574 abstracts: spectroscopy 



PHYSICS. — Spectro-radiometric investigation of the transmission of 



various substances. W. W. Coblentz, W. B. Emerson, and M. 



B. Long. Bur. Stands. Sci. Paper No. 325. Pp. 24. 1918. 



This paper gives the spectral transmission of various substances, 



especially colored fluorite and colored glasses. Some of the substances 



described in this paper provide a simple means of obtaining narrow 



spectral bands of energy of high intensity and large area without 



employing a spectroscope. By properly combining these substances 



one can obtain a screen having a narrow band of high transmission 



at 0.38/x, O.S/i, O.SSm, 0.7m, O.Sai, In, and 2.2^. The data on glasses 



are also useful in connection with the question of protecting the eyes 



from injurious radiations. W. W. C. 



PHYSICS. — The photoelectric sensitivity of bismuthinite and various 

 other substances. W. W. Coblentz. Bur. Stands. Sci. Paper No. 

 322. Pp. 14. 191H 

 This paper summarizes the results of an investigation of various 

 substances (1) for an increase in electrical conductivity caused by the 

 action of light upon them, and (2) for photoelectric activity when they 

 were charged to a negative potential, in an evacuated chamber, and 

 exposed to light. Pure gallium and silver sulphide were found to have 

 but small photoelectric activity when charged to a negative potential 

 and exposed to light. No change was observed in the electrical con- 

 ductivity of tellurium, boleite, pyrite, silicon, and mixtures of the 

 sulphides of lead and antimony, when e^cposed to light. An increase in 

 conductivity was observed in crystals of bismuthinite, cylindrite, mo- 

 lybdenite, selenium, stibnite, boulangerite, jamesonite, and silver 

 sulphide when exposed to light. 



Experiments are described in which some of these substances were 

 joined through a battery to the grid circuit of an audion amplifier and a 

 telephone. The light stimulus was interrupted by means of a rotating 

 sectored disk, as used in Bell's selenium photophone. When using a 

 cell or crystal of selenium the fluctuations in light intensity produced 

 a sufficient change on conductivity to cause a musical note in the 

 telephone. Similarly, in some samples of bismuthinite and of molyb- 

 denite, a change in conductivity was produced, whiclr»caused an audible 

 sound in the telephone receiver. Further experiments are in progress 

 to determine to what extent and for what wave-lengths this is a true 

 photoelectric change (increase) in conductivity, and to what extent 

 it is caused by fluctuations in temperature with a resultant change in 

 resistance within the crystal. W. W. C. 



