SHAPE AND SIZE OF THE EARTH. MEASURING degree

Reasonably can be argued that in both cases, the data of the Alexandrian scholar were simply translated into modern measures. The new era in the history of the issue begins work Dutchman Snell, who in 1615 first made the trigonometric definition terrestrial arc between Bergen and Alkmarom in the Netherlands and applied for this method having wide circulation in the present. The essence of it are as follows: measured arbitrarily taken the main line, and if the ends of her sighting some distant point, we get a triangle in which the known side and two angles, according to these data it is easy to calculate unknown sides and thus obtain three lines of known value, and if from the last sighting again some new points, and calculating the obtained triangles, repeating the same manipulation, we can cover the whole area a network of triangles and determine, finally, the distance between those points that have been selected to measure the degree. To check the calculations can be directly measured one of the sides of triangles. This technique is very simple in theory but its application meets a number of difficulties, irregular shape of the earth's surface, the effect of temperature on the measuring devices and a host of other conditions interfere with the accuracy of measurements, all these sources of error must be provided and corrected. In measurements of degrees produced in Spain, the base was equal to 14x / 2 miles, the error is not reached, and 3 mm, hence it is clear that the degree of measurement in the modern requirements of science are among the most difficult problems of natural science, which can be performed only for large vehicles. Snell's method was refined by the French, who first came to him through the results of paramount importance. Were of great importance Picard measurements made in 1669 - 1670 years. between Amen and Malvuazinoy: later French triangulation network has expanded significantly and has covered all the space from Dyunkirhena on the Strait of Pas-de-Calais to the Mediterranean Sea. For all degree measurements initially assumed that the Earth is quite correct ball, but soon, this assumption proved incorrect. It was observed that the pendulum clock, are made in our latitudes, its magnitude is equal to second, behind the equator, and to report them to the proper course should be somewhat shortened pendulum. To investigate this fact, the French Academy sent an expedition to Cayenne with Richer (Richer), headed, the latter found that the velocity of the pendulum swings seconds remains unchanged when its length will be reduced by 13 / 4 lines. Pendulum oscillations are due to gravity, and if in some areas the movement slows down, it shows that here the value of gravity lower than elsewhere in the earth's surface. Earth's magnetic force weakens with distance from the center, which implies that the Earth is not the proper sphere: it stretched from the equator, flattened at the poles and has a form of so-called ellipsoid of revolution, ie, like an orange. The same conclusion was reached by Newton and Huygens, a purely theoretical way, assuming that the Earth was originally located in a liquid or, at least in a plastic state. Revolving around the axis, it is under the influence of centrifugal force took the form of an ellipsoid of revolution. If the Earth really did not have this form, the water would have to assemble at the equator and pour over the continents: on the contrary, the polar countries would be completely deprived of the seas. Measurement of degrees produced so far have had no meaning to address this issue. If the Earth is flattened at the poles, then the degrees of the meridian should become shorter as they approach the equator; French measurements showed even the opposite: it was found that in the southern part of the country's degree meridian is somewhat longer than in the north. This forced the French astronomer Cassini make vigorous opponent of Newton and Huygens, he argued that the Earth at the equator and flattened at the poles stretched out, ie, like a lemon. But the measurement methods at the time were too far from perfect, and to determine accurately the differences in the value of degrees as close to places like North and South France, is very difficult. To resolve the dispute the French Academy has found it necessary to measure the meridian in two significantly remote areas - one at the equator in Peru, the other - in the Far North, in Lapland. Bouguer and Condamine went for that purpose in 1735 in Quito, and Maupertuis and Clairaut in 1736 in Lapland. Here they made their famous works, which, though not meet modern requirements, but at that time had very significant results, and undoubtedly proved that the Earth is flattened at the poles. Degree meridian in Lapland, was equal to 57.437 fathoms, and in Peru 56.753 (toise = 6 Paris feet). More successful were the measurement of degrees produced in France again. In 1790 the National Assembly decided to introduce a new natural system of measures. For the basic unit took part sorokamillionnuyu meridian and called it the meter. We now know that the meter in the form in which he was then defined, does not reproduce exactly this value. Trying to create a new natural system of measures was unsuccessful, but measurements degrees between Dyunkirhenom and Bartselonoy made for the purpose of improving the way, were of great importance to science.