daring the Absorption of Electrons by Platinum. 193 



The corresponding columns give the values o£ the same 

 quantities as in the previous table. The last two experi- 

 ments were made with different intervals of time. In one 

 set the thermionic current was turned on and off every thirty 

 seconds, and in the other set every two minutes. A marked 

 difference between the two values was obtained, but we are 

 inclined to think that a great deal of this arises from some 

 independent cause, as another experiment, made especially to 

 test this point, and which is not recorded in the table, gave 

 a small difference in the opposite direction. It is difficult to 

 get accurate observations with intervals as long as two 

 minutes, and the fact that the value 6*36 for thirty-second 

 intervals is much greater than the number given by the two 

 previous observations tends to shed doubt on this set of 

 experiments. The mean of all the experiments gives 5*81 

 volts for the effect. If the third is rejected on account of its 

 deviation from the mean, and the fourth on account of the 

 time not being the same, the mean of the two is 5*75 volts. 

 This is not very different from the values given by the 

 experiments in oxygen. The fact that it is somewhat higher 

 may perhaps be taken to indicate that there is an apparent 

 increase in the magnitude of the effect when the thickness 

 of the metal used is increased. 



§ 11. Graphical Treatment. 



In order to see at a glance the degree of consistency of 

 the results a graphical method of exhibiting them has also 

 been adopted. Owing to the variation of some of the 

 conditions, such as, for example, the sensitiveness of the 

 galvanometer from one set of experiments to another, change 

 of temperature of the grid, etc., the heating effect for a 

 given number of volts per unit thermionic current as 

 measured in scale readings, does not mean the same thing in 

 the different sets of experiments. It is, therefore, necessary 

 in comparing the different experiments to reduce all the 

 measurements to a uniform scale. This has been done by 

 drawing the best line through each individual series and 

 putting the value of the scale deflexion per unit thermionic 

 current at an arbitrary voltage (as a matter of fact, 12 volts 

 was taken) equal to some arbitrary quantity, say 4. The 

 individual readings for different voltages were then reduced 

 to the scale thus obtained and have all been plotted together in 

 the accompanying diagram (PL III. fig. -4). In this diagram 

 the voltage is represented horizontally and the effect on the 

 standard scale vertically. The -points for the grid saturated 



Phil. Mag. S. 6. Vol. 20. No. 115. July 1910. 



