298 Mr. Dugald Clerk [Jan. 29, 



great accuracy in the determination Ijotli of mixture used and 

 temperatures attained. 



By these experiments more accurate knowledge is now available 

 of the actual temperatures and temperature distribution in gaseous 

 explosions, both in closed vessels and in engines. The knowledge 

 of temperatures has enabled specific heat determinations to be made, 

 and also heat flow determinations, by various methods which need not 

 be here described. Knowledge as to heat flow and the conditions of 

 its variation is accumulating, and further determinations of specific 

 heat of different gases are necessary. Work of this nature is in 

 progress by Members of the Committee, and engines are being 

 designed to be fitted up in the Engineering Laboratory of the 

 Imperial College of Science and Technology for the purpose of 

 continuing the experiments in a more systematic and sustained 

 manner. The Avork is very laborious, and has necessitated the design 

 and invention of many new instruments. Optical indicators have 

 been much improved by the w^ork of the Committee ; but details 

 of this w^ork must be reserved for a future occasion. 



The work of Callendar and Hopkinson, with David, his pupil, on 

 radiation from gaseous explosions is, how^ever, of very high interest, 

 and this address may be concluded with a short description of their 

 results. 



Prof. Callendar's experiments were made to determine the pro- 

 portion of radiation from a Bunsen flame to the total heat of 

 combustion. The particular Bunsen used was of the Meker type. 

 It had a nickel grid of three centimeters in diameter, and consumed 

 gas at the rate of 0'185 cubic feet per minute. In burning in the 

 air the total heat of combustion was disposed of in two ways — first, 

 the heat radiating from the flame, w^hich passed at the velocity of 

 light through the surrounding atmosphere ; and, second, the heat 

 ultimately lost from the flame by mixture of the hot gases wdth the 

 atmospheric air of the room. The ratio of air to gas by volume was 

 determined, and experiments were made in which that ratio varied 

 from five to one, and finally air was cut off entirely. The air-gas ratio 

 was that of the mixture entering the burner, and made no allowance 

 for air drawn in by the flame, so that the actual mixture radiating 

 would contain more air than the figures given. It was found that as 



the value diminished the radiation increased down to — =2*5. 



gas 



At 1 • 5 the radiation again diminished, remained practically constant 



at one, and when air was entirely cut off and nothing but a luminous 



flame was burning it again rose. The following figures show this 



very clearly : — 



Total radiation p.c. 10-5 12*3 14*0 15*0 14-1 14-6 17*0 



Ratio — by volume 5 4 3 2-5 1'5 1 



gas -^ 



With the proportion of five air to one of gas by volume, together 



