408 MR. W. T. DAVID ON THE RADIATION IN 



(viii.) Denser mixtures emit radiation much more strongly than thinner mixtures, 

 especially at the moment of maximum pressure and in the initial stages of cooling. 

 The emission varies approximately as the square root of the density. 



Part II. The following results refer to the experiments made in the vessel whose 

 walls were silver-plated and, therefore, could be made reflecting or absorbent at will. 

 The experiments were made with the bolometer placed at some distance behind the 

 plate of fluorite, so that the emission was measured from a cone of gas of small solid 

 angle : 



(ix.) The intrinsic radiance from a gaseous mixture at any given temperature after 

 explosion depends largely on the reflecting power of the interior surface of the 

 explosion vessel, and also on the size of the vessel. The greater the reflecting power, 

 or the greater the size of the vessel, the greater the intrinsic radiance. This effect is 

 probably due both to greater vibratory energy and to greater transparency of the gas 

 in the larger vessels and in the reflecting vessels. 



(x.) (a) Gaseous mixtures after explosions in vessels with reflecting walls are very 

 highly transparent to the radiation which they emit at maximum pressure and 

 throughout cooling. 



(b) Gaseous mixtures after explosion in a vessel with black walls are very highly 

 transparent at the moment of maximum pressure and also in the initial stages of 

 cooling. Later on in the cooling they become fairly opaque. 



[(xi.)-(xiv.) refer to coal-gas mixtures of the same strength but of different 

 densities.] 



(xi.) The ratio of the intrinsic radiance from a definite thickness of gaseous 

 mixtures of the same strength at any given temperature when the walls of the 

 explosion vessel are reflecting to that when the walls are black decreases as the 

 density increases. 



(xii.) When the walls of the explosion vessel are black the transparency of a thick- 

 ness of gas inversely proportional to the density at any given temperature increases 

 as the density decreases. 



(xiii.) (a) The intrinsic radiance from a definite thickness of gaseous mixture at 

 any given temperature after explosion in the vessel with black walls varies as the 

 square root of the density. 



(b) The intrinsic radiance from thicknesses of gas inversely proportional to the 

 density varies as the fourth root of the density. 



(xiv.) The intrinsic radiance corrected for absorption from 1/D cm. of the gaseous 

 mixtures at any given temperature in the vessel with black walls seems to decrease 

 as the density (D) increases. 



(xv.) The radiation (after correcting for absorption) from the hot gaseous mixture 

 after explosion varies with the temperature approximately as PLANCK'S foriliula for a 



