by Chemical Action. 103 



established by the high temperature. Such circumstances 

 compHcate the result ; and it is only by observing the burning 

 of an elementary solid, in which most of these disturbances 

 are cut off, that we can hope to effect a proper resolution of 

 the problem. 



II. Prismatic analysis of the light of an elementaty solid burn- 

 ing at different temperatures ; proving that as the tempera- 

 ture rises the more refrangible rays appear. 



I took from the fire a mass of anthracite coal, the fuel or- 

 dinarily used in domestic CEConomy in New York, and which 

 from its compactness, the intense heat it evolves, and other 

 properties, appears to be well-fitted ibr such investigations as 

 the present. This coal was placed on a support, so as to pre- 

 sent a plane surface to the slit in the metal screen. The rays 

 coming from it and passing the slit were received on a flint- 

 glass prism, and viewed through the telescope. 



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

 ing very intensely, on looking through the telescope I saw all 

 the coloured rays of the spectrum in their proper order. I 

 had previously passed through the slit a beam of sunlight re- 

 flected from a mirror, that I might have a standard spectrum 

 with fixed lines. Now when the coal was burning at its utmost 

 vigour, the spectrum it gave did not seem to me to differ either 

 as respects length or the distribution of its colours from the 

 spectrum of sunlight; but as the combustion declined, and 

 the coal burnt less brightly, I saw that its spectrum was be- 

 coming less and less, the shortening taking place 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 sort, I conclude that 

 there is a connexion between the refrangibiliiy of the light which 

 a Imrning body yields, and the inte?isity of the chemical action 

 goitig on : and that the refrangibility always inc7-eases as the 

 chemical action increases. It may perhaps be objected by some, 

 that, in the form of experiment here introduced, two totally 

 different things are confounded; and that the burning coal 

 not only gives forth its rays as a combustible body, strictly 

 speaking, but also as an incandescent mass. 



'J'o avoid this objection as far as possible, and also to 

 reach a much higher temperature than could have been other- 

 wise obtained, I threw a stream ot oxygen gas on that portion 

 of the antlnacite wliich was opposite the slit; but my expec- 



