491 Origin of Radiation in a Gaseous Explosion. 



The energy in the radiation of shorter wave-length (which 

 includes the luminous radiation) is small, and an analysis of 

 the radiation emitted indicated that the emission of such 

 radiation takes place only during explosion and in the very 

 early stages of cooling*. It is probable, therefore, that the 

 emission of the short wave-length radiation is dependent 

 upon chemical activity. 



6. This, together with the fact that the very large emission 

 of radiation during the explosion period (i. e. the period 

 between ignition of the gaseous mixture and the attainment 

 of maximum pressure) is partly independent of temperature f, 

 leads the writer to believe that the energy of chemical com- 

 bination passes partly into the form of both high and low 

 frequency vibrations of the internal parts of the combining 

 molecules. Various considerations based partly on his expe- 

 rimental work and partly upon Jeans's theory J lead to the vieu 

 that the energy in the high-frequency vibrations is damped 

 wholly by the emission of radiation, while that in the low- 

 frequency vibrations (corresponding to radiation of wave- 

 length 2fju and over) is damped partly by emitting radiation 

 and partly (and mainly) by a transference during molecular 

 collisions from it to the other forms of molecular energy 

 (translational and rotational). In the case of the high- 

 frequency vibrations the damping proceeds until the energy 

 in them is reduced to zero; but in the case of the low- 

 frequency vibrations the energy will only be reduced to an 

 equilibrium value (which depends mainly on the gas tem- 

 perature) § . After this value has been reached the energy 

 which they lose by radiation will tend to be restored to them 

 during collisions. 



* David, Phil. Trans. A. vol. ccxi. p. 390. 



t David, Phil. Trans. A. vol. ccxi. p. 381. 



X See his ' Dynamical Theory of Gases,' Camb. Univ. Press, 1904, 

 chap. ix. 



§ In this connexion see theory suggested in Phil. Mag. Feb. 1913, 

 -p. 267. 



