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ME. J. H. BRINKWORTH ON THE SPECIFIC HEAT OF STEAM AT 



into the lower end of the flow-tube. This thermometer sheath reached right up 

 the flow-tube to within a few millimetres of the lower end of the heating coil, 

 so that by moving the thermometer up or down in its sheath, the distance 

 between the end of the heating coil and the middle of the thermometer could be 

 easily varied between wide limits. This thermometer was made by Mr. W. J. 

 COLEBROOK, Superintendent of the Physics Workshop at the Imperial College, 

 and here I desire to record my indebtedness to him for the assistance I have 

 obtained during the construction of the apparatus used in this investigation. 



The Platinum Th.ermometer Bridge and the Measurement of the Fundamental 

 Interval and Stem-exposure of the Thermometer. 



The well-known form of bridge designed by Prof. CALLENBAR was used, the 

 plug contacts being replaced by mercury cups. Three calibrations of the coils and 

 bridge-wire were made during the course of this investigation and corresponding 

 readings in these different calibrations agreed to within 0'005 cm. of bridge-wire. 

 An astatic galvanometer, with a long quartz fibre suspension, was used with the 

 bridge, and the sensitiveness in the final experiments was such that by moving 

 the contact maker 01 cm. on the bridge-wire, an alteration of from 10 to 15 

 divisions in the deflection was produced on reversing the current. Observations 

 of the sensitiveness were made during each experiment, and no attempt was 

 made to adjust the contact to obtain an exact balance. The usual apparatus was 

 employed for the determination of the fixed points, and these were re-determined 

 after every removal of the thermometer from its sheath. A series of observations 

 of the freezing- and boiling-points, with various lengths of the thermometer stem 

 exposed, was made. These values were plotted, and from the curves obtained 

 the variation of the fundamental interval with stem-exposure could be deduced. 

 The values obtained on September 12, 1912, were as follows : 



. These results show that the fundamental interval only falls by about 1 part 

 ' when the stem-exposure is changed from to 16 cm. In the calculations, 



