Current of Air flowing past heated Platinum Wires. 253 



respective changes o£ temperature of wires Nos. 1, 2, 3, and 

 4 would be approximately - 184°, - 128°, -72°, and -4° re- 

 spectively. Thus, while wires 1 and 2 would differ in tem- 

 perature by d6°, the mean temperature of wires 1 and 2 

 would differ from the mean of the temperature of wires 

 3 and 4 by 118°. The increased sensitivity of the device 

 employing two wires in each arm above that to be antici- 

 pated from a mere doubling of the effective resistance, is 

 attributable to an increase of this nature in the effective tem- 

 perature difference between the pairs of wires. The increased 

 sensitivities of the arrangements when three, four, and five 

 wires are introduced into the respective arms are similarly 



300 350 400 

 DEFLECTION 



explained. Analogous results were obtained when the whole 

 series of wires were heated. The sensitivities in these cases 

 were, however, slightly different from those indicated by 

 fig. 6, but the relative sensitivities were of the same order as 

 those just discussed. In the region of very low impressed 



