144 ANNUAL OF SCIENTIFIC DISCOVERY. 



Some interesting speculations suggested by the new theory of heat 

 have been recently brought out by Prof. W. Thomson. The heat of 

 a heavenly body placed under the same conditions as the sun, must, 

 it has been said, be ultimately exhausted by its rapid emission. This 

 assertion assumes the matter composing the sun to have certain prop- 

 erties like those of terrestrial matter with respect to the generation 

 and emission of heat ; but Prof. Thomson's argument places the sub- 

 ject on better grounds, admitting, always, the truth. of the new theory 

 of heat. That theory asserts, in the sense which I have already 

 stated, the exact equivalence of heat and motive power ; and that a 

 body, in sending forth heat, must lose a portion of that internal motion 

 of its constituent particles on which its thermal state depends. Now 

 we know that no mutual action of these constituent particles can con- 

 tinue to generate motion which might compensate for the loss of 

 motion thus sustained. This is a simple deduction from dynamical 

 laws and principles, independent of any property of terrestrial matter 

 which may possibly distinguish it from that of the sun. Hence, then, 

 it is on these dynamical principles that we may rest the assertion that 

 the sun cannot continue for an indefinite time to emit the same quan- 

 tity of heat as at present, unless his thermal energy be renovated from 

 some extraneous source. The same conclusion may be applied to all 

 other bodies in the universe which, like our sun, may be centers of 

 intense heat ; and, hence, recognizing no adequate external supplies 

 of heat to renovate these existing centers of heat, Prof. Thomson 

 concludes that the dispersion of heat, and consequently of physical 

 energy, from the sun and stars into surrounding space without any 

 recognizable means of reconcentration, is the existing order of nature. 

 In such case the heat of the sun must ultimately be diminished, and 

 the physical condition of the earth therefore altered, in a degree 

 altogether inconsistent with the theory of non-progression. 



Mr. Rankine, however, has ingeniously suggested an hypothesis 

 according to which the reconcentration of heat is conceivable. As- 

 suming the physical universe to be of finite extent and surrounded by 

 an absolute vacuum, radiant heat (supposing it to be propagated in 

 the same way as light) would be incapable of passing into the vacuum, 

 and would be reflected back to foci corresponding to the points from 

 which it emanated. A reconcentration of heat would thus be effected ; 

 and any of the heavenly bodies which had previously lost their heat, 

 might, on passing through these foci, be rekindled into bright centres 

 of radiant heat. I have alluded more particularly to this very ingen- 

 ious, though, perhaps, fanciful hypothesis, because some persons have, 

 I believe, regarded this view of the subject as affording a sanction to 

 the theory of non-progression; but even if we should admit its truth 

 to the fullest extent, it may be deemed, I think, entirely inconsistent 

 with that uniformity and permanence of physical condition in any of 

 the heavenly bodies which the theory just mentioned requires in our 

 own planet. The author of this hypothesis did not possibly contem- 

 plate any such application of it ; nor am I aware how far he would 

 advocate it as really applicable to the actual constitution of the 



