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



on tlie whole theory of heat, since light being conceded to be 

 material, radiant heat, if affiliated to light, must be regarded 

 as material too, and Newton's influence is so permanent, that 

 we shall see this strange conclusion drawn by the contem- 

 poraries of Herschel from his experiments made a hundred 

 years later. 



It would seem then that the result of this unhappy corpus- 

 cular theory was more far-reaching than we commonly suppose, 

 and that it is hardly too much to say that the whole promising 

 movement of that age toward the true doctrine of radiant 

 energy is not only arrested by it, but turned the other way ; so 

 that in this respect the philosophy of fifty years later is actually 

 farther from the truth than that of Newton's predecessors, 

 and the immense repute of Newton as a leader, on the whole 

 so rightly earned, here leads astray others than his conscious 

 disciples, and, it seems to me, affects men's opinions on topics 

 which appear at first far removed from those he discussed. 

 The adoption of phlogiston was, as we may reasonably infer, 

 facilitated by it, and remotely Newton is perhaps also responsi- 

 ble in part for the doctrine of caloric a hundred years later. 

 After him, at any rate, there is a great backward movement. 

 We have a distinct retrogression from the ideas of Bacon and 

 Hobbes and Boyle. Night settles in again on our subject 

 almost as thick as in the days of the schoolmen, and there 

 seems to be hardly an important contribution to our knowledge, 

 in the first part of the eighteenth century, due to a physicist. 



"Physics, beware of metaphysics," said Newton, — words 

 which physicists are apt so exclusively to quote, that it seems 

 only due to candor to observe that the most important step, 

 perhaps, in the fifty years which followed the " Optics," came 

 from Berkeley, who, reasoning as a metaphysician, gave us 

 during Newton's lifetime a conception wonderfully in advance 

 of his age. Yet the " New Theory of Yision " was generally 

 viewed by contemporary philosophers as only an amusing 

 paradox, while " coxcombs vanquished] Berkeley with a grin ;" 

 and this contribution to science, — an exceptional if not a 

 unique instance of a great physical generalization reached by 

 a priori reasoning, — though published in 1709, remains in 

 advance of the popular knowledge even in these closing years 

 of the nineteenth century. 



In the meantime a new error had risen among men, — a new 

 truth, as it seemed to them, — and a thing destined to have a 

 strong reflex action on the doctrine of radiant energy. It 

 began with the generalization of a large class of phenomena 

 which we now "associate with the action of oxygen, then of 

 course unknown, a generalization useful in itself, and accom- 

 panied by an explanation which was not in its origin objec- 



