LETTER LVII. Attraction-Repulsion-Astrology. MY ESTEEMED Children, In explanation of the last paragraph of my last letter, it is proper to state that, in assigning causes to phenomena, especially where the causes are unseen, people differ as much as they do about forms of religion, government, and many other subjects. Of course it is not my duty or business to perplex you with controversies, but I have given those solutions which satisfy my judgment, and the authority of names ought to have no weight in opposi tion to reason or truth. I have remarked on the terms attraction, and gravity, and heat, which are only proper when used as the mere names of phenomena. They are, however, too often treated as causes, and as inherent, not accidental, phenomena of matter; and the use of them leads to false analogies, or comparisons. Thus also philosophers use the term repulsion, and they allege that bodies and atoms, not only draw or attract, but repel or push one another, by attracting and repelling qualities. But this idea of repulsion is as absurd as that of attraction; for bodies move only in the direction in which they are acted upon, and when two bodies are said to repel one another, both move in the opposite direction; both therefore have their force in the opposite direction, consequently neither can have its own motion in one direction, and its force in the opposite direction. Perhaps even thus far, I give you a specimen of more controversy than you will be amused with; but as these ideas of attraction and repulsion run through all chemistry, and natural philosophy, and one author copies them from another in order to be popular, it is worth while to notice their absurdity, for I should be ashamed to inculcate absurdities for the sake of gratifying any one. Those notions are, however, as old as the Egyp tians, Chaldeans, Greeks, and Romans, and they obtained ready faith in the dark ages, when witchcraft and astrology were fashionable studies; and they were subsequently adopted by more enlightened, but not sufficiently enlightened men. It now appears that all phenomena may be explained by divers motions transferred eternally as their sufficient cause: but our great Newton himself, considered motion itself not a cause, but as produced he says "by certain active principles, such as is that which we call attraction of gravity, and that which causes fermentation, and the cohesion of bodies." So that the cause is here put for the effect, and hence the difficulty of reconciling philosophy with common sense. Apropos, however, of that science of astrology or fortune-telling, of which so many females are to this day constant dupes. It would certainly be very pleasant to know what is to happen, if such knowledge be attainable; but the means having no connexion, either with the parties or the events, the assumption is to the last degree absurd. Something which affords numerous casual combinations is adopted, as the moving planets and heavens, packs of cards, sediments of tea cups, the lines in the hand, dreams, moles, &c. and then by these a hundred probable events are foretold. But if you consider. that a certain proportion of probable events must always happen, as 1 in 2 or 3, so the half or third may happen, whether foretold by those ridiculous means, or guessed at in mere diversion. This, however, is the whole mystery of the imposture of fortune-telling. Yet how many thousands are made uncomfortable by this folly of the human mind. Some half dozen of a hundred things, all which had certain degrees of probability, come to pass, and it is thence believed that all the rest must follow, though the whole were mere probabilities, indicated by things which had no connexion whatever, either with the person or the events. LETTER LVIII. The Earth is a Planet. MY ESTEEMED Children, Let us now consider the mass of the Globe, of which we are part of the inhabitants. To conceive truly of it, we must look through a telescope at Venus or Mars, which it most resembles in size, or at Jupiter, though that planet is equal to a thousand earths. To us, as part of the animalculæ upon its surface, how vast every thing appears upon it, for we measure every thing in relation to ourselves, and feel every thing in relation to our powers and senses. Nevertheless, the sight of those planets, at such distances, corrects some of our false estimates. The globe in round numbers is 8000 miles in diameter, flattened about a 230th part at the poles, and about 25,000 miles round. Its circumference divided into 360 degrees, or parts, gives for each degree about 691⁄2 miles. As it turns completely round in 24 hours, so in every hour 15 degrees turn, and consequently, every 15 degrees, east or west, gives an hour of time, earlier or later. And as there is 60 minutes in an hour, so every degree of longitude is equal to 4 minutes of time. This globe, independent of the elements with which we are acquainted, exhibits to us a great antiquity; accidents of inconceivable extent and force; a succession of productions from the most simple to the present complicated races; the ruins of former conditions and threatened future changes. We know, indeed, only the surface. The rind of the earth alone has been penetrated; the greatest caverns, the deepest mines, do not descend above the sixteenth thousandth part of its diameter. Our judgment, therefore, is confined to the upper stratum. In this coat we find animals, vegetables, minerals, and common material substances. But how little is the information which they can give us concerning the internal mass of the earth! The contemplation of this upper surface is to the component substance of the whole, as the scales of fishes, the feathers of a bird, the epidermis of a man would be in relation to the bones and muscles, the veins and arteries, the circulation of the blood, and the several secretions of the animal economy. Thus, then, we see to what an infinitely greater extent the mind can range into causation and into the universe, than it can into the sphere on which we are placed. Boundless space we may endeavour to force open to our examination. Suns, worlds, planetary existence, it may strive to draw within its grasp, while its efforts on its own soil are confined to the scanty limits of four miles of elevation above the surface, and not even in the ocean itself, of probably more than two miles beneath the general level of the waters. But what is it which fills up the tremendous space that lies hid between pole and pole, and the still more extended equatorial mass? From the properties of a film, (and can we give it any more appropriate term) shall we presume to judge and determine on the form and texture of the internal and central parts? In the eye of analogy, is there any thing which can lead us to suppose the centre to be either positively solid, positively fluid, or rock or metal? The assertion of either one or the other would be extravagant. But system maker-take your globe, elevate your mountains, sink your caverns, excavate your oceans-what now are these to the comparative proportion of the whole sphere? Not more than, to our common optics, is the down on the feather of a moth's wing, or the impression of the bee on the bell of the woodbine. From every appearance, indeed, we have reason to conclude, that the surface of our globe is not only at present upheld by shattered and hollow domes, but that our very towns and cities have their foundation in ruins. Imagination here needs not to be appealed to. We have proof in the records of disastrous history. "In one night," says Pliny, "twelve cities of Asia were struck down by a concussion of the earth." "An earthquake in Peru," says Fournier, "stretched three hundred leagues along the sea shore, and seventy leagues inland: it levelled the mountains as it went, threw down the towns, turned the rivers out of their channels, and made an universal havock and confusion. What vaults and caverns under such a continent! what monstrous chasms, which could receive a fractured and sinking country for nine hundred miles in extent." Notwithstanding this frightful picture, we yet reside upon these awful ruins, in perfect content and security. On a cursory view it must be perceived that the surface of our earth exhibits no great regularity or order. In its outward appearance, it presents us with heights, depths, plains, seas, marshes, rivers, caverns, gulfs, volcanos, and a vast variety of other discordant objects; in its inner, with metals, minerals, stones, bitumens, sands, earths, waters, and matter of every kind, seemingly placed by accident. Yet all these apparent deformities are absolutely necessary to vegetation and animal existence. Were the earth's surface smooth and regular, we should not have those beautiful hills which furnish water. A dreary ocean would cover the globe, which would in such case be suited only for the habitation of fishes. As it is, the motions of the sea and the currents of the air are regulated by the fixed laws. The returns of the season are uniform, and the rigour of winter invariably gives place to the verdure |