248 Dr. J. S. G. Thome s on Thermal Effect of a slow 



the wires. The figure represents the condition o£ affairs in 

 the absence of any impressed now of air in the tube. The 

 lengths of the various full lines are drawn so as to indicate 



Fig. 4. 



t 



iK 



i i 



1 s \ 



1 



i 

 1 

 1 

 » 



roughly the relative temperatures of the respective wires, and 

 consequently of the respective convection currents arising 

 therefrom (see Table I.) . The colder convection currents 

 below the wires are similarly represented by the broken lines, 

 but are somewhat shorter in length, owing to their neces- 

 sarily lower temperature. Fig. 5 represents the altered con- 

 ditions ruling when the heated wires are subjected to the 



Fiff.5. 



influence of an impressed flow of air moving with small 

 velocity. For the sake of simplicity, consider first of all the 

 two wires A and B. It has been shown elsewhere* that the 

 heat-transfer from the first of the two wires A, say, to B, 

 owing to an increasing impressed air-flow, is characterised 

 by two opposing tendencies, viz. (1) the initial decreasing 

 temperature of the resultant convection current, and (2) the 

 decreasing fall in temperature occurring during transfer 

 from the first to the second wire. The resultant thermal 

 * Proc. Pliys. Soc. he. cit. 



