8 S. P. Lcmgley — The History of a Doctrine. 



plied form, by generating an offspring specially inimical to true 

 ideas about radiant heat, and which is represented by a yet 

 familiar term. I mean " caloric." 



This word is still used loosely as a synonym for heat, but has 

 quite ceased to be the very definite and technical term it once 

 was. To me it has been new to find that this so familiar word 

 "caloric," so far as my limited search has gone, was apparently 

 coined only toward the last quarter of the last century. It is 

 not to be found in the earliest edition of Johnston's dictionary, 

 and, as far as I can learn, appears first in the corresponding 

 French form in the works of Fourcroy. It expressed an idea 

 which was the natural sequence of the phlogiston theory, and 

 which is another illustration that the evil which such theories 

 do lives after them. 



" Caloric " first seemingly appears, then, as a word coined by 

 the French chemists, and meant originally to signify the un- 

 known cause of the sensation heat, without any implication as 

 to its nature. But words, we know, though but wise men's 

 counters, are the money of fools ; and this one very soon came 

 to commit its users to an idea which was more likely to have 

 had its origin in the mind of a chemist at that time than of 

 any other, — the idea of the cause of heat as a material ingre- 

 dient of the hot body ; . something not, it is true, having weight, 

 but which it would have been only a slight extension of the 

 conception, to think might one day be isolated by a higher 

 chemical art, and exhibited in a tangible form. 



"We may desire to recognize the perverted truth which 

 usually underlies error and gives it currency, and be willing to 

 believe that even " caloric " may have had some justification 

 for its existence ; but this error certainly seems to have been 

 almost altogether pernicious for nearly the next eighty years, 

 and down even to our own- time. With this conception as a 

 guide to the philosophers of the last years of the eighteenth 

 century, it is not, at any rate, surprising if we find that at the 

 end of a hundred years from Newton the crowd seems to be 

 still going constantly farther and farther away from its true 

 goal. 



The doctrine of caloric is, however, always recognized as an 

 hypothesis more acceptable to chemists than to physicists, some 

 of whom still stand out for the theories of Newton's predeces- 

 sors, even through the darkest years ; so that the old idea of 

 heat, as a mode of motion, has by no means so utterly died 

 that it does not appear here and there during the last century, 

 and indeed, not only among philosophers, but even in a popu- 

 lar form. 



In an old English translation of Father Regnault's compila- 

 tion on physics, dated about 1730, I find, for instance, the 



