F.XN.I>MI>\S OF COAL-HAS ANI> AII; 



401 



means of the formula 



where 



RX is the intrinsic radiance from x cm. of gas, 



R, is tin- intrinsic radiance from an infinite thickness, and 

 K is the coefficient of absorption per cm. 



The sixth column in this table gives the value of K at various temperatures, and 

 the last column gives the value K would have were the gas expanded down to 

 atmospheric pressure, assuming, of course, that the transparency of a thickness of 

 gas inversely proportional to the gas pressure is independent of the pressure.* 



TABLE XV. 15-per-cent. Mixtures of Coal-gas and Air. Walls black. 



Fluorite Window. 



The close agreement between the observed and calculated values shows that the 

 exponential law of absorption is closely obeyed in the gaseous mixture during cooling. 



Table XVI. gives the values which the intrinsic radiance from 1 cm. would have 

 were the gaseous mixture perfectly transparent. The intrinsic radiance corrected for 

 absorption from 1 cm. of the gaseous mixture is the limit of R X /J? when x = in the 

 formula R, = R(l <T Kx ) ; this is equal to KR,.. The fourth column gives the ratio 

 of the intrinsic radiance corrected for absorption when the walls are reflecting to that 

 when they are black. The figures in the last column an; proportional to the radiation 



VOL. CCXI. A. 



* See, however, p. 404. 

 3 F 



