Amount of Radiation emitted by a Gas Flame. 



55 



" Some Observations on the Amount of Luminous and Non- 

 luminous Radiation emitted by a Gas Flame." By Sir John 

 Conroy, Bart, M.A., Bedford Lecturer of Balliol College 

 and Millard Lecturer of Trinity College, Oxford. Com- 

 municated by A. G. Vernon Harcourt, LL.D., F.R.S. 

 Received November 11. Read December 19, 1889. 



In 1863 Julius Thomsen communicated to the " Naturforscher- 

 versammlung " at Stockholm an account of some determinations he had 

 made of "The Mechanical Equivalent of Light," and an abstract of 

 this paper appeared in ' Poggendorff 's Annalen ' (vol. 125, 1865, 

 p. 348). 



He allowed the radiation from a sperm candle, a moderator lamp, 

 aud a gas name, to fall on the face of a thermopile, and noted the de- 

 flection of the needle of a galvanometer in the thermoelectric circuit, 

 when the radiation fell directly on the pile, and when it did so after 

 passing through 20 cm. of water contained in a glass cell. In order 

 to reduce the readings to absolute measure, he placed a glass globe 

 containing hot water in front of the thermopile, and observed the 

 deflection of the galvanometer ; the mass of water contained in the 

 globe, the water- equivalent of the globe, the temperature of the water, 

 and of the room, being all known, from the observed rate of cooling 

 the radiation, calculated by Dulong's formula, was determined. 



By assuming that the 20 cm. of water absorbed all, or nearly all, 

 the heat rays {i.e., the non-visible), and transmitted nearly all the 

 light rays, the loss of light being found experimentally to be only 13 

 per cent., he was able to calculate the proportion of light and heat 

 (i.e., visible and non-visible) radiations emitted by the flames, and to 

 determine the mechanical equivalent of the light. He found that the 

 ratio of the luminous to the total radiation was about the same for 

 the candle, the oil lamp, and the gas flame, the amount being nearly 

 2 per cent. 



He states " a flame whose light intensity is equal to one light unit, 

 that is, one due to the combustion of 8'2 grams of spermaceti per hour, 

 radiates as light per minute an amount of heat which would raise the 

 temperature of 41 grams of water one degree." On this last sen- 

 tence it must be remarked that a light unit cannot be expressed by a 

 statement of the mass of a combustible consumed, but perhaps the 

 original paper contains qualifications omitted in the Abstract. 



Melloni (' Comptes Rendus,' vol. 31, 1850, p. 476) states 44 Le rayon- 

 nement de la flarame d'huile contient 90 parties sur 100 de cefcte 

 espece de chaleur (i.e., chaleur obscure), le rayonnement du platine 



