

the Foundations of Dynamics. 5 



sion from experiment, more perhaps than preconceived views 

 about caloric, that retarded progress in radiant heat for so 

 many years. We are reminded of Darwin's saying that a bad 

 observation is more mischievous than unsound theory. It 

 would be interesting to inquire upon what grounds we now 

 reject the plain answer which Herschel thought himself to 

 have received from experiment. I do not recall a modern 

 investigation in which the heat and light absorptions are 

 proved to be equal for the various parts of the visible spec- 

 trum. Can it be that after all we have nothing but theory 

 to oppose to Herschel's facts V 



Yes, that is all, and, as Lord Eayleigh well knows, it is 

 amply enough. Whoever examines the facts again will do 

 so not to substantiate our present theory but in the hope of up- 

 setting it. Success is of course just conceivable, but, when it 

 comes, there will be time enough to reopen the question. Lord 

 Rayleiglr's words may be distorted, and may even suggest false 

 meanings to minds with a crooked turn in them ; so may many 

 of the apparent admissions about unprovableness in this 

 paper of mine, but, whether it gives occasion to the enemy to 

 blaspheme or not, it is true that a host of doctrines are 

 believed because they form part of a consistent scheme rather 

 than because of any seriously attempted, still less any really 

 achieved, experimental proof. And to pull one of these neatly 

 fitting blocks from its niche will demand the strength of more 

 than one, of more than several, so-called crucial experiments. 

 There comes a time indeed when the weight of experimental 

 evidence suffices to uproot a portion of tightly fitting theory ; 

 but seldom, as I think, without some looseness or uneasiness 

 being first detected, and never without a betrayal of rottenness 

 at the root. 



Why do Physicists deny that matter can be moved by 

 mental power from a distance without physical mechanism ? 

 Why does modern science reject the whole of a certain class 

 of miracles, in the teeth of an immense record of direct 

 experimental evidence ? Solely because these things do not 

 fit in with such coherent views of the universe as they have 

 at present been able to frame. 



Why, again, do we accept a multitude of unverified state- 

 ments, such as, that every portion of radiation, whether it be 

 of light or of sound, is intrinsically energy, and must, if 

 absorbed, result in heat ; that every muscular contraction of 

 an animal corresponds to the combustion of a portion of his 

 food ; that a given gas consists of particles of approximately 

 specified size and weight travelling at a certain average 

 speed; that a medium connects every pair of bodies which are 



