292 Prof. Challis on Newton's "Foundation of all Philosophy" 



be an arrangement of matter possessing no realizable potential 

 energy, but uniformly hot — an undistinguisbable mixture of all 

 that is now definite and separate — chaos and darkness as in the 

 beginning." 



On the contrary, my researches, which proceed on the hypo- 

 thesis that all the forces of the universe are different modes of 

 the dynamical action of the vibrations and currents of the sether, 

 do indeed lead to the result that various forms of force are con- 

 vertible into that of heat, and the associated form of light ; but 

 at the same time they indicate how the repulsion of heat may, 

 by the modification which the dynamic action of undulations 

 undergoes when they are compounded together, be changed to 

 attraction. This transformation I have discussed particularly 

 in arts. 2 and 3 of my " Theory of Molecular Forces" contained 

 in the Philosophical Magazine for February 1860, and in the 

 Essay on the Sun's Heat already mentioned. I have there ad- 

 Verted to the important consequence of that theory, that the num- 

 berless vibrations which radiate from the individual atoms of a 

 body, producing by their dynamical action the body's internal 

 heat, by their subsequent composition form undulations to the 

 action of which the attraction of gravitation may be attributed. 

 Moreover, instead of concluding that "the sun must at present 

 be in the condition of a heated body cooling," I am led by my re- 

 searches to the inference that both the sun and the other bodies 

 of the solar system are, in regard to internal heat, in a state of 

 permanence, the fluctuations, if any, taking place about a mean 

 value which is constant so long as the dynamic action of the 

 universe is constant. Thus in two most important particulars, 

 one relating to the convertibility of heat into other forms of 

 force, and the other to the stability of the intrinsic heat of 

 masses, my results are directly opposed to those of Professor 

 Thomson. The analogy of nature, as inferred from the move- 

 ments of the planets, is certainly in favour of the stability of the 

 heat of the bodies of the solar system. I think, therefore, I 

 may justly conclude, having also indicated a possible source of 

 error in Professor Thomson's mode of philosophy, that there is 

 not the " sober scientific certainty " which he supposes in the 

 inferences he has drawn respecting the duration of the present 

 order of the universe. The powder that made can unmake ; but 

 as to when and how, physical science can reveal nothing. I have 

 felt the less scruple in discussing thus freely Professor Thom- 

 son's views, because, although they admit of question, he has 

 published them in a popular periodical, and because he has 

 since expressed (Phil. Mag. for June) his readiness to support 

 the correctness of the opinions contained in the article <c On 

 Energy ;; when he sees proper occasion for so doing. 



Cambridge, September 19, 1863. 



