The daily morning journal and courier., 1898-07-29

inf cat, the cientists are entertaining the hypothesis that the earth Is grad ually versing toward the tetrahedron-- solid bounded by four triangles, or triangular pyramd-with the apex at the south pole, and the continents rep resenting the bulging out from the spherical surface Of course, the earth is not yet far out of it's spherical form, if the tetrahedral theory be proved, but certain facts make the hypothesis an interesting one. The earth in it's cooling. according to the theory, is causing a collapse of it's envelope, or crust, and while the sphere is that geometrical body whic h has the great est volume for given surface, and the tetrahedron the least, the shrinkage of the interior would tend to throw the superficial envelope, grown too large by the shrinkage of the interior, into tetrahedral form. In October a series of experiments under the direction of the International eodetic Association will be undertaken, and in this country the Coast and Geodetic Survey will have charge of Americas share of the work. From the observations made it will be possible to derive some fresh CT conclusions as to the shape of the kindred subjects.
 Tt is remarkable" said MT. E. D. Preston of the Coast Survey to your correspondent, 'how long the size and figure of the earth have been subject of scientific study. There are several ways of determining the earth's size and shape, but the method adopted by our Coast Survey is to measure arcs on the surface of the earth, and from these we can find the curvature of the earth and also its absolute dimensions. About the middle of the last century great discussion arose as to whether the spheroidal form of the earth was obate or probate. Measurements in France seemed to show 1t was probate, but that was in opposition to Newton's theory of gravitation-that the cen- trifugal force of the earth. in revolving on It's axis, would naturally produce q spheroid, flattened at the poles-and the two things could not be reconciled. One scientific party followed the French in the beKef that it was prolate and the other Newton, that 1t was obate. Two expeditions were organz- ed and sent forth, one to Peru, on the equator. and the other to Lapland, as near the pole as possible, so as to get the greatest effect. It was seven years before the expeditions got back, and when they compared the measures ob- tained at the equator with those ob- tined at the pole, the question was con- clusively settled that this earth as a spheroid was oblate rather than pro- late, and since that time it has never been doubted. In fact, when these ex- petitions returned they were said to have f1attened not only the earth but Cassini, who had led the probate theory and this verb has a much more forcible meaning in French than in English. Bouguer, one of the scientists who went to Peru on this expedition, made a number of observations on the dens- ity of the earth. He swung a pendu- lum at the top of the Andes and at the bottom, to get the mean density of the earth, as well as the size and shape. This was the first time the resistance of the air was applied to pendulum observation.
 But to estimate the exact size of the earth and the amount of it's curva- ture, great many different arcs have been made through the years, and these were all collected and grouped up to 1S41 by Bessel German. From a discussion of all these measures he determined the figure of the earth, and his conclusions were of course &C., cepted by scientific men in in all their calculations in which these data en- tered. Besseis table were used from 1S41 to 1866. In the meantime every na- tion had been going on with geodetic researches. Col. Clarke of the Royal Engineers of England took all the material that had accumulated up to 1866 and brought out another spheroid. Measures were becoming more and more exact and his figures of the earth is slightly larger and flatter than Bes- sells. The Clarke spheroid, the one now used in the Coast Survey work, was adopted in 1880, and all our tables are made to conform to it. Of course, when we make projections for our larger scale map we make them on the theory that our earth has a cer- tain radius and a certain flattening. All our tables are on that basis. It is from these measures of arcs that the shape of the earth, that is, the fatten- ing, and the size can be learned The tlattening, without reference to it's shape, may also be ascertained by pendulum observations. By swinging