70 SPECTRUM ANALYSIS OF FLAMES. [MEMOIR II. 



of combustion, steam and carbonic acid, mingled with 

 atmospheric air, constitute the oxidizing flame, which 

 envelops the blue cone, and emits Brewster's mono- 

 chromatic yellow light. That the yellow light comes 

 from this flame is proved by the greater length of its 

 image. 



VII. Physical cause of the production of light by chem- 

 ical action . 



Do not the various facts here brought forward prove 

 that chemical combinations are attended by a rapid 

 vibratory motion of the particles of the combining 

 bodies, which vibrations become more frequent as the 

 chemical action is more intense? 



The burning particles constituting the inner shell of 

 a flame are executing about four hundred billions of 

 vibrations in one second ; those in the middle about 

 six hundred billions, and those on the exterior, in con- 

 tact with the air, about eight hundred billions in the 

 same time. The quality of the emitted light, as re- 

 spects its color, depending on the frequency with which 

 these vibrations are accomplished, increases in refran- 

 gibility as the energy of the chemical action becomes 

 greater. 



The parts of all material bodies are in a state of 

 incessant vibration ; that which we call temperature de- 

 pends on the frequency and amplitude of these vibra- 

 tions conjointly. If by any process, as by chemical 

 agencies, we increase that frequency to between four 

 and eisfht hundred billions of vibrations in one second, 



O 7 



ignition or combustion results. In the case of the for- 



O 



mer of these numbers, the temperature is 9Y7 Fahr. 

 At this temperature the waves propagated in the ether 

 impress the organ of vision with a red light. This also 

 is the temperature of the innermost shell of a flame. If 



