CHAPTER VIII.
THE FRENCH PHILOSOPHERS.
After so many abortive attempts to reach the Golden Empire, the ardor of research greatly abated. No expeditions, composed of considerable numbers, have since embarked in the enterprise; but from time to time, for the century succeeding Raleigh's last attempt, private expeditions were undertaken and encouraged by provincial governors; and several hundred persons perished miserably in those fruitless endeavors.
The adventure we are now about to record was of an entirely different character in respect to its objects and the means employed; but it occupied the same field of action, and called into exercise the same qualities of courage and endurance.
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. The degrees of least curvature will be longest, and those of greatest curvature shortest; that is, one would have to travel farther on the flattened part of the earth to see any difference in the position of the north-star than in those parts where the curvature is greater. So a degree of latitude near the pole, if determined by the position of the north-star, would be found, by actual measurement, to be longer than one similarly determined at the equator. It was to ascertain whether the fact was so that the two scientific expeditions were sent out.
The party which was sent to the northern regions travelled over snow and ice, swamps and morasses, to the arctic circle, and fixed their station at Tornea, in Lapland. The frozen surface of the river afforded them a convenient level for fixing what is called by surveyors the base line. The cold was so intense, that the glass froze to the mouth when they drank, and the metallic measuring rod to the hand. In spite, however, of perils and discomforts, they persevered in their task, and brought back careful measurements of a degree in latitude 66° north, to be compared with those made by the other party at the equator, whose movements we propose more particularly to follow.
Before we take leave of the northern commissioners, however, we will mention another method they took of demonstrating the same fact. If the earth be depressed at the poles, it must follow that bodies will weigh heavier there, because they are nearer the centre of the earth. But how could they test this fact, when all weights would be increased alike,—the pound of feathers and the pound of lead? The question was settled by observing the oscillation of a pendulum. The observers near the pole found that the pendulum vibrated faster than usual, because, being nearer the centre of the earth, the attracting power was increased. To balance this, they had to lengthen the pendulum; and the extent to which they had to do this measured the difference between the earth's diameter at the poles, and that in the latitude from which they came.
The commissioners who were sent to the equatorial regions were Messrs. Bouguer, La Condamine, and Godin, the last of whom was accompanied by his wife. Two Spanish officers, Messrs. Juan and De Ulloa, joined the commission. The party arrived at Quito in June, 1736, about two hundred years after Gonzalo Pizarro started from the same place in his search for Eldorado. In the interval, the country had become nominally Christian. The city was the seat of a bishopric, an audience royal, and other courts of justice; contained many churches and convents, and two colleges. But the population was almost entirely composed of Indians, who lived in a manner but very little different from that of their ancestors at the time of the conquest. Cuença was the place next in importance to the capital; and there, or in its neighborhood, the chief labors of the commission were transacted. They were conducted under difficulties as great as those of their colleagues in the frozen regions of the north, but of a different sort. The inhabitants of the country were jealous of the French commissioners, and supposed them to be either heretics or sorcerers, and to have come in search of gold-mines. Even persons connected with the administration employed themselves in stirring up the minds of the people, till at last, in a riotous assemblage at a bullfight, the surgeon of the French commissioners was killed. After tedious and troublesome legal proceedings, the perpetrators were let off with a nominal punishment. Notwithstanding every difficulty, the commissioners completed their work in a satisfactory manner, spending in all eight years in the task, including the voyages out and home.