abstracts: physics 43 



PHYSICS. — Tables and curves for use in measuring temperatures with 

 thermocouples. Leason H. Adams. Bull. Amer. Inst. Min. Met. 

 Eng. 2111-2124. Sept., 1919. 



Previous publications have called attention to the advantages of 

 standard calibration tables for translating the electromotive force of 

 a thermocouple into temperature, and such standard tables have been 

 given for copper-constantan and for platinum-platinrhodium couples. 

 It has now been found advisable to extend the range of the copper- 

 constantan table so that this couple may be available for measuring 

 temperatures up to 400° and down to — 200° C. A table for chromel- 

 alumel (the Hoskins couple) has also been worked out and the previous 

 platinum-platinrhodium table for temperatures between 0° and 1755° 

 is reprinted without change. The question of fixed- junction correc- 

 tions is discuised and the best methods for making such corrections 

 are described in detail. L. H. A. 



PHYSICS. — Spectral photoelectric sensitivity of silver sulphide and 

 several other substances. W. W. Coblentz and H. Kahler. Bur. 

 Standards Sci. Paper 344. Pp. 18, figs. 17. 1919. 



This paper gives data on the change in the electrical resistance of 

 the sulphides of silver and of bismuth, when exposed to radiations of 

 wave-lengths extending from 0.6 jj. to 3/i. Measurements were made 

 also upon galena, cylindrite, pyrite, and jamesonite, which, however, 

 did not show photoelectrical sensitivity for the highest spectral radia- 

 tion intensities available. 



Both the natural mineral, acanthite, Ag2S, and a laboratory prepara- 

 tion were examined. The latter material, which was hammered into 

 a thin plate, was found insensitive photoelectrically, at room tempera- 

 ture. But at — 157° C. a sharp maximum of photoelectrical sensitivity 

 was observed for radiations of wave-length X = 1.05/x. 



Increasing the intensity of the exciting radiations shifts the maximum 

 of the photoelectrical sensitivity curve toward the long wave-lengths. 



There is no simple law governing the variation in the photoelectric 

 response in silver sulphide with variation in intensity of the radiation 

 stimulus. Mechanical working (hammering into a thin plate) appears 

 to lower the intrinsic photoelectrical sensitivity of acanthite and changes 

 the position of the maximum of spectral sensitivity. A spectral photo- 

 electric sensitivity curve of bismuthinite, Bi2S3, was obtained at — ^166° 

 C. There are maxima of sensitivity at 0.64^1, and i.o8/x, respectively. 



W. W. C. 



