GEOPHYSICAL LABORATORY.* 



Arthur L. Day, Director. 



The activities of the Geophysical Laboratory for the past year 

 have been confined to the development of war problems in direct 

 association with the War Industries Board, the Bureau of Mines, 

 and the Nitrate Division of the Bureau of Ordnance of the War De- 

 partment. All other research work has been laid aside. 



Some account of our work on optical glass was given in the annual 

 report of this department for the year 1917, but for reasons of expedi- 

 ency its further details must await a more opportune time of publica- 

 tion. It has also been deemed unwise, for military reasons, even to 

 indicate at this time the other problems upon which the laboratory 

 is now engaged. 



PUBLICATIONS. 



A number of publications are re\dewed in the paragraphs which 

 follow, being for the most part the records of researches in progress 

 at the time of the entry of the United States into the war. A portion 

 of this work has been brought to a tentative or final conclusion as 

 opportunity offered and has been published during the current year. 



(1) Heat convection in air, and Newton's law of cooling. Walter P. White. Phys. 



Rev., 10, 743-755 (1917). 



In very narrow layers of air between vertical surfaces at different tempera- 

 tures the convection currents, in the main, flow up one side and down the 

 other, with eddyless (stream-line) motion. It follows that these currents 

 transport heat to or from the surfaces only when they turn and flow horizon- 

 tally, from which fact it follows, in turn, that the convective heat transfer is 

 independent of the height of the surface. It is, according to the laws of eddy- 

 less flow, proportional to the square of the temperature difference and to the 

 cube of the distance between the surfaces. As the flow becomes more rapid 

 (e.g., for a 20° difference and a distance of 1.2 cm.), turbulence enters, and 

 the above relations begin to change. The change is apparently gradual, and 

 the present results, as well as some obtained by other experimenters, are 

 rather negative as to the possibiHty of expressing the flow simply for the 

 corresponding range of conditions, which covers those most usual in calori- 

 metry. The results, however, are sufficient to serve as a practical guide in 

 calorimeter designing. For the dimensions tested, the transmission of heat 

 by convection in horizontal layers was a Httle over twice that in vertical. 



(2) A silica-glass mercm-y still. J. C. Hostetter and R. B. Sosman. J. Wash. Acad. Sci., 



8, 11-15 (1918). 



A description, with specifications and dimensional drawing, of a vacuum 

 mercury-still made of fused silica ("quartz glass") and heated electrically. 

 It has the advantage over ordinary glass stUls of avoiding the danger of col- 

 lapse due to overheating. 



♦Situated in Washington, D. C. 



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