70 Major W. T. David on the Calculation of 



E — differential coefficient of E with respect to t y 

 i. e. the rate at which the walls receive radia- 

 tion per sq. cm. of surface (AF). 



E max . — the maximum rate at which the walls receive 

 radiation per sq. cm. of surface (HGr). This 

 takes place during the explosion period. 



E 2 — total radiation at time t received by the bolometer 

 per sq. cm. of its surface from a cone of gaseous 

 mixture of unit solid angle (AE, when bolo- 

 meter is some distance away from rluorite 

 window). 



E;t — final value of E x , i. e. the value of E* registered 

 after a time when the gaseous mixture has 

 cooled to such an extent that it emits no 

 further radiation (KJ). For all practical pur- 

 poses this is the value of Ej registered at 

 1 second after ignition. 



Ei — differential coefficient of E* with respect to t. 

 This is the intrinsic radiance (AF). 



Rimax, — the maximum value of E x which occurs during 

 the explosion period (HG). 



The Maximum Eate of Emission of Eadiation during 

 Explosion. 



(a) Cylindrical Explosion Vessel 30 cm. diameter and 

 30 cm. long. 



6. It has previously been shown * that the rate at which 

 the gaseous mixture emits radiation is a maximum some little 

 time before the attainment of maximum pressure. From an 

 examination of a large number of films it would appear that 

 the maximum rate of emission occurs at or near the second 

 point of inflexion in the pressure curve during the explosion 

 period. The curves in fig. 3 have been taken from three 

 typical films. The A curves relate to a 10*5 per cent., 

 mixture of coal-gas and air at atmospheric density ; the 

 B curves to a 10*2 per cent, mixture at 1*24 atmospheres 

 density ; and the C curves to a 9'2 per cent, mixture at 

 1*37 atmospheres density 7 t« The dotted curves are the dif- 

 ferentials of the radiation curves, and they show clearly that 

 the maximum rate of emission occurs near the time when the 

 gas-pressure or temperature curves undergo their second 



* Phil. Trans. A. vol. ccxi. p. 381. 



t All the gaseous mixtures referred to in this paper were originally at 

 atmospheric temperature. 



