it may be seen again distinctly by the aid of a powerful telescope. Although abstractedly or mathematically there should be no limit to this power of restoring by a telescope a lost object upon a smooth horizontal surface, upon the sea this limit is soon observed; the water being variable in its degree of agitation, the limit of sight over its surface is equally variable, as shown by the following experiments:--In May, 1864, on several occasions when the water was unusually calm, from the landing stairs of the Victoria pier at Portsmouth, and from an elevation of 2 ft. 8 in. above the water, the greater part of the hull of the Nab Light-ship was, through a good