Disintegration of Metals at High Temperatures. 273 



O0013 inch diam. The two thermocouple wires do not lie 

 across the wire "W exactly at right angles to its axis, and as 

 the drop o£ potential in the wire W is considerable there is 

 an E.M.F. introduced between the thermocouple wires on 

 this account. Consequently direct current was not used ; 

 the wire was heated by the current developed from an 

 alternator and transformer set. 



Eur. 1. 



xn 



WATER 

 PUMP 



Immediately after a set of observations, an alternative 

 thermocouple of the same wires, and on a circuit of the same 

 total resistance, was calibrated at the temperatures of boiling- 

 water, oil at different temperatures, boiling mercury, melting 

 Na 2 S0 4 and K 2 S0 4 and melting platinum. In order to 

 prevent slight variations of the temperature of the wire "W, 

 the resistances in series with it were immersed in oil ; this 

 was found to work very satisfactorily ; the temperature 

 could be adjusted with considerable accuracy and remained 

 constant. 



On their way to the expansion chamber, the nuclei passed 

 through the annular space, 2 mm. w T ide, between two brass- 

 tubes E, insulated from one another, the outer one earthed 

 and the inner one at —230 volts. The nuclei were tested 

 with the field on and off, and with the tubes E present and 

 absent; it was never found, however, that the tubes required 

 to be removed, as they offered no mechanical difficulty to. 

 the passage of the nuclei. • . 



