HEAT FROM SMALL CYLINDERS IN A STREAM OF FLUID. 
383 
PAET II. 
Experimental Determination oe the Convection Constants of Small 
Platinum Wires. 
Section 8. Introduction. 
The experimental study of thermal losses from heated bodies under various 
conditions dates back to the classical researches of Dltlong and Petit( 15 ) in 1817 . 
Since that date numerous experiments have been carried out on the radiation and 
convection of heat, most of which fall under two categories :— 
(i.) The study of the total heat losses from a heated body to an enclosure 
maintained at constant temperature and containing different gases under various 
conditions of pressure. In so far as these experiments refer to the heat losses from 
wires, we may cite the classical work of Ayrton and Kilgour( 16 ) and that of 
Petavel.( 17 ) More recently we may quote the experiments of Kennelly( 18 ) on the 
forced convection of heat from small copper wires, and to a series of detailed papers 
recently published by Langmuir( 19 ), where exhaustive references to experiments on 
convection problems are to be found. 
(ii.) The study of radiation losses from heated solids to enclosures maintained at 
constant temperature, in which connection the earliest measurements carried out by 
an electrical method appear to have been due to Bottomley. ( 2a ) In high vacua this 
subject has in recent years been made the field of much research, especially in 
connection with the development of the metallic filament lamp. In the present work 
the heat-loss by radiation plays a very subordinate part and was not made the subject 
of special investigation. 
The measurement of thermal losses in stagnant media, while simpler to carry out 
experimentally, and perhaps more important in practical applications, has thus far 
defied mathematical investigation on a rational physical basis. On the other hand, 
the mathematical interpretation of heat convection as a problem of heat conduction in 
moving media admits of fewer restrictions and leads to the results of Boussinesq( 21 ) 
( 15 ) Dulong et Petit, ‘Ann. de Chimie et de Physique,’ t. 7, 1817. 
( 16 ) Ayrton and Kilgour, “The Thermal Emissivity of Thin Wires in Air,” ‘Phil. Trans.,’ vol. 183, 
Part I., p. 371, 1892. 
(U) Petavel, ‘Phil. Trans.,’ vol. 191, p. 501, 1898; also ‘Phil. Trans.,’ vol. 197, p. 229, 1901. 
( 18 ) Kennelly, Wright, and Van Bylevelt, ‘Trans. A.I.E.E.,’ vol. 26, p. 969, 1907 ; also ‘Trans. 
A.I.E.E.,’ vol. 28, pp. 363-396, 1909. 
( 19 ) Langmuir, ‘Phys. Rev.,’vol. 34, p. 401, 1912; also ‘ Proc. A.I.E.E.,’June, 1912, p. 1011; ‘ Proc. 
A.I.E.E.,’ April, 1913. 
! ( 20 ) Bottomley, ‘Phil. Trans.,’ A, vol, 178, p. 429, 1888; ‘Roy. Soc. Proc.,’ vol. 66, p. 269, 1900, 
( 21 ) Boussinesq, loc . cit ., p. 297. 
