Lord Kelvin in 1866 sought to determine the rigidity of the earth from observations of the tides of the cean. His cone Usion was that the earth as a whole is certainly more rigid than glass, but perhaps not quite as, rigid as sttel. The late Dr. Dawson of the Canadian Geological Survey, about 1880, concluded alter care-, fully studying the lornightly tides that the earth was moie rigid than steel. Now Prof. T. J. J. See of the United States navy, by mathematical processes, contends that, accoidmg to Laplace s law. the density at the centor of the earth is equal to that exerted by a Vertical column of quicksilver as long as from St.' Louis to San Francisco.
By considering the pressure throughout the whole earth, Prof. Sue finds that even if fluid the globe would have a rigidity greater than that of. wrong lit it on. He that the average rigidity of the whole mass is. nearly equal to that of nickel steel. lie further contends.- that the rigidity of the earth's crust is about, equal to that of granite, which is one sixth that of steel. and that toward the center the rigidity taj idly increases. At the earth center the impisoned matter is at an enormously high temperature.