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LIV. 0?i the Production of Light hy Heat. Bij John 

 William Drapeii, M.D., Professor of Chemistry in the 

 University of New York*. 



ALTHOUGH the phaenomenon of the production of light 

 by all solid bodies, when their temperature is raised to a 

 certain degree, is one of the most familiar in chemistry, no 

 person so far as I know has hitherto attempted a critical in- 

 vestigation of it. The difficulties environing the inquiry are 

 so great, that even among the most eminent philosophers a 

 diversity of opinion has prevailed respecting some of the lead- 

 ing facts. Thus Sir Isaac Newton fixed the temperature at 

 which bodies become self-luminous at 635°, Sir Humphry 

 Davy at 812°, Mr. Wedgwood at 947°, and Mr. Daniell at 

 980°. As respects the nature of the light emitted there are 

 similar contradictions. In some philosophical works of con- 

 siderable repute, it is stated that when a solid begins to shine 

 it first emits red and then white rays ; in others it is asserted 

 that a mixture of blue and red light is the first that appears. 

 I have succeeded in escaping or overcoming many of the 

 difficulties of this problem, and have arrived at satisfactory 

 solutions of the main points; and as the experiments now to 

 be described lead to some striking and perhaps unexpected 

 analogies between light and heat, they commend themselves 

 to our attention as having a bearing on the question of the 

 identity of those imponderable principles. It is known that 

 heretofore I have been led to believe in the existence of car- 

 dinal distinctions, not only between these but also other im- 

 ponderable agents ; and I may therefore state, that when this 

 investigation was first undertaken, it was in the expectation 

 that it would lead to results very different from those which 

 have actually arisen. 



The following are the points on which I propose to treat: — 



1. To determine the point of incandescence of platinum, 

 and to prove that different bodies become red-hot at the same 

 temperature. 



2. To determine the colour of tlie rays emitted by self- 

 luminous bodies at different temperatures. This is done by 

 the only reliable method — analysis by the prism. 



From these experiments it will appear, tiiat as the tempe- 

 rature rises the light increases in refrangibiiity ; and making 

 a due allowance lor the physiological imperfection of the lye, 

 tiie true order of the colours is red, orange, yellow, green, 

 blue, indigo, violet. 



* Coiuinuiiicatcl liy the Author. 



