Temperature upon Photo-electric Effects in High Vacuum. 197 



very rapid in this case at 180° C, while in the case of the 

 tube used before it did not appear until the temperature had 

 been raised to 360° 0. or 370° 0., may possibly be due to the 

 fact that the electrode in that case was composed only of 

 aluminium, while in this case it was composed of a large 

 number of different metals, each of which may have a charac- 

 teristic temperature at which this effect appears. On the 

 other hand, it may be due to the fact that occluded gases 

 were very thoroughly removed from the aluminium electrode 

 of fig. 1 by using it for several hours as the cathode of an 

 induction-coil discharge, and also by continuous heating ; 

 while, with the bulb here used, although the temperature was 

 kept at 400° C. during exhaustion, no attempt was made to 

 use an induction-coil upon it for fear of producing thereby 

 differences in the surfaces of the electrodes (cf. § 7). The 

 subject is one which is being given further study. It has no 

 immediate bearing upon the main purpose of this investi- 

 gation. 



Table II. 



Eate of Discharge in Scale Divisions. 



Metal. 



= ! T= 

 C. ! 35° C. 



Copper 25-10 



Gold 24-70 



Nickel 2400 



Brass 23*80 



Silver 17'16 



Iron 16-40 



Aluminium... 1490 

 Magnesium... 1100 

 Antimony ... 4*00 



Zinc 1-20 



Lead j 0*90 



25-15 



24-60 



23-96 



23-85 



17-20 



16*25 



15-00 



11-12 



4-00 



1-30 



0-90 



T= 



T = 



40° C. 



50° C. 



25-20 



25-25 



24-55 



24-70 



23'98 



23-90 



23-95 



24-UO 



1715 



1720 



1630 



16-20 



14-85 



14-86 



11-10 



11-05 



4-10 



4-00 



1-31 



1-35 



0-90 



0-88 



T= 

 65° C. 



25 00 



24-80 



24-05 



23-85 



17-10 



16-36 



15-06 



11-00 



4-00 



1-20 



0-90 



T= 



T= ! 



80° O. 



100° C. | 



25-05 



24-80 



24-75 



24-40 | 



23-90 



23-55 ! 



23-90 



23-40 



17-00 



16-90 



16-55 



1615 ! 



1490 



14-50 



10-97 



10-90 | 



4-00 



3-90 



1-20 



1-24 



0-90 



0-91) 



T= 



125° C. 



24-75 



2400 



23-40 



23-40 



16-77 



1600 



14-55 



10-90 



3-95 



M0 



090 



Confining attention for the present to the horizontal rows 

 in Table II., it will be seen that the observations (which 

 extend over a period of several weeks) are on the whole 

 remarkably consistent, the observational error, save for the 

 very small deflexions^being seldom more than two per cent. 

 Within the limits of this error the table shows that a rise in 

 temperature from 25° C. to 125° C. has no effect whatever 

 upon the rate of discharge of negative electricity from any 

 of the metals experimented upon. The uniformity in the 

 minute decrease in the values under 125° C. is undoubtedly 



