[scott] 



ELECTRICAL RESISTANCE THERMOMETERS 



155 



ance. When balance is obtained, the resistance of the thermometer 

 coil and its segment of bridge wire is equal to the unplugged resistance 

 and the rest of the bridge wire. The adjustable resistance consists 

 of manganin coils whose true resistances are accurately known. 



The plugs and their contacts were cleaned with emery paper, and 

 thoroughly tested to insure good contact. All connections were soldered. 

 In taking readings,^the position of the bridge wire contact was read 



(3a) 



IG. 



by a vernier to 0-001 cm. On a suitable scale was made to fall a spot 

 of light from a Nernst lamp by a lens and reflected by the galvanometer 

 mirror. This indicated the movements of the galvanometer needle. 

 The values of a deflection of one scale division in terms of the bridge 

 wire, and of unit change of the bridge wire contact in ohms were obtained 

 Thermo-electric effects were eliminated by reversing the current through 

 the entire bridge. Exact balance points were obtained by interpolation 

 from galvanometer deflections when contact was made at the two 

 adjacent millimetre marks. 



To obtain the fundamental interval of a thermometer, its resistance 

 was measured first in a melting ice mixture and then in a hypsometer. 



