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time, equator, measurement, diameter, miles and degree

DEGREES, Measurement of. After New ton had taught that the earth, on account of its motion round its axis, must be highest near the equator, and that the diameter of the equator must be longer, by one 230th part, than the diameter pole to pole, the French wished to investigate the subject further by actual measurement. The measurement was begun with the result that the axis of the poles was found to be longer than a diameter of the equator, and that the earth was, in form, more like a lemon than an orange. For 40 years disputes were maintained on this point without settling the question; and at last the Academy of Sciences resolved, on the proposi tion of Condamine, to have a degree measured at the equator (the expedition went to South America in 1735), and one in Lapland (Kittis and Tornea being the extreme stations to which the expedition was sent in 1736). It was found that the northern degree was greater than that under the equator, and that Newton's conjecture was right. But the question still remained, How great is The flattening of our planet? The iheory said one 230th part; if the earth had been in a perfectly liquid state when it began its rotation. The calculations, however, always gave differ ent results, varying according to the different measurements adopted as the basis of them; for measurements had been made, not only in America and Lapland, but also in France, Eng pole. Under the equator a degree of longitude contains 60 geographical,. 69.16 statute miles. If the form of the earth is not entirely regular, the degrees of longitude on the same parallel of latitude cannot all be of the same length; and it has been proposed to investigate this by actual measurement. This task is in the trigonometric part, as easy as the measurement of a degree of latitude; but in the astronomical part it is 15 times more difficult. The difference of the longitude of two places is determined by the difference of the hour of the day at the same point of time in the two; as a place situated 15 degrees to the east of another has noon a whole hour earlier. One hour, therefore, corresponds

to 15 degrees, or 1,0421/4 statute miles, under the equator, or feet; a minute of time to 91,740 feet, and a second of time to 1,529 feet. A mistake of a second of time, therefore, in calculating the longitude of two places, makes a corresponding error in space. To determine time within two or three seconds, by means of rockets, at a distance of 1,0421/4 miles is im possible; and while the measurement of an arc corresponding to this distance trigonometrically, may be attended with an error to the amount of 200 feet, an astronomical measurement would leave an uncertainty of 2,000 feet. The earlier measurements of the French were directed, in the north, by Maupertuis; in the south by Bouguer. Since that time measurements have been made in all the great continents of the globe—in Pennsylvania, in the time of Maske lyne, by Mason and Dixon; at the Cape of Good Hope by Lacaille, completed by Maclear; in Prussia by Bessel; in Russia by Struve; in Denmark by Schumacher; and in England by Roy Kater and Colby. The French arc from Formentara to Dunkirk was measured by Me chain and Delamore. The results of the meas urements, as given by Airy, make the equatorial diameter 7925.648, and the polar diameter 7899.170 miles. Bessel's results are almost identical namely, equatorial diameter 7925.604 and polar diameter 7899.114 miles. There is an international association, having as its main object the correlation of -all degree measure ments and connected data with the view of accurately ascertaining the figure of the earth.