Mr. M. M. P. Muir on Chemical dotation. 13 



known, in the same space " (I quote from Prof. Jevons's work 

 on the Principles of Science). Provided that a theory does 

 not go against the primary laws of thought and of Xature, we 

 must accept it, however absurd it may appear, if it be in ac- 

 cordance with facts. But in applying the deductive method 

 of scientific reasoning, we are apt to forget that a theory, how- 

 ever perfect and satisfactory it may appear, is to be put to the 

 severest test ; it is only by showing that the known facts are 

 explained by the theory, by foretelling facts which must be 

 facts if the theory be true, and again by showing that these 

 are indeed true, that a scientific theory can pass successfully 

 into the number of accepted hypotheses. iSTewton's method of 

 treating the theory of gravitation, and Faraday's method 

 throughout his magnificent series of ' Experimental Re- 

 searches,' are typical examples of the true positions of Theory 

 and Fact in scientific investigation. If it can be shown, there- 

 fore, that the molecular theory is not in accordance with 

 facts, or is self-contradictory, it must be discarded ; but to re- 

 fuse to accept it because it has not been gained by purely 

 inductive reasonings is simply, it appears to me, to show an 

 ignorance of the true method of scientific investigation. 



26. In examining the position of the molecular theory of 

 matter as a scientific hypothesis, I would inquire : — Is it in 

 accord with known facts ? does it enable us to explain what 

 would else appear to be disconnected phenomena ? and are we 

 able by its aid to predict phenomena which are afterwards 

 proved to be true ? In the following statement concerning 

 the physical proofs of the molecular theory, I have drawn 

 largely from Prof. Clerk Maxwell's ' Treatise on Heat.' 



27. The molecular theory is in accord with known facts 

 concerning the condition of hot bodies. 



A hot body possesses a certain amount of energy. This 

 energy is capable of being changed from potential into kinetic 

 energy; but such a change involves motion of some kind. 

 "When a hot body loses heat by radiation, this radiation must 

 be effected either by the motion of material particles from the 

 hot body to the body which receives the heat, or by the motion 

 of some medium which fills the space between the body giving 

 out and the body receiving heat ; hence the particles on the 

 outer surface of a body radiating heat must be in a state 

 of motion. But hot bodies are continually radiating heat ; 

 therefore their outer particles must be in a state of continual 

 motion ; hence part, at least, of the energy of a hot body 

 exists in the form of kinetic energy. But the motion of the 

 particles of a hot body cannot be the motion of the body 

 as a whole ; otherwise the motion would be visible to us ; it 



