692 Dr. J. S. G. Thomas on 



The mode of experiment was as follows : — A steady flow 

 of dry air was established in the system for about an hour, 

 and the balance of the Oallendar& Griffiths' bridge ascertained 

 in the absence of any current in the heating element. The 

 point of contact on the bridge wire was then moved to the 

 point corresponding to 2 G C. difference between the two 

 thermometers, and the value of the current in the heater 

 adjusted until the bridge balance was restored at the point so 

 determined. The necessary displacement at 15° C. was 2*65 cm. 

 of bridge wire. The bridge current was throughout adjusted 

 to 0*010 amp. On account of the relatively large thermal 

 capacity of the flow system, a considerable time — of the order 

 of 2 to 3 hours when the thermometers were widely separated 

 — elapsed before the system attained a steady condition. 

 Owing to slight inequality of the two thermometer resistances 

 at 0° (J., a slight alteration of balance accompanied a change 

 of atmospheric temperature. Such alteration was taken 

 account of throughout the Observations. The potential drop 

 across the heater was determined as already explained. The 

 velocity of flow in the system was determined as detailed in 

 previous papers. 



The results were plotted in the form of curves in which 

 the abscissae represent velocities of flow, and ordinates the 

 respective supplies of energy to the heater to maintain the 

 second thermometer at a temperature 2° 0. above that of the 

 first. 



Results and Discussion. 



Internal diameter of flow tube 2*01 cm. 



External diameter of flow tube 2'22 cm. 



R of 1st Thermometer (cms. of bridge 



wire) .. 363-40 



Temperature coefficient of 1st Thermo- 

 meter 0*003556 



E of 2nd Thermometer *(cms. of bridge 



wire) 368-75 



Temperature coefficient of 2nd Thermo- 

 meter 0-003552 



Shift of balance for 1° 0. change of atmo- 

 spheric temperature (cm. of bridge 

 wire) 0017 



In fig. 2 are given the forms of the calibration curves 

 obtained when the first thermometer was throughout placed 

 at a distance of 30 cm. from the heating: element while the 



