S. P. Langley — The History of a Doctrine. 7 



* 

 tionable. Let us consider, in illustration, any familiar instance 

 of oxidation, and try to look first for what was reasonable in 

 the eighteenth-century views of the cause of such phenomena. 



A piece of dry wood has in it the power of giving out heat 

 and light when set on iire ; but after it is consumed there is 

 left of it only inert ashes, which can give neither. Something, 

 then, has left the wood- in process of becoming ashes ; virtue 

 has gone out of it, or, as we should say, its potential energy 

 has gone. 



This- is, so far, an important observation, extending over a 

 wide range of phenomena, and, if it had presented itself to 

 the predecessors of Newton, it would probably have been 

 allied to the vibratory theories, and become proportionately 

 fruitful. But to his disciples, and to chemists and others, who, 

 without being perhaps disciples, were like all then, more or 

 less consciously influenced by the materiality of the corpuscu- 

 lar theory, it appeared that this virtue also was a material ema- 

 nation ; — that this energy was an actual ingredient of the 

 wood, — a crudeness of conception which seems most strange 

 to us, but is not perhaps unaccountable in view of the then 

 current thought. 



I have said that the progress of science is not so much that 

 of an army as of a crowd of searchers, and that a call in a 

 false direction may be responded to, not by one only, but by 

 the whole body. In illustration, observe that during the 

 greater part of the entire eighteenth century, this doctrine 

 was adopted by almost every chemist and by many physicists. 

 It had as general an acceptance among chemists then as the 

 kinetic theory of gases, for instance, has among physicists now, 

 and, so far as time is any test of truth, it was tested more 

 severely than the kinetic theory has yet been ; for it was not 

 only the lamp and guide of chemists, and to a great extent of 

 physicists also, but it remained the time-honored and highest 

 generalization of chemical science for over half a century, and 

 it was accepted not so much as a conditional hypothesis, as a 

 final guide, and a conquest for truth which should endure 

 always. And now where is it? Dissipated so utterly from 

 men's minds, that, to the unprofessional part of even an edu- 

 cated audience like this, " phlogiston," once a name to conjure 

 with, has become an unmeaning sound. 



There is no need to insist on the application of the obvious 

 moral to hypotheses of our own day. 



I have tried to recall for a moment all that " phlogiston " 

 meant a little more than a hundred years ago, partly because it 

 seems to me, that, though a chemical conception, physics is not 

 blameless for it, but chiefly because before it quitted the world 

 it appears to have returned to physics the wrong in a multi- 



