C. A. Butman — Effect of Phosphorescent Material. 133 



Art. XIII. — The Photoelectric Effect of Phosphorescent 

 Material • by Chester A. Butman.* 



The first work done on the photoelectric effect of phos- 

 phorescent materials was that of Elster and Geitel.f Other 

 workers are G. C. Schmidt,} P. Lenard and Sem Saeland,§ 

 and Maryan Grotowski.f The following facts asserted by 

 Lenard and Saeland were confii-med by me, for CaBiNa, the 

 most strongly photoelectric substance nsed by them. 



(A) The photoelectric effect stops the moment the light is 

 shut off. 



(B) Light which does not produce phosphorescence does not 

 produce the photoelectric effect. 



(C) If red is added to a color causing phosphorescence, it 

 has no influence on the magnitude of the photoelectric effect. 



In addition to the foregoing, the velocities of the electrons, 

 ejected when the material is exposed to light which has passed 

 through glass, have been carefully determined. In order to 

 gain more knowledge about the velocities, it was found neces- 

 sary to make a study of the photoelectric fatigue of this 

 material. This fatigue in this case is different from the photo- 

 electric fatigue of metals, in that it takes place in a high 

 vacuum and recovers after a lapse of time when not exposed 

 to the light. 



The source of light adopted was the carbon arc which was 

 run at 10 amperes and 65 or 70 volts. This provided a light 

 of constant intensity as was shown by being able to repeat 

 readings exactly. The light which fell on the material passed 

 through a glass condensing lens. 



The electrometer was of the Dolezalek type, used with a 

 quartz fiber suspension. The needle was charged with 80 volts 

 every day. The sensitiveness was about 1,500 millimeters per 

 volt with the scale about 70 cm distant. The deflections were of 

 the same magnitude along all parts of the scale. 



The highest vacuum used was -00001 mm of Hg as recorded 

 by the McLeod gauge ; the lowest, -03 mm . The vacuum was 

 maintained constant by running a Gaede pump to take up any 

 small leak. Tests were made of the photoelectric effect at dif- 



* See also abstract of article read before tbe American Physical Society, 

 Dec. 30, 1911, Physical Review, p. 158, 1912. 



t J. Elster and H. Geitel, Ann. Phys., xxxviii, 508, 1889; xliv, 722-736, 

 1891. 



X G. C. Schmidt, Ann. Phys., lxiv, 708-724, 1898. 



§ P. Lenard and Sem Saeland, Ann. Phys., xxviii, 476-502, 1909. 



|| Maryan Grotowski, These l'Universite de Fribourg, Librairie de Juleu 

 Eousset, Paris, 1910. 



Am. Jour. Sci.— Fourth Series, Vol. XXXIV, No. 200.— August, 1912. 

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