444 Alleged Scattering of Positive Electricity by Light. 



expected that any discharge possibly produced by light at 

 the anode would also be in some way dependent upon the 

 direction of the light- vibrations toward the surface of the 

 anode. The experiments made in this direction gave, how- 

 ever, a negative result : if we allowed a ray of light to 

 fall through a Nicofs prism upon the fluid surface of the 

 sodium-potassium alloy which formed the anode, and altered 

 the position of the plane of polarization by turning the Nicol, 

 we found the photoelectric dispersion to be independent of 

 the azimuth of the light. 



It must be remarked that in the " reversed " arrangement 

 of the cell here employed the current strength, even in strong 

 light, is far too small to give a measurable deflexion, even on 

 the very sensitive galvanometer which we employed to measure 

 the photoelectric currents. We therefore employed the same 

 method which we had used in the experiments upon ultra- 

 violet light, i.e. we connected the alkali-metal surface with 

 the positive pole of the above-described battery, and the 

 opposed platinum electrode with the quadrant electrometer. 

 The passage of electricity through the cell betrayed itself 

 then by the constant increase in the deflexion of the electro- 

 meter-needle. A constant condition of the instrument may 

 be attained by making an earth connexion through a very 

 large resistance (a pencil mark on an insulating surface) to 

 the wire leading to the electrometer. 



Not only does the fact that the transference of electricity 

 is not affected by change in the direction of the light- vibrations 

 with respect to the plane of the anode prove that the seat 

 of photoelectric action is not at the anode, but we have the 

 further evidence that this action is perceptibly increased if 

 the platinum wire which serves as kathode is exposed to the 

 direct action of the light. It even continues of the same 

 intensity when by inclining the bulb the alkali-metal is made to 

 flow over into the side bulb and is thus removed from the cell*. 



Since a clean platinum-wire in a vacuum shows no photo- 

 electric action in ordinary light, its sensitiveness can only 

 have been communicated to it by contact with the alkali- 

 metal or its vapour. As we see, the result of this experiment 

 also leads us to the conclusion that the light has acted not on 

 the anode of alkali-metal but on the platinum kathode made 

 sensitive by its superficial coating, and we might expect that 

 the " reversed " cell would lose its sensitiveness upon ignition 

 of the platinum wire. But, as we have said, this expectation 

 was, curiously enough, not verified by experiment. There 



* The form of the cell is shown in fig., Wied, Ann, xlii. p. 564 (1891) j 

 see also Phil. Mag. 1896, xli. p. 220. 



