MEMOIR II.] SPECTRUM ANALYSIS OF FLAMES. 5f 



solid burning at different temperatures; proving that as 

 the temperature rises the more refrangible rays appear. 



I took from the fire a piece of burning anthracite coal 

 the fuel ordinarily used in domestic economy in New 

 York and which from its compactness, the intense heat 

 it evolves, and other properties, appears to be well fitted 

 for these investigations. This coal was placed on a 

 support so as to present a plane surface to the slit in 

 the metal screen. The rays coming from it and passing 

 the slit were received on the flint-glass prism, and viewed 

 through the telescope. 



When the coal was first taken from the fire, and was 

 burning very intensely, on looking through the telescope 

 all the colored rays of the spectrum were seen in their 

 proper order. I had previously passed through the slit 

 a beam of sunlight reflected from a mirror, so as to have 

 a reference spectrum with fixed lines. Now when the 

 coal was burning at its utmost vigor, the spectrum it 

 gave did not seem to differ, either as respects length or 

 the distribution of its colors, from the spectrum of sun- 

 light ; but as the combustion declined and the coal 

 burned less brightly, its spectrum became less and less, 

 the shortening taking place first at the more refrangible 

 extremity, one ray after another disappearing in due 

 succession. First the violet became extinct, then the 

 indigo, then the blue, then the green, until at last the 

 red, with an ash-gray light occupying the place of the 

 yellow, was alone visible, and presently this also went 

 out. 



From numerous experiments of this kind, I conclude 

 that there is a connection between the refrangibility of the 

 light which a burning body yields and the intensity of the 

 chemical action going on, and that the refrangibility al- 

 ways increases as the chemical action increases. It might, 

 perhaps, be objected that, in the form of experiment here 



