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Fig. 3. Fig. 4. 



off at the ends of the wire, a calibration is 

 required. For this purpose the pressure was determ- 

 ined by means of tiie set of pipettes referred to 

 before. The loss of heat is measured as follows. 

 The wire forms one of the arms of a Wheatstone 

 bridge (fig. 4) ; the corresponding arm has a resist- 

 ance approximately equal to that of the wire, when 

 it is heated to the definite temperature, which has 

 been chosen with a view to the sensibility (in our 

 case 86 degrees above 20° C.) : it is kept at 

 this temperature by regulating the main current. 

 The two other arms have equal resistance (chosen 

 in connection with the galvanometer resistance). 

 The P. D. at the ends of a portion of one of these 

 resistances is measured with a potentiometer free of 

 thermo-effects : this gives the necessary data for the 

 computation of the loss of heat. 



The calibration was carried out with the set of 

 pipettes mentioned above. Fig. 5 gives the two 



Proceedings Royal Acad. Amsterdam. Vol. XVI. 



