. Carnegie Institution of Washington publication. GRAVITY AND GRAVITY POTENTIAL. II approximate hydrostatic equilibrium of the masses in the earth's crust is verified. More recently this verification has also been extended to the open sea by the measurements of the Nansen Expedition in the Polar Sea and those of Hecker on the Atlantic* These results are very important for dynamic meteorology and hydrography, as they show that the gravitational field of force in atmosphere and sea is much more regular than originally supposed. The continental masses present above sea-level do not cause perturba


. Carnegie Institution of Washington publication. GRAVITY AND GRAVITY POTENTIAL. II approximate hydrostatic equilibrium of the masses in the earth's crust is verified. More recently this verification has also been extended to the open sea by the measurements of the Nansen Expedition in the Polar Sea and those of Hecker on the Atlantic* These results are very important for dynamic meteorology and hydrography, as they show that the gravitational field of force in atmosphere and sea is much more regular than originally supposed. The continental masses present above sea-level do not cause perturbations of the field. On the contrary, they make it more regular, because they compensate for subterranean mass defects. Neither does the sea, with its smaller density, complicate the field, because there are compensating excesses of mass below the sea-bottom. The only perturbations of the field are due to irregularities of local topography or of local mass distribution sufficiently small to be balanced by the elastic stresses which they produce in the earth's crust. We shall make no corrections for these local irregularities. The reduction to sea-level of the numerical value g\ of the acceleration of gravity found by pendulum experiments at the earth's surface at the height z above sea-level will be given by the formula (a) £*o =£"i + * the correction term being the same as that of formula section 7 (a), or of table 1 m of Meteorological Tables, but with the sign reversed. We shall use this reduction consistently in cases where we start with really measured values of the accelera- tion of gravity at the earth's surface. It will be convenient, as all heights are measured from sea-level, and the reduction will bring in no errors in the values of gravity calculated for the free air, as errors possibly introduced by the use of for- mula (a) for reductions downward will drop out again by the reduction upward, according to formula section 7 (a). If no measurements of


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