388 Mr. W. Sutherland on Thermal 



The temperatures 6 2 and 6 l are determined by the flow 

 of heat from the thin metal wall of the hot jacket to that 

 of the cold one, by conduction along the rubber walls of the 

 cylinder, by radiation across the two gas-chambers, by con- 

 vection-currents in the gas-chambers, and also by conduction 

 through the gas of the chambers, but the conductivity of 

 gases is so small compared to that of even badly- conducting 

 solids, that the direct effect of gaseous conduction may be 

 neglected, although the indirect effect of the conductivity of 

 the gas in determining the amount of heat carried by con- 

 vection may be appreciable, as would appear to be the case 

 with hydrogen and meerschaum plate II. It would be 

 possible to make a rough calculation as to what 2 and 6 X 

 ought to be according to the theory of conduction, but Rey- 

 nolds states that the condition of the radiating surfaces and 

 the sizes of the chambers were altered during the experi- 

 ments, so that it is not worth while to do more than notice 

 that the values obtained for the temperatures of the faces of 

 the porous plates are consistent in a general way with what 

 we should expect from the temperatures of the jackets, the 

 thickness of the gas in the two chambers which was about 

 5 mm., and the given thicknesses of the plates. 



As to the values of B', which stands for 



6ar (R 2 + R 1 )/7 ?0 (y 2 + v,) 2 ; 



since mv 2 is proportional to 0, and (0 2 * + 0i) 2 is nearly the 

 same in all the experiments, we should expect T>'r) /m* to be 

 constant for different gases with the same plate, and propor- 

 tional to the mean radius of the passages in the plate; thus, 

 using the viscosities as obtainable from Graham's experi- 

 ments in terms of that for oxygen as unity, and the molecular 

 masses in terms of that of hydrogen as 2, we have : — 



H 2 . Air. C0 . 



m . . . 2 28-8 44" 



Vo . . . -44 -90 -755 



which give the following values of 10 5 B'^o/m* : — 



H 2 . Air. C0 2 . 



Meerschaum II. . . . 68 158 137 

 Meerschaum III. ... 56 158 

 Stucco 285 755 



This shows that the values yielded by hydrogen, instead of 

 being equal to those given by air, are between -J and J of 

 them, a discrepancy whose cause will be found immediately; 

 but it is to be noted that while the results for hydrogen 



