900 Mr. A. H. Davis on the Heat Loss by 



the form 



H/k=J?(hc/k), (1) 



where 



H = heat lost per second per unit length of the wire, 

 per degree temperature excess above stream 

 temperature. 



& = heat conductivity of the fluid. 



c~ specific heat of the fluid per unit volume. 



v = velocity of the fluid stream. 



1= diameter of the wire. 



It was pointed out that since for a given gas cvjk is 

 constant (v being the kinematical viscosity), the above 

 reduces to 



E.jk = F(vl/v). ...... (2) 



Here vl/v is the familiar variable in hydrodynamics de- 

 termining fluid resistance and turbulence, so the equation in 

 this form involves a relation between the thermal and 

 dynamic effects of a fluid stream. The dj namic effect is 

 represented by the formula 



R/(^/ 2 ) =t\vllv), (3) 



where 11 = fluid resistance per diameter length of the wire, 

 p — density of the fluid. 



The present paper extends the investigation of the agree- 

 ment of the similitude equation with published data for heat 

 loss from cylinders in a stream of air, and determines the 

 relation between the thermal and dynamic effects of the 

 stream in this case. 



Osborne Reynolds *, considering the heating surface of 

 boilers, pointed out that, from the identity of the two 

 molecular phenomena by means of which convection of heat 

 and of momentum (surface friction) were carried on, their 

 dependence on the conditions of motion would be the same. 

 Formulae he deduced for cool liquid flowing through a hot 

 pipe indicate that 



,{ -, * "' I oc Temperature difference between fluid and 



\ unit area / r 



x pipe. 



<x Fluid resistance per unit area. 



oc Reciprocal of the velocity of the fluid in 

 the pipe. 



* Reynolds, Proc. Manchester Lit. & Phil. Soc. 1874. See also 

 Stanton, Eeport Adv. Committee Aeronautics, p. 45 (1912-13). 



