Current of Air flowing past heated Platinum Wires. 247 



class after the first mav be regarded as affording a transition 

 between successive classes or wires. 



With regard to (1) above, Table II. gives the maximum 

 rise in temperature, and the maximum temperature attained 

 by each wire in the case of the present series of wires. 



Table II. 



Wire No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 

 Maxim una in- ] 



crease of tern- 12 28 52 91 120 120 125 130 166 198 



perature. (°C.) J 

 Maximum tern- ) 



perature at- \ 560 6S6 718 740 786 810 825 788 802 801 724 



tained. (°C.)J 



It is seen that the maximum increments of temperature 

 are by no means small, attaining values equal to about 200°C. 

 in the case of the later members of the sequence of wires. 

 This fact is of some little consequence in connexion with the 

 use of electrical heating coils of fine wire for the purpose 

 of heating a stream of air or other gas. Contrary to what 

 might be anticipated, it is easily possible for the temperature 

 of the coil, in the absence of an impressed flow, to be such 

 that actual fusion of one or more turns of the coil occurs 

 when a slow stream of air or other gas is established past the 

 coil. In the case of the wires employed in the present series 

 ol experiments, the highest temperature is attained by No. 7. 



The various peculiarities — see (1) to (5) above — of the 

 thermal effects experienced by the respective wires can be 

 readily discussed in the light of the characteristics of the 

 heat transfer by convection, etc., to which attention has been 

 directed in a previous paper*. Owing, however, to the 

 multiplicity of wires employed in the present instance, such 

 a mode of presentation could afford, at best, but a hazy 

 mental picture of the phenomena appropriate to the present 

 case. The following alternative graphical method of pre- 

 sentation, while possessing no claims to quantitative ac- 

 curacy, has been found of value in the discussion of the 

 heat transference occurring in the present and similar 

 instances : — 



In fig. 4 the several wires of the system are denoted by 

 A, B, C, D, E, F, G, H, I, K, L. The full lines extending 

 into the region above the respective wires represent the 

 heated convection currents arising therefrom. The broken 

 lines in the region below the several wires represent the 

 comparatively colder convection currents ascending towards 



* Proc. Phys. Soc. vol. xxxii. pp. 199-206 (1920). 



