V. Bjerknes
Published: 2018-02-05
Total Pages: 434
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Excerpt from Dynamic Meteorology and Hydrography The level surfaces must be carefully distinguished from the surfaces of equal height above or equal depth below sea-level. The intensity of gravity decreases from the pole to the equator. Consequently the unit-mass must be lifted higher at the equator than at the pole, if the same amount of work is to be performed, and thus the same level surface be attained. A surface of equal height above or of equal depth below sea-level must therefore cut through the system of level surfaces. The surface of equal height or depth is a slanting surface, which is not normal to the plumb-line, and on which equilibrium is not possible under the sole action of gravity. If the surfaces were hard and smooth a ball would remain in equilibrium on a level surface. But on a surface of equal height above sea-level it would roll in-the direction from the pole to the equator; and on a surface of equal depth below sea-level it would roll in the direction from the equator to the pole. This property at once shows that the surfaces of equal height or depth are not suitable as coordinate surfaces in problems relating to the statics or the dynamics of the atmosphere or the sea. For this purpose only level surfaces are found suitable. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.