during Absorption of Electrons by Different Metals. 409 



exponential law. At a certain stage there is a sudden 

 increase in the emission. This is followed by a third region 

 in which the current again diminishes with decreasing 

 temperature according to the regular law. 



There are thus two ranges or! temperature in which the 

 thermionic current is stable. These are separated by a region 

 of instability. We shall refer to the two' stable ranges as 

 the low-temperature range and the high-temperaturo range 

 respectively. The heating effect in the case of iron has been 

 examined, both when the osmium was on the low-temperature 

 range and also when it was on the high-temperature range. 

 The numbers are given in the last two rows of the table. 

 The mean of the six values for the low-temperature range is 

 4*88 volts, and of the four values for the high-temperature 

 range 6*72 volts. There is thus a difference of nearly two 

 volts in the effect given by the two ranges. 



We next attempted to make experiments upon the other 

 metals under such conditions that we knew whether the 

 osmium was on the low- or the high-temperature range. At 

 the outset we obtained values for platinum in the neigh- 

 bourhood of 7 volts as against the value 5*5 volts obtained in 

 our previous investigation. We believed at the time that we 

 were working on the high-temperature range ; but that par- 

 ticular filament burnt out, and later on we found it impossible 

 to get a filament which would develop the two ranges. This 

 situation compelled us to desist from the direct line of attack 

 for the moment ; as it is necessary to make a more thorough 

 examination of the thermionic properties of osmium, in order 

 to be able to control the conditions which determine its 

 thermionic emission. We hope to be able to report on this 

 matter at an early date. 



If we return for a moment to the table on page 407 it is a 

 striking fact that four of the mean values, viz. : gold, 7'26, 

 copper 7*1, aluminium 7 '4, and iron (high) 6*72, are equal, 

 within the range of experimental error, to a common mean 

 value 7*11 ; whilst the other five, viz.: nickel 5'3, phosphor 

 bronze 5*8, palladium 5*6, silver 5*15, and iron (low) 4*9, are 

 equal within the same limits to the common mean value 5'oi>. 

 It looks as though the values for gold, copper, and aluminium 

 had all been obtained with the osmium on the high range, 

 and the values for nickel, phosphor bronze, palladium, and 

 silver with the osmium on the low range. It would follow 

 from this that the value of the heating effect is independent 

 of the nature of the metal which receives the electrons, 

 being determined almost entirely by the metal which emits 

 them. 



Phil. Mag, S. 6. Vol. 21. No. 124. April 1911. 2 E 



