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- 

 gibiHty 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 eight hundred billions of vibrations in one second, 

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

 mer of these numbers, the temperature is 977 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 



