Tortato, bishop of Avila, near the close of the fifteenth century, declares in his commentary on Genesis, that the Christian faith is shaken, if the earth is believed to be round. Columbus, Vespucius, and Magellan, not having the fear of excommunication by this learned bishop before their eyes, the earth resumed its rotundity in spite of him. Then man went from one extreme to the other, and the earth was regarded as a perfect sphere. But the error of the perfect sphere was the mistake of philosophers, while that of a long, flat earth was the blunder of idiots. When once it began to be clearly known that our globe revolves on its own axis every twenty-four hours, it might have been inferred from that alone that its form could not be absolutely round. Not only does the centrifugal zone considerably raise the waters in the region of the equator, by the motion of the diurnal rotation, but they are moreover elevated about twenty-five feet, twice a day, by the tides; the lands about the equator must then be perfectly inundated. But they are not so; therefore the region of the equator is much more elevated, in proportion, than the rest of the earth: then the earth is a spheroid elevated at the equator, and cannot be a perfect sphere. This proof, simple as it is, had escaped the greatest geniuses: because a universal prejudice rarely permits investigation. We know that, in 1762, in a voyage to Cayenne, near the line, undertaken by order of Louis XIV., under the auspices of Colbert, the patron of all the arts, Richer, among many other observations, found that the oscillations or vibrations of his timepiece did not continue so frequent as in the latitude of Paris, and that it was absolutely necessary to shorten the pendulum one line and something more than a quarter. Physics and geometry were at that time not nearly so much cultivated as they now are; what man would have believed that an observation so trivial in appearance, a line more or less, could lead to the knowledge of the greatest physical truths? It was first of all discovered that the weight must necessarily be less on the equator than in our latitudes, since weight alone causes the oscillation of a pendulum. Consequently, the weight of bodies being the less the farther they are from the centre of the earth, it was inferred that the region of the equator must be much more elevated than our own--much more remote from the centre; so the earth could not be an exact sphere.