THE CORE OF THE EARTH

Dominion, Volume 21, Issue 12, 8 October 1927, Page 26

THE CORE OF THE EARTH

From observations it seems that seismic waves start off at a certain speed, but at a depth of sumo 15 kilometres they enter a layer of different material, because at the 'same observing station some waves are found that have travelled directly, while others seem to have traveled taster at a greater depth, writes Harold Jetlu.is, M.A. D.Sc., 1'.1'.5., in an article dealing with’ tlie centre of the earth in the “Daily Chronicle"). At a depth of about 3(1. kilometres they appear to enter another sort of material, because the transmitted waves begin to m*vo at an increased speed again. From hero they proceed without further incident until they get along halfway to the centre, of the earth. Now at tins point a verv remarkable thing happens. lor a third time the compressional waves are split, some of them returning to the surface, tlio others passing on at a reduced speed this time. But while some, of the distort ional waves are reflected back, none of them passes on. Wo know that liquids will transmit the one sort of wave, but not the other. There is only one thing to suppose, therefore—that the earth has a liquid core. . By Considering the earth’s gravitational pull we can calculate its mass. But if we calculate its mass from its measurements and its density near the surface—.allowing for a steady increase of density towards the centre, we find it comes to verv much less. ‘lhe earth, then, must have a very heavy core. Probably it is of liquid'nickel and iron.