GEOPHYSICAL LABORATORY* 



Arthur L. Day, Director. 



After a scientific undertaking is organized, properly equipped, and fairly 

 started upon its way, its best report of progress is its published work. The 

 Geophysical Laboratory has entered upon a systematic study of rock formation. 

 This means the study of the relation of the component minerals which go to 

 make up the typical rocks. It may be directed toward the great igneous rock- 

 masses which are first in structural importance, toward the metamorphic rocks 

 in which much earth history is recorded, or toward the ore deposits which are 

 first in economic interest. The choice at the beginning has no especial signifi- 

 cance. Researches must eventually be undertaken in all these directions. The 

 most important questions at the beginning are: (i) practicability, to start 

 with simple and accessible relations — the behavior of a single mineral or sim- 

 ple mixture of two — and to proceed from these to more complicated cases with 

 the advantage of more competent experience; (2) quantitative methods, to 

 use pure minerals which are not rendered abnormal through by-mixtures of 

 unknown behavior, and to measure the forces (pressure, temperature) to 

 which they are subjected. 



It must be an organized efifort, for chemistry must guarantee the initial 

 purity of the component minerals, and physics must provide and measure the 

 temperatures and pressures, physical chemistry must correlate the reactions, 

 and petrology must fit the product into its proper niche in the earth's rock- 

 system. This, in a word, is the Geophysical Laboratory organization. A sub- 

 stantial building has been provided for it, which was described in the Di- 

 rector's report of a year ago, and the work of this year has served to bring 

 the plant up to its full efficiency. 



Two branches of the work are not represented in the published papers of 

 this year and may receive brief mention here : 



Lime- Alumina-Silica Mixtures.] — All of the mixtures between pure silica 

 and pure alumina have been fused and examined microscopically. The appli- 

 cation of our usual methods discovers only one compound between these two 

 oxides — ALSiOg, or sillimanite. The pure mineral prepared in the laboratory 

 presents several interesting details of structure and has an index of refrac- 

 tion slightly lower than the natural mineral. Its melting-point falls a little 

 higher than that of platinum. Some work published by the Konigliche Por- 



* Address : Upton_ Street, Washington, D. C. Grant No. 476. $40,000 for geophysical 

 research. (For previous reports on geophysical work see Year Books Nos. 3. 4, 5, and 6.) 

 t E. S. Shepherd and G. A. Rankin. 



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