672 



Prof. J. Patterson on the Electrical 



positive to the cathode. In platinum, however, the results varied 

 considerably. The cathode, after being used for some time, 

 was tested against a freshly deposited film and gave a difference 

 of 0*047 volt, the film being positive to the cathode. After 

 carefully polishing the cathode and depositing some more 

 films from it, these were tested agaiust the cathode, and a 

 difference of 0*15 volt was obtained, but this time the cathode 

 was positive to the film. The cathode and film were next 

 put in a weak solution of platinic chloride, and they then 

 gave a difference of 0*09 volt, the cathode being positive to 

 the film. The film, which was at first positive to the cathode, 

 was again tested about a month afterwards with the freshly 

 polished cathode, and this time it was negative to the cathode 

 and gave a difference of 0'015 volt. 



Photo-Electric Effect and Radiation from Hot Films. 



Experiments w T ere made to see whether there was any 

 difference between the rate at which the cathode and the film 

 deposited from it discharged electricity under the influence 

 of ultra-violet light, but no difference was detected. 



Experiments were also made to see whether it was possible 

 to get negative radiation from hot platinum films in vacuo. 

 The films were deposited on mica and electrodes clamped on 

 the ends. The film was heated by a steady current from a 

 number of accumulators which were insulated. The film 

 was charged to a known potential. The leak was observed 

 between the film and an insulated electrode which was placed 

 above it. The electrode was connected to one pair of 

 quadrants of a quadrant-electrometer, the other pair being- 

 earthed. It was not possible to heat the film hot enough to 

 get the negative radiation, but the positive radiation was 

 obtained. The positive leak increased very rapidly with the 

 increase of current through the film, but did not reach a 

 maximum when the film broke down. Table XI. shows the 



Table XI. — Radiation from Hot Pt. Film. 



Current in amperes 



Potential on film 



Time of 200 div. on 



through film. 



in Tolts. 



electrometer scale. 



Oo 



+40 



no leak. 



0-6 





., 



0-72 





530 sec. 



081 





80 „ 



093 





„ 



1-0 





s^ , 



11 





lf„ 



