Chapman. — On the Peniiannirij of S(^}((r and Stellar Heat, 99 



times that amount. So that only in the time that the whole heat would be 

 radiated from the earth, Jupiter would only lose i-gi. 



It is manifest from these considerations that even if the collisions on 

 the earth are so infrequent that the heat generated is all radiated away, and 

 would be so if the collisions were hundreds of times more frequent ; still, 

 even assuming collisions still less frequent on Jupiter, a residue of heat 

 might be retained and continually accumulated. 



Taking, however, probabilities into account, we should be inclined to 

 infer that, considering the enormously greater bulk and mass of Jupiter, 

 collisions are vastly more frequent on Jupiter, as well as being three hun- 

 dred times more energetic than on the earth. We should, therefore, be led 

 to suppose that, assuming that in the case of such bodies as the earth, moon, 

 etc., all the heat generated is again dissipated, yet there is some magnitude 

 at which we should find the generation and dissipation of heat balance, 

 the planet being permanently maintained at the same temperature as the 

 surrounding space. 



All bodies larger than this, if started at zero, would have their tempera- 

 ture gradually rise to a point where, in consequence of increased radiation 

 from increased heat, the temperature would be maintained uniform so long 

 as the mass remained uniform ; but the mass would, in fact, not remain 

 uniform, but would continually grow by the addition of meteoric matter ; 

 the temperature would consequently also rise. Hence we see that all bodies 

 will constantly increase in magnitude, and all bodies over a certain critical 

 mass will constantly rise in temperature to a certain point beyond which the 

 only fluctuations will be due to the body increasing in mass and periodically 

 passing into relatively rich or poor meteoric fields, such as the August and 

 November meteor streams, etc. 



If we apply the foregoing considerations to those bodies which we know 

 best, we find that some of the bodies, as the satellites of the primary planets 

 — the Earth, Mars, the Asteroids, etc., appear all to be below the critical 

 pomt of mass, and we find them to be cold bodies. 



The larger bodies of the system— Jupiter, Saturn, Uranus, and 

 Neptune, certainly the two former, and probably the tw^o latter — are in 

 a state of intense heat, and are, therefore, above the critical point of 

 mass. 



The largest body of all in our system, viz., the Sun, is maintained at a 

 temperature egtimated by Secchi at not less than 10,000 degrees cent., and 

 perhaps many times that. 



It would be interesting to ascertain if the fixed stars, which are regarded 

 as the largest, are also the hottest, as they would be on the present 

 hypothesis, 



