Temperature upon Photo-electric Effects in High Vacuum. 209 



with the glass. At any rate the following observations upon 

 silver and aluminium exhibit no fatigue effects which persist 

 longer than three minutes. Aluminium and silver were 

 chosen for these experiments because, according to Laden- 

 burg, the former shows no fatigue at all, while the latter 

 shows the largest fatigue effects of any of the metals. 



The electrometer and wheel were charged to a potential of 

 about 15 volts, which under the conditions of this experiment 

 corresponded to a deflexion of about 500 scale -divisions. 

 The battery connexion was broken, the light turned on, and 

 the discharge during a period of 30 seconds observed. The 

 experiment was then repeated at the end of a few minutes to 

 make sure that consistent results were being obtained ; then 

 the light was left on continuously for a period of several 

 minutes, the potential being maintained at 15 volts, and two 

 or three minutes after turning off the light the discharge 

 during a 30-second exposure was observed again. 



Table IV. 



Aluminium. 



Silver. 



Discharge 



Time. in 30 sec. 



1.26 p.m 45'1 mm. 



Time. 



10.10 A.M 



10.18 A.M 



Continuous exposure 

 from 10.27 to 10.33 a.m. 

 10.36 a.m 



Discharge 

 in 30 sec. 

 49-3 mm. 

 49-4 „ 



49-2 „ 



1.33 p.m 45-0 „ 



Continuous exposure 

 from 1.39 to 1.55 p.m. 

 1.57 p.m 44/5 „ 



1 



These observations show no evidence of any fatigue effects 

 in the case of either aluminium or silver. It is scarcely to be 

 doubted that if our silver surface had had a high polish to 

 begin with, it would have shown the same permanent fatigue 

 effect observed by Ladenburg. Our result differs from his 

 only in that we succeeded in obtaining surfaces which show 

 constant rates of discharge, while with the treatment to which 

 he subjected his surfaces no such constancy seemed to be 

 obtainable. 



It may be observed that the entire lack of fatigue effects 

 in a vacuum, even in the case of a single metal like aluminium, 

 in regard to which Ladenburg's results and our own are in 

 agreement, precludes the possibility of such an explanation 

 of fatigue phenomena as that offered by Ramsay and Spencer, 

 namely, that the surface is first denuded of its metallic elec- 

 trons, and later of electrons which must be thrown off from 

 the body of the atom. 



Phil. Mag. S. 6. Vol. 14. No. 79. July 1907. P 



