626 Profs. Cooke and Richardson on Absorption of 



The method will be clearer after reference to fig. 1. This 

 shows one of the two arrangements used which, for reasons 

 which will be clear later, may be referred to as the " standard 

 shunted ? ' arrangement. The osmium filament L is placed 



in the arm EF of the bridge. The adjacent arm CE carries 

 a standard resistance of 10 ohms capable of taking a large 

 current without heating. The resistance of the filament L 

 was comparable with 4 ohms at the temperature of the ex- 

 periments. The resistances CD and DF were 100 times CE 

 and EF respectively, so that only one per cent, of the bridge 

 current flowed along CDF. With this arrangement of re- 

 sistances the same current maybe used to actuate the brido-e 

 and to heat the filament, and on account of the large current 

 flowing down the arms CEF very small changes of resistance 

 may be detected. The main current was supplied by the battery 

 B : of 12 or 24 volts, regulated by the rheostat Rh 1? measured 

 by the ammeter A and reversed b}^ the reversing switch K^ 

 It also passed through a standard 1 ohm resistance at NM. 

 By means of the key K 3 this could be shunted by a standard 

 100 ohm resistance, thus producing a small known change 

 in the heating current through L. The emitted electrons 

 flowed from L to the surrounding cylinder H. They were 

 driven by the high potential battery B 2 . This was placed 



