142 PROCEEDINGS OF THE AMERICAN ACADEMY 



Investigations ON Light and Heat, made and published wholly or in part with 

 appropriation from the Rumford Fund. 



XI. 



DISTRIBUTION OF HEAT IN THE SPECTRA OF 

 VARIOUS SOURCES OF RADIATION. 



By Wm. W. Jacques, Ph.D., 



Fellow of the Johns Hopkins University. 

 Presented April 9, 1879. 



The following research has had for its object a study of the distri- 

 bution of heat in the spectra of a variety of substances, each heated 

 to various temperatures. 



Experiments upon the distribution of heat in the sun's spectrum 

 have already been made by a large number of experimenters, and a 

 few have measured the heat from some terrestrial sources. The former 

 class have failed to give us much scientific information, both because 

 we know so little about our source of radiation, and because we are 

 so little able to estimate the absorbing effect of our atmosphere upon 

 the rays that are given out. The latter class have been too limited, 

 and they are too little comparable with each other. In all of them 

 there may be detected very considerable errors. In fact, the experi- 

 ments that have thus far been made have hardly more than served to 

 guide us in selecting the best methods and apparatus for further 

 research, and to point out the more important sources of error. 



In this research the author has made use of such results as the vari- 

 ous experimenters upon the distribution of heat in the spectrum, from 

 the time of Sir W. Herschel down to the present day, have obtained ; 

 and, profiting by them, has attempted to advance the method one step 

 further, and to determine some relations between the quantitative 

 structure of various substances and the distribution of energy in 

 their spectra, as well as the effects of varying temperature, of lique- 

 faction, and of chemical change of a source of radiation, upon the 

 kind of rays it gives out. 



