HEAT FROM SMALL CYLINDERS IN A STREAM OF FLUID. 
401 
and is found to agree with the determinations of Langmuir ( 41 ) obtained by a 
somewhat different calculation. The value of the radiation loss E = 2 irae per unit 
length is plotted against the temperature, and from this curve the radiation loss for 
any wire may be easily determined at any temperature. The values of the radiation 
losses thus obtained are set down in Table "VI. under the constants C and the true 
convection loss C tf = C —E obtained by subtraction. For each wire the ratio 
C 0 / (0—0 o ) is determined over the range of temperatures and is plotted against 6 — 6 0 . 
The result shows very approximately a straight line whose constants are determined 
from the position of the line of closest fit in the manner already described. In this 
way the constants in the formula 
c o = yo(e-0o)[i+c(e-e o )]. (72 ) 
were obtained for each wire. The constant y 0 is very nearly independent of the 
diameter of the wire as we should expect from the theoretical discussion of Part I. 
By plotting its value against the radius we find approximately 
y 0 = 2-50xl0- 4 (l + 70«).(73) 
expressed in watts. According to the theoretical development we should expect the 
relation C o = k o ( 0—0 o ). Taking k 0 = 5‘66 x 10 -5 calories = 2'37 x 10 -4 watts, this 
result is in surprisingly good agreement with the value of y 0 given in (73), when the 
uncertainty of the exact correction for radiation is taken into account.( 42 ) The slight 
dependence of y 0 on the radius of the wire is probably due to the effect of viscosity. 
The coefficient c is seen to vary remarkably little from the mean value c — 0'00114, 
and may be considered to represent in large measure the variation of the heat- 
conductivity with the temperature. ( 43 ) 
( 41 ) Langmuir, “ Convection and Conduction of Heat in Gases,” ‘ Phys. Rev.,’ 34, p. 415, 1912. 
( 42 ) The success of the theoretical formula (33),, 
H = k 9 q + 2 \/ ttkoso , V-(9 0 ,.(i) 
in representing experimental results leads to a possibility worth future investigation as to whether the 
convection method may not be used in the determination of the heat-conductivity and specific heat of 
gases as a method of continuous flow. By making the temperature difference 9 in (i.) small and intro¬ 
ducing refinements in the methods of measurement, the procedure of the present experiment is especially 
well adapted to the study of the variation of the conductivity and specific heat of gases over an extremely 
wide range of temperature and pressure. A slight modification of the disposition of the apparatus would 
enable the viscosity of the same specimen of gas to be measured under the same conditions, an experi¬ 
mental procedure of the greatest importance in the interpretation of these results according to the kinetic 
theory of gases (see Chapman, “ The Kinetic Theory of a Gas Constituted of Spherically Symmetrical 
Molecules,” ‘ Phil. Trans.,’ A 482, vol. 211, pp. 462-476). 
( 43 ) It is interesting to note that Winklemann gives a temperature coefficient 0 - 00190 for the variation 
of thermal conductivity with temperature (see the ‘ Smithsonian Physical Tables,’ 1910, p. 200). 
3 F 
VOL. CCXIV.—'A. 
