420 Observations on Mr. Herapath's Theory. [Dec, 



a distance, without contact, and without materially affecting the 

 temperature of the intermediate air. Motion cannot be so com- 

 municated ; heat, therefore, cannot be motion. Here indeed it 

 is possible Mr. 11. will call in aid the ethereal fluid which he 'has. 

 gratuitously supposed to fill all space. The only proper answer 

 to such a supposition is, ' Show this fluid to me ; prove its 

 existence by some other evidence than its being necessary to 

 support your theory ; for that argument can have little weight 

 which founds the truth of a theory upon a supposed fluid, the 

 existence of which fluid itself rests only upon the truth of the 

 theory.' But still, grant the fluid to exist ; for when once the 

 basis of experiment is departed from, and imagination is let 

 loose, there is no reason why its liberty should be circumscribed. 

 This ethereal fluid, must, however, for the purpose, be supposed 

 capable of receiving and communicating temperature, and this 

 power cannot, by any mode of reasoning, be confined to its 

 relation to bodies distant from each other. But a power of 

 receiving and communicating temperature must most evidently 

 be perceptible to experiment ; and we have, therefore, a fluid 

 with evidently perceptible qualities, which is utterly incapable, 

 either by its qualities, or in any other way, of being perceived. 



But again, Mr. H. assumes as one of the bases of his theory 

 (of course without any proof), " that what we call heat, arises 

 from an intestine motion of the atoms, or particles, and is propor- 

 tional to their individual momentum." * These particles he has 

 assumed to be * of different sizes and figures" in different 

 bodies, and the temperature of these bodies he has considered 

 to be equal, when the velocities of their particles are inversely 

 proportional to their magnitude ; that is, when the momenta of 

 the particles are equal. The velocities, therefore, of the particles 

 of different bodies will be different at the same temperature. 



Now if a body, A, be placed in contact with another body, B, 

 having atoms of a greater magnitude, but a velocity less in an 

 inverse proportion, that is, according to Mr. H. being of the 

 same temperature, "the atoms will be continually impinging on 

 one another, and on the side of the adjoining body." Now it is 

 evident that the atoms of A may impinge upon the atoms of B, 

 whether they be approaching A or receding from it; that is, the 

 atoms of A having a greater velocity, may either meet or over- 

 take the atoms of B ; and the probabilities will be nearly equal 

 as to the one or the other. But whether the atoms be elastic or 

 hard, having the properties of elastic bodies which Mr. H. has 

 attributed to them, or be hard with the properties usually 

 ascribed to hard bodies, still if one atom a, of the body A, having 

 a oreater velocity than the atom b, of the body B, overtake the 

 slower atom, the atom a will lose some of its velocity, which will 

 be communicated to the atom b, and thence among the other 



* Avnah of Philosophy for April. 



