during the Absorption of Electrons by Platinum, 185 



property of relatively large negative thermionic emission, 

 and corresponds to a diminution in the value of w. It 

 therefore seemed desirable to examine whether this difference 

 in the power of thermionic emission produced by saturating 

 the metal with oxygen and hydrogen respectively had its 

 counterpart in the heating effect under investigation. 



Furthermore, in order to examine whether the effect 

 measured depended very much on the geometrical configura- 

 tion of the platinum forming the grid, experiments were 

 also made with a grid consisting of platinum wire of 

 circular section -0012 cm. in diameter. The length of the 

 wire in this grid was approximately 36 cm. In this case 

 the filament was not subjected to the electrolytic treatment 

 described above, the effect being measured only for the 

 natural state of the metal. 



§ 6. Typical Experiment, 



The method of observing can best be made clear by 

 describing a typical set of observations. In every case the 

 current-E.M.F. curve w T as first determined, and this was 

 usually repeated at the end of the set. Generally speaking 

 the thermionic current rose gradually during the course of 

 the series of observations, so that at the end the saturation 

 current would often be twice as great as at the beginning. 

 It was also, as a rule, somewhat more difficult to saturate, as 

 saturation is reached with a lower voltage the smaller the 

 current. In this experiment the values of the saturation 

 currents are given in the following table. The first horizontal 

 row gives the values of the negative voltage applied to the 

 negative end of the filament. The second row gives the 

 corresponding values of the currents at the beginning, and 

 the third row those at the end. In the second row the unit 

 of current is 5'66xl0~ 6 ampere, while in the third row it 

 is 10*4 x 10~ 6 ampere. The current-E.M.F. curves always 

 possess the same characteristics. 



Current, and Electromotive Force. 

 ..0123 4 5 6 7 8 9 



.. -2 -9 3-0 7-2 12-9 19'2 25-1 30-7 33-5 34-9 

 .. -4-1-0 2-3 5-4 9-6 147 199 246 287 31-0 



For very low voltages the current increases very slowly 

 with the applied E.M.F. This is followed by a short range 

 of voltage along which the current increases very rapidly 

 and is very nearly a linear function of the voltage. This 



11 



15 



24-2 



36-2 



38-2 



37-7 



32-5 



34-9 





