Directional Hot-Wire Anemometer, 



u"51 



are as follows: — With the wires mounted horizon tally, 

 there is, with increasing impressed velocity of air-stream, 

 a comparatively large increase in the resistance of the 

 second wire. The resistance of the first wire meanwhile 

 initially falls off comparatively slowly. On the other hand. 



0225 



10 20 30 



VELOCITY (cms per. sec. Volumes reducf.o to 0°C & 760M.M.) 



with the wires mounted vertically, with increasing velocity 

 of the air-stream, the initial increase of the resistance of 

 the second wire is comparatively small, while there is a 

 very considerable decrease in the resistance of the first 

 wire. The sensitivity of the arrangement employing hori- 

 zontal wires is due, therefore, principally to the increase 

 in the resistance of the second wire, whereas that of the 

 arrangement employing vertical wires originates principally 

 iii the decreased resistance of the first wire. The greater 

 initial sensitivity of the latter arrangement is now readily 



2 U 2 



