Heat from a Pair of fine heated W 



ires. 



285 



wire. It will be observed that the value of the impressed 

 velocity at which the respective maxima are attained becomes 

 less as the distance between the wires diminishes. Below 

 such value of the impressed velocity, the behaviour of the 

 thermometer type of hot-wire anemometer is conditioned 

 largely by the relative disposition of the wires both with 

 regard to one another and to the walls of the channel in 

 which the flow occurs. This point is of no little consequence 



VELOCITY ICMS. PER SEC, VOLUMES REDUCED TO 0°C and 760 



in the technical application of this type of hot-wire anemo- 

 meter, as the velocities occurring in gas mains are frequently 

 below those to which reference has just been made. Further 

 consideration of this matter is deferred, however, until the 

 completion of an investigation at present in progress, u sing- 

 three platinum wire grids inserted in the flow tube, the 

 central one functioning as a heating grid between two 

 thermometric grids. 



The values of the maximum increase of resistance of the 

 second wire due to the impressed stream, derived from figs. 2 



