CHAP. VIII. ABOUT THE INFLUENCES OF THE MOON UPON THE EARTH, AND OF THE EARTH UPON THE MOON. ABOUT THE INFLUENCE OF THE MASS OF THE MOON. ABOUT Tides. ALL the bodies composing the universe exercise influences over each other. The earth influences the moon; the moon influences the earth. The moon is a body, and it is a luminous body; and it appears to exercise influences both as a body and as a light. As a body, that is, as a mass, it exercises the influence of attraction or gravitation; and of this influence of the moon's attraction, a conspicuous effect is generally thought to be the production of the tides of the ocean, from which proceed the tides of the rivers of which the mouths are open to the ocean. There are other opinions of the cause of the tides; but this is what is taught by Newton, and is in the following manner explained. In the diagram which I here show you, M represents the moon, o the earth, z n, the highest parts of the water caused by the moon's attraction. Now let it be observed, that the power of gravity diminishes as the square of the distance increases; and therefore the waters at z, on the side of the earth A B C D E F G H a, next the moon м, are more attracted than the central parts of the earth o by the moon, and the central parts are more attracted by her than the waters on the opposite side of the earth at n; and therefore the distance between the earth's centre and the waters on its surface, under the opposite to the moon, will be increased. For let there be three bodies at H, O, and D: if they are all equally attracted by the body м, they will all move equally fast towards it, their mutual distances from each other continuing the same. If the attraction of n is unequal, then that body which is most strongly attracted will move fastest, and this will increase its distance from the other body. Therefore, by the law of gravitation, м will attract H more strongly than it does o, by which the distance between H and o will be increased; and a spectator at o will perceive H rising higher towards z. In like manner, o being more strongly attracted than D, it will move farther towards м than D does; consequently, the distance between o and D will be increased; and a spectator at o, not perceiving his own motion, will see D receding from him towards n; all effects and appearances being the same, whether D recedes from o, or o from D. According to later philosophers, however, the tides are produced by the combined influences of the moon and the sun; and even still present an astronomical problem the most difficult of solution, and hitherto the least satisfactorily disposed of. Great exertions are at present in the progress of being made, to obtain, by means of continual observation in a variety of places throughout the world, and by the most careful registration of facts, a more complete account of the tides, tending to the discovery of all their causes, than any that is yet possessed. CHAP. IX. ABOUT THE INFLUENCES OF THE LIGHT OF THE MOON. ABOUT THE WEATHER. ABOUT THE CHANGES OF THE MOON. ABOUT OLD MOONS AND YOUNG MOONS. ABOUT NEW MOONS, FULL MOONS, HALF MOONS, AND THREEQUARTER MOONS. THE SAILOR'S VOYAGE TO THE END OF THE WORLD, AND HIS DISCOVERY OF THE HEAPS OF THE OLD MOONS. If the question of the influence of the moon in respect of the tides is still open to examination, much more so is that of the influence of the moon upon the weather. The ancient and general persuasion is, that changes of the weather follow changes of the moon. The proof must depend upon accurate observation; but there are difficulties even in the way of the theory, if we strictly consider the real history and nature of the moon. I shall leave it to my little readers to form a better judgment of the whole matter hereafter, |