398 



MR. W. T. DAVID ON THE RADIATION IN 



totally reflecting (Curves A) to that when they are totally black (Curves D) both for 

 the quartz and the fluorite windows. 



The ratios of the intrinsic radiance when the walls are reflecting to that when they 

 are black, given in this table, are very much the same as those in the fourth column 

 of Table X., which gives the ratio of the emission when the walls are reflecting to 

 that when they are black, measured with the bolometer close up to the quartz plate. 

 In the latter case, however, the ratios are slightly greater. This is because the 

 intrinsic radiance from the gas when enclosed in reflecting walls comes only from an 

 effective length of 59 cm., while the radiation measured when the bolometer is close 

 up to the plate of quartz must be looked upon as coming from a mass of gas of very 

 great dimensions, which would have been infinite had the walls been perfectly 

 reflecting and the ratio of the area of the black bolometer holder and bolometer to 

 that of the total interior surface of the vessel* very small. 



In fig. 15 are shown curves giving the intrinsic radiance from 59 cm. (Curve E) and 

 from 30 cm. (Curve F) of the hot gas after explosions of 13-per-cent. mixtures of 



10 



9 

 8 



'2300 



HHOO 2100 

 ffas 



'900 



(700 



/SCO 



/SCO 



Fig. 15. 



coal-gas and air in the vessel when the walls were black. The fluorite window was 

 used in these experiments and, as in the case of those with 15-per-cent. mixtures, an 

 allowance of 5 per cent, has been made for the absorption of the fluorite and 5 per 



* The ratio of the area of the black bolometer and holder to that of the total interior surface of the 

 vessel was about 1 to 60 in these experiments. 



