244 Dr. J. S. Gr. Thomas on Thermal Effect of a slow 



air-flow is most readily made by determining in each case 

 the change of temperature of the individual wires accom- 

 panying the establishment o£ the air-flow in the tube. The 

 results given in figs. 2 and 3 indicate how the temperatures 



o 10 15 zo 



VELOCITY(CMS PER 5EC, VOLUMES REDUCED TO Cf'C t 



25 



>760mh) 



to which the respective wires were raised by the heating 

 current of 1*1 amp. employed depended upon the magnitude 

 o£ the mean velocity of the air-flow established in the tube. 

 The ordinates in every case represent the increase or de- 

 crease of temperature of the wire above or below the normal 

 temperature of the wire in the absence of flow. The curve 

 representing the behaviour of No. 7 wire is omitted from 

 fig. 2 for the sake of clearness. Its descending portion 

 lies between the corresponding portions of the curves 



30 



