356 Mr. F. C. Brown on the Kinetic Energy of 



V is the potential at time t, n is the number of ions emitted 

 by the lower plate per second, and w , r , and ic are the velocity 

 components at the time of emission. 



In the particular case where the distribution of velocity 

 among the ions follows Maxwell's laws, this equation re- 

 duces to 



log-j— £V, . ..... (2) 



where i is the current against a potential V, to is the current 

 at zero potential, ve is the quantity of electricity required to 

 liberate half a cubic centimetre of hydrogen in a water 

 voltameter at zero degrees centigrade and 760 millimetres 

 pressure, 6 is the absolute temperature, and R is the constant 

 in the equation pv — ^6 taken for unit volume of gas under 

 standard conditions. 



We shall now describe the results of experiments which 

 show that this relation is fulfilled within the limits of 

 experimental error. 



Experimental Res ults. 

 As the determination of the kinetic energy was based upon 

 the rate of charging up of an insulated plate by the positive 

 ions, it was quite necessary that there should be no negative 

 ions emitted to the upper plate. The positive ionization 

 appears greatest in platinum when it is first heated. After 

 a few hours'* heating in a high vacuum it disappears almost 

 completely. For one platinum strip the magnitude of the 

 positive ionization decayed with the time of heating about 

 as shown in the accompanying table. 



Table I. 



Date. 



Hours 

 heated. 



Dec. 2 







Dec. 14 



H 



5> 



U 



Dec. 18 



9 



Dec. 26 



13 



Dec. 28 



18 



Dec. 29 



oi 



Positive 

 current, 

 amperes. 



Temperature- Pre 

 resistance, i jjj. 



scale. 



5xl0- 9 



13xl0~ 9 

 6X10" 10 

 SxlO" 11 



3x10" 

 10 



-12 



1X10 



7800 

 7800 

 7800 

 7800 

 7500 

 7400 

 7500 



•01 

 •006 

 •006 

 •030 

 •009 

 '60-000 

 '60000 



Negative 

 potential on j 

 Upper plate 



40 



400 







i w.3 



; ^2 



