S. P. Langley — The History of a Doctrine. 17 



rest of the animated creation % Some chemist whose earliest 

 recollections are of the strange and quite abnormal interest he 

 found as a child in making experimental mixtures of every 

 kind of accessible household fluid and solid ? Some astron- 

 omer who remembers that when a very little creature not only 

 the sight of the stars, but of any work on astronomy, even if 

 utterly beyond his childish comprehension, had an incompre- 

 hensible attraction for him ? I will not add to the list. There 

 are, at any rate, many here who will understand Melloni when 

 he tells how this radiant heat, commonplace to others, was 

 wonderful to his childish thought, and wrought a charm on it 

 such that he could not see wood burn in a fireplace, or look at 

 a hot stove, without its drawing his mind, not to the fire or 

 iron itself, but to the mysterious effluence which it sent. 



This was the youth of genius ; but let not any fancy that 

 genius in research is to be argued from such premonitions 

 alone, unless it can add to them that other qualification of 

 genius which has caused it to be named the faculty of taking 

 infinite pains. Melloni' s subsequent labors justified this last 

 definition also ; but I cannot speak of them here, further than 

 to say, that, after going over a large part of his work myself, 

 with modern methods and with better apparatus, he seems to 

 me the man, of all great students of our subject, who, in ref- 

 erence to what he accomplished, made the fewest mistakes. 



Melloni is very great as an experimenter, and owes much of 

 his success to the use of the newly invented thermopile, which 

 is partly his own. I can here, however, speak only of his 

 results, and of but two of these, — one generally known ; the 

 other, and the more important, singularly little known, at least 

 in connection with him. 



The first is the full recognition of the fact, partly antici- 

 pated by De la Roche, that radiant heat is of different kinds, 

 and that the invisible emanations differ among themselves just 

 as those of light do. Melloni not only established the fact, 

 but invented a felicitous term for it, which did a great deal to 

 stamp it on recognition, — the term " thermochrose," or heat- 

 color, which helps us to remember, that, as the visible and 

 app- iently simple emanation of light is found to have its 

 colors, so radiant heat, the invisible but apparently simple 

 emanation, has what would be colors to an eye that could see 

 them. This result is well known in connection with Melloni. 



The other and the greater, which is not generally known as 

 Melloni's, is the generalization that heat and light are effects of 

 one and the same thing, and merely different manifestations of 

 it. I translate this important statement as closely as possible 

 from his own words. They are that 



Am. Jour. Sci.— Third Series, Vol. XXXVII, No. 217.— Jan., 1889. 

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