Vw,. X, No. 3
GLASS, ITS COMI'OSITION AND PIIOI'ERTIES TABLE VI Thermal Conductivity
Literature Cited (I) (2)
NBUMANN. Z. a w g e ~ C . l ~ m . 38, , X l i (1925); 40, 9153 (1W.i); 42, 836 (1929). MOREYand BOWEN.I . P h y s Clrem, 28, l l l i i (1924); KRACRK. ihid.,34, 1583
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( 3 ) MOREYand BOWEN.I. SOC.G l i m T K ~. .9... 22G f1!32$): . . . MORE\,.I.A m . Cpmnr. SOL,13, 683 (1930). OTTO."Verh. des Yereins dcs Gcwerhfleiss," 1887.. D. ( 4 ) SCHOTT, . 799. (6) Most of the data of Table 11, as well as of the succeeding tables, are taken from "Properties of Glass." GEORGEW. "International Critical Tables." vol. 2, p. %i, MOREY. (fi) For the details of the K10-CaO-Si02 system, see MOREY,BOWEN.and KRACEK, I.Soc. Glass Tech.. 14, 149 (1930). Ind. Eng. Chem., 21, 174 (1929). ( i ) LAUBENGAYBR, ONNESand BRAAK. Vwdog. A k d . Wettenschappen Amsterdam. 16, (,8) KAMMERLINCH xno (1908).
Earth's Core Composed of Metallic Iran and Nickel. Though it sounds like an unsolvable riddle, perfection of modern scientific methods and instruments have wrested from the world that its core is formed of metallic iron with a little nickel. This conclusion, generally accepted among scientist?, dashes speculation which has persisted to recent years that the earth, because it is heaviest a t the center, has a heart of gold. While not troubling t o contradict this Jules Verne conception of fabulous wealth unattainahly hidden in the middle of the globe, Dr. L. H. Adams of the Geophysical Laboratory of the Carnegie Institution of Washington tacitly refutes any golden dreams of the earth's interior in a recent report to the Engineering Foundation. This earth is made up almost entirely of four elements, iron, magnesium, silicon, and oxygen, Dr. Adams says. And the remaining 88 elements (including gold, silver, and platinum) are confined to the thin film called the crust. Directly beneath the relatively thin layer of sedimentary rocks a t the surface, there is a first layer of granite ten miles thick; below that a twenty-mile layer of basaltic rock. Two thousand miles of peridotite rock (consisting of iron magnesium silicate) come next, while the central core of 4000 miles diameter is formed of metallic iron with a little nickcl. Earthquake waves yielded the important key to the secret of the earth's composition. Earthquakes of any considerable magnitude produce elastic waves, some of which travel along the surface of the earth and others pass through it. By measuring the acceleration and retardation of these waves on passing through the earth a t various depths, the experts are able t o judge what sort of rocks and minerals intervene. According to its elasticity, each different kind of rock has a different effect on the speed of the waves passing through it and so it is possible to judge the kinds of strata traversed.-Science Service
