226 MM. Elster and Greitel on the Electro-optical 



This independence is a consequence of the fact that with 

 increasing angle of incidence the surface illuminated increases 

 in the same ratio as the illumination of the unit-surface de- 

 creases. 



In proof of what has been said, we give the two following 

 series of observations : — 



Natural Light. 

 18 Nov. 1894. 



Angle of Incidence 0° 



25 



» i» 45 



60 







I. Liquid Metal. 

 (KNa-alloy.) 

 10-2 

 155 

 44-2 

 567 

 8-4 



H. Solid Metal. 

 (Surface rough, but as 

 smooth as possible.) 

 34-0 

 33-5 

 330 

 30-5 

 33-1 



Since, then, it is possible without the aid of polarization, 

 simply by changing the angle of incidence, to show the in- 

 crease in the photo-electric action of a ray of light which takes 

 place when the vibrations of light have a component at right 

 angles to the kathode, it was easy to make the like experi- 

 ment with ultra-violet light ; which, as we remarked at the 

 outset, it is difficult, — possibly impossible with the usual means 

 — to obtain in the condition of linear polarization. We have 

 then the advantage that the kathode may be made of any 

 metallic substance we like, and may be used in the open air. 



Fig. 2. 



The arrangement of the experiment was as follows (fig. 2) : — 

 A condenser C was connected with a large inductorium J, 

 the brilliant discharge of which took place between two zinc 

 points S and S' in the focus of a lens Q of quartz. The rays 

 thus made parallel fell upon a plate P of amalgamated zinc 

 placed upright, which was capable of rotation over a gra- 

 duated arc K about an nxis at right angles to the direction of 

 the rays of light. A wire frame n, nf connected to earth, and 



