In 1735, the French Academy of Science made arrangements for sending out two commissions of learned men to different and distant parts of the world to make measurements, with a view to determining the dimensions and figure of the earth. The great astronomer, Sir Isaac Newton, had deduced from theory, and ventured to maintain, that the earth was not a perfect globe, but a spheroid; that is, a globe flattened at the poles. For a long time after Newton's splendid discoveries in astronomy, a degree of national jealousy prevented the French philosophers from accepting his conclusions; and they were not displeased to find, when they could, facts opposed to them. Now, there were some supposed facts which were incompatible with this idea of Newton's, that the earth was flattened at the poles. The point was capable of being demonstrated by measurements, with instruments, on the surface; for, if his theory was true, a degree of latitude would be longer in the northern parts of the globe than in the regions about the equator. We must not allow our story to become a scientific essay; and yet we should like to give our readers, if we could, some idea of the principle on which this process, which is called the measurement of an arc of the meridian, was expected to show the magnitude and form of the earth. We all know that geographical latitude means the position of places north or south of the equator, and is determined by reference to the north or pole star. A person south of the equator would not see the pole-star at all. One at the equator, looking at the pole-star, would see it, if no intervening object prevented, in the horizon. Advancing northward, he would see it apparently rise, and advance toward him. As he proceeded, it would continue to rise. When he had traversed half the distance to the pole, he would see the pole-star about as we see it in Boston; that is, nearly midway between the horizon and the zenith: and, when he had reached the pole, he would see the pole-star directly over his head. Dividing the quarter circle which the star has moved through into ninety parts, we say, when the star has ascended one-ninetieth part, that the observer has travelled over one degree of latitude. When the observer has reached Boston, he has passed over somewhat more than forty-two degrees, and, when he has reached the north-pole, ninety degrees, of latitude. Thus we measure our latitude over the earth's surface by reference to a circle in the heavens; and, because the portions into which we divide that circle are equal, we infer that the portions of the earth's surface which correspond to them are equal. This would be true if the earth were a perfect globe: but if the earth be a spheroid, as Newton's theory requires it to be, it would _not_ be true; for that portion of the earth's surface which is flattened will have less curvature than that which is not so, and less still than that portion which is protuberant.