Constant Current Type of Hot-Wire Anemometer. 723 



the bridge current being maintained constant meanwhile. 

 The air stream was derived from a 5 cubic feet gas holder, 

 and was controlled and its velocity determined in the manner 

 detailed in previous papers. The results obtained employ- 

 ing values of the bridge current ranging from 0*9 amp. to 

 1*5 amp. are shown in fig. 3. The main features of the 

 calibration curves are briefly as follows : — With gradual 

 increase of the impressed stream from zero, the initial 

 comparatively large rotation necessary to restore balance of 

 the bridge is succeeded by a region of velocities for which 

 the necessary rotation increases but slowly with increase in 



12 3 4 5 



VELOCITY(CMS.PERSEC,VOLUMES REDUCED TO O'c AND 760 KM.) 



the magnitude of the impressed velocity. With subsequent 

 increase of the impressed velocity the necessary rotation 

 increases extremely rapidly. These characteristics of the 

 calibration curves are readily interpreted by reference to the 

 inclination-resistance curves of fig. 2. It is seen that with 

 continuous increase of the inclination of the wire to the 

 horizontal, the resistance of the wire initially increases 

 extremely slowly. With further rotation, the resistance 

 increases comparatively rapidly until inclinations approaching 

 the vertical are reached, when the rate of variation of 

 resistance with inclination again becomes very small. The 

 velocity-inclination curves (fig. 3) for inclinations of the 



