532 Mr. J. S. G. Thomas 



on 



velocity of the stream, a the radius of the heated cylinder, 

 #o the temperature of the cylinder above that of the sur- 

 rounding medium at a great distance, or the similar expression 

 deduced by Rayleigh (see footnote on p. 531) is the type 

 of expression most readily applicable to the present series of 

 experiments. Considering the curves for air and carbon 

 dioxide shown-in fig. 17, it may be remarked that the resistance 

 of the exposed wire under zero flow in the respective gases 

 was 0*7906 ohm and 0*7869 ohm, so that the initial temper- 

 ature of the wire in the two cases was very approximately 

 the same. In the cases of oxygen and nitrogen, the initial 

 temperatures were still more nearly equal to that in the case 

 of air. Consider two points P and Q on the respective curves 

 for carbon dioxide and air having the same value of the 

 deflexion. The total heat convected from the wire is made up 

 of that due to free convection from the wire, and that con- 

 vected away by the stream. The respective resistances of the 

 wire corresponding to the deflexion 100 (at this deflexion the 

 proportional effect of free convection is the least in the present 

 sequence of experiments) were 0*541 ohm in air and 0*536 

 ohm in carbon dioxide. The corresponding temperatures of 

 the wire are 358° C. and 352° C. It is therefore legitimate 

 to assume that for corresponding points P and Q on the same 

 ordinate, the heat convection from the wire is very approxi- 

 mately the same in the two cases. The subscript x referring 

 to air, and 2 referring to carbon dioxide, we have for points 

 such as P and Q, 



Hi = H 2 = S(s 1 (r 1 k 1 V 1 a 1 j'ir)^0o 1 — 8(s 2 ar 2 k 2 y '^ji^O^ 



Now, Ql £z0 o2 ; a l = a 2 : and V x and V 2 are proportional to 

 the respective ordinates at P and Q. We have therefore 

 very nearly Si<rik{V l = s 2 <r 2 k 2 V 2i 



k 2 Syct^Vi 

 i.e. 



ki S 2 (T 2 V 2 ' 



Before applying this relation it is essential to refer to the 

 temperatures at which the respective values of s x , a lt s 2 , <r 2 , 



are to be taken. Now the ratio — remains practically 



a 2 



unaltered over the possible range of temperatures employed 

 in these experiments. The equipartition theory requires 



constancy of the ratio -. The ratio remains practically 

 s 2 



the same if values deduced from the quantum hypothesis are 



