Chapter III: Section 2: The Earth No Axial or Orbital Motion

If a ball be allowed to drop from the mast-head of a ship _at rest_, it will strike the deck at the foot of the mast. If the same experiment be tried with a ship _in motion_, the same result will be observed. Because, in the latter case, the ball is acted upon simultaneously by two forces at right angles to each other--one, the momentum given to it by the moving ship in the direction of its own motion, and the other the force of gravity, the direction of which is square to that of the momentum. The ball being acted upon by the two forces together will not go in the direction of either, but will take a diagonal course, as shown in the following diagram, Figure 22.

The ball passing from A to C by the force of gravity, and having at the moment of its liberation received a momentum from the ship in the direction A B, will by the conjoint action of the two forces, take the direction A D, falling at D, just as it would have fallen at C had the vessel remained at rest. In this way, it is contended by those who hold that the Earth is a moving sphere, a ball allowed to fall from the mouth of a deep mine reaches the bottom in an apparently vertical direction, the same as it would if the Earth were motionless. So far, there need be no discussion--the explanation is granted. But now let the experiment be modified in the following way:--Let the ball be thrown _upwards from_ the mast-head of a moving vessel; it will partake as before of two motions, the upward and the horizontal, and will take a diagonal course upwards and with the vessel until the two forces expend themselves, when it will begin to fall by the force of gravity only, and drop into the water far behind the ship, which is still moving horizontally. Diagram Figure 23 will illustrate this effect. The ball being thrown upwards in the direction A C, and the vessel moving from A to B, will cause it to pass in the direction A D, arriving at D when the vessel reaches B; the two forces having expended themselves when the ball arrives at D, it will begin to descend by the force of gravity in the direction D B H, but during its fall the vessel will have reached the position S, so that the ball will drop far behind it at the point H. To bring the ball from D to S _two forces_ would be required, as D H and D W; but as D W does not exist, the force of gravity operates _alone_, and the ball necessarily falls behind the vessel at a distance proportionate to the altitude attained at D, and the time occupied in falling from D to H.

The same result will be observed on throwing a ball directly upwards from a railway carriage when in rapid motion, as shown in the following Figure 24. While the carriage or tender passes from A to B, the ball thrown from A to C will reach the position D, but while the ball then comes down by the force of gravity, _operating alone_, to the point H, the carriage will have advanced to W, so that the ball will always drop more or less behind the carriage, according to the force first given to it in the direction A C and the time occupied in ascending to D, and thence descending to H. It is therefore demanded that if the Earth had a motion upon axes from west to east, and a ball, instead of being dropped down a mine or allowed to fall from the mast head of a ship, be _shot upwards_ into the air; from the moment of its beginning to descend the surface of the Earth would turn from under its direction, and it would fall behind or to the west of its line of descent. On making the experiment _no such effect is observed_, and therefore the conclusion is unavoidable, that the Earth DOES NOT MOVE UPON AXES!

The following experiment has been tried, with the object of obtaining definite results. If the Earth is a globe, having a circumference of 25,000 miles at the equator, the circumference at the latitude of London (51°) will be about 16,000 statute miles; so that the motion of the Earth’s surface, if 25,000 miles in 24 hours at the equator, in England would be more than 700 feet per second. An air-gun was firmly fixed to a strong post, as shown at A in Figure 25, and carefully adjusted by a plumb-line, so that it was perfectly vertical. On discharging the gun, the ball ascended in the direction A C, and invariably (during several trials) descended within a few inches of the gun at A; twice it fell back upon the very mouth of the barrel. The average time that the ball was in the atmosphere was 16 seconds; and, as half the time would be required for the ascent and half for the descent, it is evident that if the Earth had a motion once round its axis in 24 hours, the ball would have passed in 8 seconds to the point D, while the air-gun would have reached the position B H. The ball then commencing its descent, requiring also 8 seconds, would in that time have fallen to the point H, while the Earth and the gun would have advanced as far as W. The time occupied being 8 seconds, and the Earth’s velocity being 700 feet per second, the progress of the Earth and the air-gun to W, in advance of the ball at H, would be 5,600 feet! In other words, in these experiments, the ball, which always fell back to the place of its detachment, should have fallen 5,600 feet, or considerably more than one statute mile to the west of the air-gun! Proving beyond all doubt that the supposed axial motion of the Earth DOES NOT EXIST!

The same experiment ought to suffice as evidence against the assumed motion of the Earth in an orbit; for it is difficult, if not impossible, to understand how the behaviour of the ball thrown from a vertical air-gun should be other in relation to the Earth’s forward motion in space than it is in regard to its motion upon axes. Besides, if it is proved _not_ to move upon axes, the assumption that it moves in an orbit round the Sun is useless for theoretical purposes, and there is no necessity for either denying or in any way giving it farther consideration. But that no point may be taken without direct evidence, let the following experiment be tried:--Take two carefully-bored iron tubes, about two yards in length, and place them, one yard asunder, on the opposite sides of a wooden frame, or a solid block of wood or masonry; so adjust them that their axes of vision shall be perfectly parallel to each other, and direct them to the plane of some notable fixed star, a few seconds previous to its meridian time. Let an observer be stationed at each tube; and the moment the star appears in the first tube, let a knock or other signal be given, to be repeated by the observer at the second tube when he first sees the star. A distinct period of time will elapse between the signals given, showing that the same star is not visible at the same moment by two lines of sight parallel to each other and only one yard asunder. A slight inclination of the second tube towards the first would be required for the star to be seen at the same moment. If now the tubes be left in their position for six months, the same star will be visible at the same meridian time, without the slightest alteration being required in the direction of the tubes. From which result it is concluded that if the Earth had moved _a single yard_ in an orbit through space there would at least be the difference of time indicated by the signals, and the slight inclination of the tube which the difference in position of one yard required. But as no such difference in the direction of the tube is required, the conclusion is unavoidable that in six months a given meridian upon the Earth has not moved a single yard, and that therefore the Earth has not the slightest degree of orbital motion--or motion at right angles to the meridian of a given star! It will be useless to say in explanation that the stars are so infinitely distant that a difference in the angle of inclination of the tube in six months could not be expected, as it will be proved in a subsequent section that _all_ the stars are within a few thousand miles from the Earth’s surface!