OP ARTS AND SCIENCES. 143 



The experiments have included a measurement of the distribution 

 of heat in the spectrum of a platinum wire, heated to various meas- 

 ured temperatures between a low red and a full white heat, which re- 

 sulted in the discovery that platinum gives a spectrum in which the 

 relative distribution of energy is nearly the same for all temperatures 

 between these limits. 



That is, if we represent the intensities of heat at different parts of 

 the spectrum by ordinates, the curve joining these will have nearly the 

 same geometrical form, and the same position of the maximum, for all 

 temperatures of the wire between these limits. The curve of distribu- 

 tion was then determined at a low red heat, at a bright red, and at 

 a white heat for the black oxide of copper (CuO), the black oxide 

 of iron (Fe 8 4 ), the red oxide of iron (Fe. 2 8 ), the green oxide of 

 chromium (Cr 2 3 ), and the white oxide of aluminium (A1 2 3 ). 



It was found that for each substance the geometrical form of the 

 curve was nearly independent of the temperature, but that it varied 

 somewhat with the different substances. 



A relation between the molecular weights of these substances and 

 the forms of the curves, and also a relation between the colors of the 

 bodies at the ordinary temperatures and the radiations emitted when 

 heated, appeared in a study of their curves. The effect of the passage 

 from the solid to the liquid state was studied in the case of CuO, 

 and it was found that the geometrical form of the curve remained the 

 same. 



The present paper contains a review of the more important ex- 

 periments that have been made upon this subject, and to these there is 

 added an account of the author's own experiments. 



HISTORICAL. 



Previous to the time of Sir Wm. Herschel there had been no really 

 scientific study of the distribution of heat in the spectrum. 



As the results of three very limited and inaccurate series of experi- 

 ments, by Landriani,* Rochon,f and Senebier,i it was supposed that the 

 sun's rays of light were accompanied by rays of heat, which were in 

 general stronger for rays of low than for those of high refrangibility, 

 but which reached their maximum somewhere in the yellow or orange 

 rays. 



* Ann. der Physik, x. 



t Eecueil <Ie Mem. sur la Mec. et Physique, 1783. 



J Mem. Pkysico-chemiques, ii. 74. 



