Date of the Glacial and the Upper Miocene Period. 373 



wards the sun with an original velocity before coming under the 

 sensible influence of the sun's attraction. In this case a greater 

 amount of heat would be generated by the meteor than would 

 have resulted from its merely falling into the sun under the in- 

 fluence of gravitation. But then meteors of this sort must be 

 of rare occurrence. And we have but very little warrant on this 

 ground to conclude that the amount of energy communicated 

 to the sun since the geological history of our globe began could 

 have been much more than the equivalent of the work performed 

 by gravitation in the condensation of his mass. 



It is highly probable, as Professor Sir William Thomson has 

 concluded, that the sun in the early geological periods must have 

 been far hotter than at present, owing to his excessively high 

 temperature. When the sun's mass was in an intensely heated 

 condition, filling perhaps the entire sphere occupied by the pla- 

 netary system, it would no doubt be in a gaseous state, and of 

 excessively small density. Gases are known to be bad radiators ; 

 and it is probable that a gaseous mass of such rarity would ra- 

 diate its heat into space with some difficulty ; and this might 

 tend in a great measure to lessen the excessive rate of radiation 

 which would otherwise result from so prodigious a temperature. 



The question naturally suggests itself, how could the sun's 

 mass have been originally raised to such a high temperature as 

 we have assumed ? What power could raise the temperature of 

 the sun's mass to such an extent as to cause it to become an in- 

 candescent gas of such rarity ? By what means could this mass 

 become possessed of 50,000,000 years' heat, as we have con- 

 cluded, even before it began to condense ? There is nothing at 

 all absurd or improbable in the supposition that such an amount 

 of energy might have been communicated to the mass. The 

 Dynamical Theory of Heat affords an easy explanation of at 

 least how such an amount of energy may have been communi- 

 cated. Two bodies, each one-half the mass of the sun, moving 

 directly towards each other with a velocity of 476 miles per se- 

 cond, would by their concussion generate in a single moment the 

 50,000,000 years' heat. For two bodies of that mass moving 

 with a velocity of 476 miles per second would possess 4149 x 10 38 

 foot-pounds of energy in the form oivis viva ; and this, converted 

 into heat by the stoppage of their motion, would give an amount 

 of heat which would cover the present rate of the sun's radiation 

 for a period of 50,000,000 years. 



Why may not the sun have been composed of two such 

 bodies ? And why may not the original store of heat possessed 

 by him have all been derived from the concussion of these two 

 bodies ? Two such bodies coming into collision with that velo- 

 city would be dissipated into vapour by such an inconceivable 



Phil Mag. S. 4. Vol. 35. No. 238. May 1868. 2 C 



