230 FKAGMENTS OF SCIENCE. 



it is also a powerful absorber. While, therefore, at the 

 present moment it is copiously pouring forth radiant heat 

 itself, it does not allow a single ray from the metal behind 

 to pass through it. The varnish then, and not the metal, is 

 the real radiator. 



Now Melloni, and Masson, and Courtepee, experimented 

 thus : they mixed their powders and precipitates with 

 gum-water, and laid them by means of a brush upon the 

 surfaces of a cube like this. True they saw their red pow- 

 ders red, their white ones white, and their black ones black, 

 but they saw these colors through the coat of varnish 

 which encircled every x>article of their powders. "When, 

 therefore, it was concluded that color had no influence on 

 radiation, no chance had been given to it of asserting its 

 influence ; when it was found that all chemical precipitates 

 radiated alike, it was the radiation from a varnish common 

 to them all which showed the observed constancy. Hun- 

 dreds, perhaps thousands, of experiments on radiant heat 

 have been performed in this way by various inquirers, but 

 I fear the work will have to be done over again. I am not, 

 indeed, acquainted with an instance in which an oversight 

 of so trivial a character has been committed in succession 

 by so many able men, and vitiated so large an amount of 

 otherwise excellent work. 



Basing our reasonings, then, on demonstrated facts, we 

 arrive at the extremely probable conclusion that the envel- 

 ope of the particles, and not the particles themselves, w T as 

 the real radiator in the experiments just referred to. To 

 reason thus, and deduce their more or less probable conse- 

 quences from experimental facts, is an incessant exercise 

 of the student of physical science. But having thus fol- 

 lowed for a time the light of reason alone through a series 

 of phenomena, and emerged from them with a purely intel- 

 lectual conclusion, our duty is to bring that conclusion to 

 an experimental test. In this way we fortify our science, 



