Physics of the Earth

Abstract

THE nature of the earth's interior has been a subject of speculation for thousands of years. Ancient philosophers, from the Babylonians onwards, firmly held the belief that the depths were largely occupied by water. Even in the volcanic regions of the Mediterranean, where the subterranean world was naturally associated with ideas of internal fire, this belief was not excluded. Moreover, the winds of the Aeolian Isles were regarded as draughts generated from immense air-filled cavities by the action of the volcanic hearths. These traditional views persisted unchallenged until well into the seventeenth century. In 1695, for example, we find them repeated with characteristic exuberance by John Woodward. But already less fanciful notions were beginning to be formulated. Leibniz in 1680 had clearly expressed the idea of a crystalline crust resting on a molten interior; and a century later (1788) Benjamin Franklin asks: “Can we easily conceive how the strata of the earth could have been so deranged if it had not been a mere shell supported by a heavier fluid?” However, before another century had elapsed, Hopkins and Kelvin had shown that a fluid interior was inconsistent with the phenomena of precession and the tides, and geologists were left to puzzle over Franklin's problem as best they could. With the present century has come the realization that ‘non-fluidRsquo; or ‘solid’ does not necessarily imply the crystalline state; vitreous material would fulfil still better the conditions imposed on speculation by the earth's behaviour.

Physics of the Earth

7: Internal Constitution of the Earth. Edited by Prof. Beno Gutenberg. Contributors: L. H. Adams, Reginald A. Daly B. Gutenberg, Harold Jeffreys, Walter D. Lambert, James B. Macel-Wane, S. J., C. F. Richter, C. E. van Orstrand, H. S. Washington. Pp. x + 413. (New York and London: McGraw-Hill Book Co., Inc., 1939.) 30s.