It has been shown that a plane can be circumnavigated, and therefore the first or major proposition is false; and, being so, the conclusion is false. This portion of the subject furnishes a striking instance of the necessity of, at all times, proving a proposition by direct and immediate evidence, instead of quoting a natural phenomenon as a proof of what has previously been assumed. But a theory will not admit of this method, and therefore the zetetic process, or inquiry before conclusion, entirely eschewing assumption, is the only course which can lead to simple and unalterable truth. Whoever creates or upholds a theory, adopts a monster which will sooner or later betray and enslave him, or make him ridiculous in the eyes of practical observers.
Closely following the subject of circumnavigation, the gain and loss of time discovered on sailing east and west is referred to as another proof of rotundity. But this illustration is equally fallacious with the last, and from the same cause, viz., the assumption that a globe only could produce the effect observed. It will be seen, by reference to diagram, [Figure 19], that the effect must take place equally upon a plane as upon a globe. Let the ship, W E, upon the meridian, Figure 1, at 12 at noon, begin to sail towards the position, Figure 2, which it will reach the next day at 12, or in 24 hours: the sun during the same 24 hours will have returned only to Figure 1, and will require to move for another hour or more until it reaches the ship at Figure 2, making 25 hours instead of 24, in which the sun would have returned to the ship, if it had remained at Figure 1. In this way, the sun is more and more behind the meridian time of the ship, as it proceeds day after day upon its westerly course, so that on completing the circumnavigation the ship’s time is a day later than the solar time, reckoning to and from the meridian of Greenwich. But the contrary follows if the ship sails from Figure 1 towards Figure 4, or the east, because it will meet the sun one hour earlier than the 24 hours which would be required for it to pass on to Figure 1. Hence, on completing the circle 1.4.3.2.1, the time at the ship would be one day in advance of the time at Greenwich, or the position Figure 1. Captain Sir J. C. Ross, at page 132, vol. 2, says—“November 25, having by sailing to the eastward gained 12 hours, it became necessary, on crossing the 180th degree and entering upon west longitude, in order to have our time correspond with that of England, to have two days following of the same date, and by this means lose the time we had gained, and still were gaining, as we sailed to the eastward.”
In further illustration of this matter, and to impress the mind of the readers with its importance as an evidence in support of the theory of the earth’s sphericity, several authors have given the following story:—Two brothers, twins, born within a few minutes of each other, and therefore of the same age, on growing to manhood went to sea. They both circumnavigated the earth, but in opposite directions; and when they again met, one was a day older than the other!
Whatever truth there may be in this account, it is here shown to be no more favourable to the idea of rotundity than it is to the opposite fact that the earth is a plane; as both forms will permit of the same effect.
Another phenomenon supposed to prove rotundity, is found in the fact that Polaris, or the north polar star, gradually sinks to the horizon as the mariner approaches the equator, on passing which it becomes invisible. First, it is an ordinary effect of perspective for an object to appear lower and lower as the observer recedes. Let any one try the experiment of looking at a lighthouse, church spire, monument, gas-lamp, or other elevated object, from the distance of a few yards, and notice the angle at which it is observed: on going farther away, the angle will diminish and the object appear lower, until, if the distance be sufficiently great, the line-of-sight to the object, and the apparently ascending surface of the Earth upon which it stands will converge to the angle which constitutes the vanishing point; at a single yard beyond which it will be invisible. This, then, is the necessary result of the everywhere visible law of perspective operating between the eye-line and the plane surface upon which the object stands; and has no relation whatever to rotundity.
It is not denied that a similar depression of a distant object would take place upon a globe; it is simply contended that it would not occur upon a globe exclusively. But if the Earth is a sphere and the pole star hangs over the northern axis, it would be impossible to see it for a single degree beyond the equator, or 90 degrees from the pole. The line-of-sight would become a tangent to the sphere, and consequently several thousand miles out of and divergent from the direction of the pole-star. Many cases, however, are on record of the north polar star being visible far beyond the equator, as far even as the tropic of Capricorn. In the Times newspaper of May 13, 1862, under the head of “Naval and Military Intelligence,” it is stated that Captain Wilkins distinctly saw the Southern Cross and the polar star at midnight in 23·53 degrees of latitude, and longitude 35·46.
FIG. 20.
This would be utterly impossible if the Earth were a globe, as shown in the diagram, [Figure 20]. Let N represent the north pole, E E the equator, C C the tropic of Capricorn, and P the polar star. It will be evident that the line-of-sight C D being a tangent to the Earth beyond the equator E must diverge from the axis N and could not by any known possibility cause the star P to be visible to an observer at C. No matter how distant the star P, the line C D being divergent from the direction N P could never come in contact with it. The fact, then, that the polar star has often been seen from many degrees beyond the equator, is really an important argument against the doctrine of the Earth’s rotundity.
It has been thought that because a pendulum vibrates more rapidly in the northern region than at the equator, the Earth is thereby proved to be a globe; and because the variation in the velocity is not exactly as it should be if all the surface of the Earth were equidistant from the centre, it has been concluded that the Earth is an oblate spheroid, or that its diameter is rather less through the poles than it is through the equator. The difference was calculated by Newton to be the 235th part of the whole diameter; or that the polar was to the equatorial diameter as 689 to 692. Huygens gave the proportion as 577 to 875 or a difference of about one-third of the whole diameter. Others have given still different proportions; but recently the difference of opinion has become so great that many have concluded that the Earth is really instead of oblate an oblong spheroid. It is certain that the question when attempted to be answered by measuring arcs of the meridian, is less satisfactory than was expected. This will be evident from the following quotation from the account of the ordnance survey of Great Britain, which was conducted by the Duke of Richmond, Col. Mudge, General Roy, Mr. Dalby, and others, who measured base lines on Hounslow Heath and Salisbury Plain with glass rods and steel chains: “when these were connected by a chain of triangles and the length computed the result did not differ more than one inch from the actual measurements—a convincing proof of the accuracy with which all the operations had been conducted.