338 Natural Connective Cooling of Wires. 



gases may be compared . He studied the cooling of 0* 1 106 cm . 

 wire, using a cylindrical water-cooled enclosure. Values 

 have been plotted on the graph of fig. 1 instead of on a 

 separate graph. The radiation correction is not large and in 

 its calculation the enclosure temperature has been taken as 

 300° absolute. E, F, and G refer respectively to air, 

 hydrogen, and oxygen. The point for the case of 1/10 atmo- 

 sphere and 900° C. temperature excess is seen to lie rather 

 high for each of the gases considered. 



(5) Conclusion. 



The curve of fig. 1 shows that very diverse data give 

 points which, in general, all lie on one line independent of 

 the size and temperature excess of the object, and of the 

 nature and pressure of the gas involved. It therefore appears 

 that the hydrodynamical theory of convection represented 

 by our formulae is substantially satisfactory even in the case 

 of hot thin wires, provided allowance * is made for the 

 temperature change of the properties of the fluid, an allow- 

 ance brought into prominence by the high temperatures to 

 which wires are usually heated in convection experiments. 

 High temperatures are also used in experiments on forced 

 convection fiom wires, and it is desirable to notice that in 

 this case approximate agreement with the appropriate formula 

 is found even without allowing for the temperature variations 

 of the properties of the fluid, but that agreement is improved 

 when such allowance is made f. 



Langmuir developed a theory of convection in which 

 bodies are considered to be surrounded by a film of gas 

 through which the heat is transmitted by pure conduction, 

 and with certain assumptions, and allowing for the tempe- 

 rature change of the conductivity of the gas, he obtained 

 results in agreement with experiment for free convection. 

 However, he concludes that " for forced convection the film 

 theory does not seem to apply" J. 



It may be counted a superiority of the hydrodynamical 

 theory that the treatment which reconciles theory with 

 experiment for free convection is satisfactory for forced 

 convection also. 



Besides testing the hydrodynamical theory, fig. 1 effects 

 a graphical correlation of diverse convection data for various 

 gases and gas pressures over a wide range of wire diameter 



* Only approximate allowance is made in this paper. 



t Davis, Phil. Mag. xli. p. 899 (1921). 



X Langmuir, Trans. Am. Electrochem. Soc. xxiii. p. 329 (1913). 



