Temperature upon Photo-electric Effects in High Vacuum. 201 

 Table III. 



Metal. 





26° C. 



Silver 



1-340 



Iron 



1-225 



Gold 



1-215 



Brass.. 



Copper 



1-174 

 1-135 



Nickel 



1-126 



Magnesium ... 

 Aluminium ... 



Antimony 



Zinc 



•839 

 •738 

 •394 

 •197 



Lead 



•0 







Potentials in Volts. 



T = 



40° 0, 



55° C. 



T = 



60 c C. 



1-340 



1-342 



1-224 



1-224 



1-217 



1-215 



1-170 



1-180 



1-132 



1-130 



1-126 



1-130 



•840 



•840 



•738 



•738 



•395 



•390 



•197 



•199 



•0 



•0 



1-339 



1-230 



1-214 



1-176 



1-128 



1-130 



•842 



•735 



•395 



•192 



■0 



T= T = 



80° C. I 95° C. 



338 

 220 

 215 

 181 

 126 

 122 

 835 

 740 

 396 

 190 

 



1-336 



1-219 



1-213 



1-182 



1-125 



1130 



•840 



•738 



•390 



•188 



•0 



because it confirms, in a wholly new way, the conclusion 

 which it has been heretofore necessary to draw from the fact 

 that the ratio of the specific heats of monatomic gases reaches 

 the theoretical limit, 1'67 ; a value which, according to the 

 kinetic theory, it could reach only if no part of the energy 

 which goes into such a gas when the temperature is raised 

 is expended in producing sub-atomic changes of any sort. 



The results in this table also lead from a new point of view 

 to Lenard's conclusion, that the only appreciable forces which 

 hinder the escape of the electron from the metal are electrical 

 in nature ; for it will be observed that the potentials at 

 different temperatures agree in most cases to within two or 

 three parts in a thousand ; but if the specific attraction of 

 matter for electricity were an appreciable part of the forces 

 which cause the electron to return to the metal, then we 

 should expect the variations of this type of force with 

 temperature as shown by thermo-electric phenomena to cause 

 a variation in the potential assumed. No trace of such an 

 effect is observable. 



7. Independence of the Positive Potential assumed upon 

 the Intensity of the Source. — It seemed worth while, at least, 

 to test with all of the eleven metals here used, Lenard's con- 

 clusion as to the independence of the positive potential upon 

 the intensity of the source*. Hence the intensity was varied 

 both by changing the distance of the source from the wheel 

 and by altering the capacity in parallel with the spark so as 

 to make a spark of greater or less brilliancy. In every case 

 the final position of the needle was precisely the same, 



Lenard, Ann. d. Pltys. ii. p. 355 (1900). 



