FIG. 99.
THE planets are sometimes seen to move from east to west, sometimes from west to east, and sometimes to appear stationary, and it is contended that "the hypothesis of the earth's motion is the natural and easy explanation; and that it would be in vain to seek it from any other system." To those who have adopted the Newtonian theory the above language is quite natural; but when the very foundation of that system is proved to be erroneous, we must seek for the cause as it really exists in the heavens, regardless of every hypothesis and consequence. Careful observation has shown that the advance, apparent rest, and retrogradation of a planet is a simple mechanical result. All the orbits are above the earth; and whenever a spectator stands in such a position that a planet is moving from right to left, he has only to wait until it reaches the end or part of its orbit nearest to him, when, as it turns to traverse the other side of the orbit, it will, for a time, pass in a direction to which the line of sight is a tangent. A good illustration will be found in an elliptical or circular race-course. A person standing at some distance outside the course would see the horses come in from the right, and pass before him to the left; but on arriving at the extreme arc they would for a time pass in the direction of, or parallel to, his line of sight, and would, therefore, appear for a time not to progress, but on entering the other side of the course would appear to the spectator to move from. left to right, or in a contrary direction to that in which they first passed before him. The following diagram, fig. 99, will illustrate this.
Let S be the place of the spectator. It is evident that a body passing from A to P, would pass him from right to left; but during its passage from P to T it would seem not to move across the field of view. On arriving, however, at T, and passing on to B, it would be seen moving from left to right; but from B to A it would again appear to be almost stationary.