854 Mr. Otto Stuhlmann on Difference in Photoelectric 



The present experiments are an illustration of the fact that 

 by using the emanation of radium, researches on gaseous 

 properties may be carried into new regions ; and work, quite 

 impossible with ordinary gases, becomes practicable and 

 easy by virtue of the very simple and convenient property 

 o£ ionization. 



The writer wishes to express his indebtedness to Professor 

 Rutherford for the very frequent supplies of emanation, and 

 also for his very helpful interest and advice. 



University of Manchester, 

 July 1911. 



LXXXIIL The Difference in the Photoelectric Effect caused 

 by Incident and Emergent Light. Part II. By Otto 

 Stuhlmann, Jr., M.A., Experimental Science Fellow, 

 Princeton University *. 



Introduction. 



IN a previous communication f the writers bowed that when 

 a beam of ultra-violet light, frum an iron arc, impinges 

 on a film of platinum so thin that its absorption can be 

 neglected, the photo-electric effect caused by the emergent 

 beam is greater than the photo-electric effect caused by the 

 incident beam. 



Thus for platinum sputtered from a cathode on quartz 

 plates in vacuo, the ratio of the emergent photo-electric 

 effect to the incident photo-electric effect was as 1*17 to I/O, 

 when the absorption of the millimetre quartz plate on which 

 the platinum film was mounted was allowed for. 



Shortly after a preliminary account of part of the matter 

 described in the above paper had been published J, a notice 

 appeared in 'Nature' by R. D. Kleeman §, who also found 

 that this want of symmetry between the emergent and 

 incident photo-electric effect existed when ultra-violet light 

 fell normally on thin films of platinum sputtered in vacuo. 

 By using a rather thick sputtered film of the metal which 

 allowed only 55 per cent, of the incident light to pass 

 through, he found that the ratio of the emergent to the inci- 

 dent photo-electric effect was as 1/15 is to unity, without 



* Communicated by Prof. O. W. Richardson. 

 t O. Stuhlmann, Jr., Phil. Mag. xx. p. 331, Ausr. 1910. 

 X Nature, May 12, 1910. 



§ Nature, May 19, 1910, Also later Proc. Roy. Soc. A., vol. lxxxiv. 

 (1910). 



