From Kepler's Second Law we know that equal areas are described by the radius vector in equal times, and if the first law of Kepler is at all applicable to the sun, then it must follow that if the sun has an orbit, and moreover an elliptic orbit as stated by Kepler himself, then, as a natural result, the radius vector of the sun must move over equal areas in equal times. The physical explanation of Kepler's Second Law was given in Art. 103, and there is no need to traverse the same ground again. It is, therefore, true that the sun moves faster in certain parts of its orbit than in others, being urged through space at its greatest velocity when it is nearest its controlling centre, and slowest when farthest away from that controlling centre. Herschel, in his work on _Astronomy_, states: "The motion of the sun will be such that equal areas are thus swept over by the revolving radius vector in equal times in whatever part of the circumference of the ellipse the sun may be moving." He, however, suggested that the earth forms a focus of the sun's ellipse, a suggestion which is unphilosophical, it seems to me, as we might equally suggest that the earth revolves round the moon, which is contrary to all observation. Thus the sun is not carried uniformly through space by the aetherial currents of its central body, because it is nearer to that central body at certain times; its velocity being regulated by its distance from that body, the same being increased as the distance is decreased, and decreased as the distance increases. Now if this reasoning be correct, and if the sun really moves round a central body and is subject to Kepler's Second Law, then that increase and decrease of distance will be made manifest in the increase and decrease of the eccentricity of the earth's orbit. So that if the eccentricity of the earth's orbit should vary from century to century, then we have conclusive evidence that the sun obeys the first and second of Kepler's Laws, and therefore that it revolves around a controlling centre of its own. From observation we find that this is exactly what is happening, and that at the present time the eccentricity of the earth's orbit is gradually diminishing, and in about 24,000 years the orbit will be very nearly a circle. Now, from what was stated in Art. 106, we know that the moon's orbit will be nearly a circular orbit when the earth is farthest from the sun, and that then its orbital velocity is at a minimum. In order for this result to be produced, the earth must reach that part of its orbit known as aphelion, where the distance from its controlling centre is greatest, so that the eccentricity of the moon's orbit is always an indication of the position of the earth in its relation to the sun. When the eccentricity of the moon's orbit is decreasing, the earth's distance from the sun is increasing, but when the eccentricity of the moon's orbit is increasing, then the earth's distance from the sun is decreasing.