magnify or enlarge the angle constituting it; when the experiment would appear to fail. But the failure would only be apparent, for a telescope of sufficient power to magnify at the horizon or vanishing point would certainly restore the hull at the greater distance. [3] “Wonders of Science,” by Mayhew, p. 357. [Illustration: FIG. 19.] An illustration or proof of the Earth’s rotundity is also supposed to be found in the fact that navigators by sailing due east or west return in the opposite direction. Here, again, a supposition is involved, viz., that upon a globe _only_ could this occur. But it is easy to prove that it could take place as perfectly upon a circular plane as upon a sphere. Let it first be clearly understood what is really meant by sailing _due east and west_. Practically it is sailing at right angles to north and south: this is determined ordinarily by the mariners’ compass, but more accurately by the meridian lines which converge to the northern centre of the Earth. Bearing this in mind, let N in Figure 19 represent the northern centre; and the lines N. S. the directions north and south. Then let the small arrow, Figure 1, represent a vessel on the meridian of Greenwich, with its head W. at right angles, or due west; and the stern E due east. It is evident that in passing to the position of the arrow, Figure 2, which is still due west or square to the meridian, the arc 1.2 must be described; and in sailing still farther under the same condition, the arcs 2.3, 3.4, and 4.1 will be successively passed over until the meridian of Greenwich, Figure 1, is arrived at, which was the point of departure. Thus a mariner, by keeping the head of his vessel due west, or at right angles to the north and south, practically circumnavigates a plane surface; or, in other words, he describes a circle _upon a plane_, at a greater or lesser distance from the centre N, and being at all times square to the radii north and south, he is _compelled_ to do so--_because_ the earth is a plane, having a central region, towards which the compass and the meridian lines which guide him, converge. So far, then, from the fact of a vessel sailing due west coming home from the east, and _vice versa_, being a proof of the earth’s rotundity, it is simply a phenomenon, consistent with and dependent upon its being a plane! The subject may be perfectly illustrated by the following simple experiment:--Take a round table, fix a pin in the centre; to this attach a thread, and extend it to the edge. Call the centre the north and the circumference the south; then, at any distance between the centre and the circumference, a direction at right angles to the thread will be due east and west; and a small object, as a pencil, placed across or square to the thread, to represent a ship, may be carried completely round the table without its right-angled position being altered; or, the right-angled position firmly maintained, the