MI.M..IK XXVIII.] DISTRIBUTION OF HEAT IN THE SPECTRUM. 333 



MEMOIR XXVIII. 



ON THE DISTRIBUTION OF HEAT IN THE SPECTRUM. 



From the American Journal of Science and Arts for 1872, Third Series, Vol. CIV., 

 No. 1G1 ; Philosophical Magazine, August, 1872. 



CONTENTS : Early experiments seeming to prove that the maximum of 

 heat is in the less refrangible spaces. Comparison of the dispersion 

 and diffraction spectra. Effect of compression in the less refrangible 

 regions and of dilatation in the more refrangible. Measure of heat in 

 the two halves of the visible dispersion spectrum. Description of the 

 apparatus employed. The different colored spaces are equally warm. 



MANY experimenters, at various times, have occupied 

 themselves with the problem of the Distribution of Heat 

 in the Spectrum. At first it was supposed that there is 

 a coincidence between the luminous and calorific radia- 

 tions, and that the maximum of intensity in both occurs 

 at the same point that is, in the yellow space. This 

 view was abandoned on the publication of the well- 

 known experiments of Sir W. Herschel, who showed that 

 in certain cases the maximum is below the red. Subse- 

 quently Melloni, having discovered the singular heat- 

 transparency of rock-salt, proved that when a prism of 

 that substance is used, the maximum in question is as far 

 below the red as the red is below the yellow ; but that if 

 the light has passed through flint-glass, the maximum ap- 

 proaches the red; if through crown-glass, it passes into 

 the red ; if through water or alcohol, it enters the yellow. 



In the case of the sun's spectrum the distribution of 

 heat was more closely examined by Professor Miiller, 

 whose results in a general manner confirmed the views 

 then held, that the invisible radiation below the red 



