Recent Additions to Ideas Regarding the Internal Structure of the Earth ¹

Abstract

BEYOND the superficial observations made by geologists, not extending more than about one two-hundredth of the radius below the surface, even by indirect means, we are, dependent on mathematicians for our ideas regarding the physical state of the earth's interior; these ideas are based on extrapolation from physical constants obtained in the laboratory, and their variety extends to the number of possible permutations and combinations of the three physical states of matter—solid, liquid, and gaseous. Halley's conception of a core and shell rotating at different speeds has been revived by Sir F. J. Evans (1878) and by the distinguished founder of this series of lectures to explain the secular variations of magnetism. The Laplacian hypothesis, based on Clairault's theorem, is now being superseded in many, minds by Chamberlin's planetesimal theory, after having inspired pfitrologists with a vain hope of finding traces of the primeval slaggy crust among the Archaean gneisses. Astronomers prefer a solid globe, but on grounds different from those assumed by Hopkins and at first accepted by Lord. Kelvin. Arrhenius concludes in favour of a gaseous core, like that postulated by Ritter, but of larger dimensions than the gaseous core suggested by Dr. Wilde.