THE PROBABLE AGE OF THE WORLD. 671 



from an infinite distance would produce 6,000 times more heat from 

 concussion than it would generate by its combustion. An idea of the 

 amount of energy exerted by one pound weight falling into the sun 

 will be conveyed by stating that it would be sufficient to hurl the 

 Warrior, with all its stores, guns, and ammunition, over the top 

 of Ben Nevis ! 1 But, if we accept gravitation as the source of energy, 

 we accept a cause, the value of which can be mathematically deter- 

 mined with very considerable accuracy. 



The amount of heat given off by radiation in a year s is known ; 

 the total amount of work performed by gravitation in condensing a 

 nebulous mass to an orb of the sun's present size is known. The re- 

 sult is, that the amount of heat thus produced by gravitation would 

 suffice for about twenty millions and a quarter of years. This is on 

 the assumption that the nebulous matter composing the sun was origi- 

 nally cold, and that heat was generated in it by the process of con- 

 densation only. It is, however, quite conceivable that the nebulous 

 mass possessed a store of heat previous to condensation, and that the 

 very reason why it existed in the gaseous condition was that its tem- 

 perature was excessive. The particles composing it would have had 

 a tendency, in virtue of gravitation, to approach one another if they 

 had not been kept apart by the repulsive energy of heat; it is not, 

 then, unreasonable to suppose that the attenuated and rarefied mass 

 was vaporous by reason of heat, and began to condense only when its 

 particles began to cool. By the known laws under which heated 

 gases condense, the amount of heat originally possessed by the gas 

 bears a definite and known proportion to the amount of heat gener- 

 ated by condensation ; and, on the assumption that the analogy holds 

 good in the case of the sun, which holds in the condensation of other 

 heated gases, nearly fifty millions of years' heat must have been stored 

 up in the mass as original temperature. This, added to the twenty 

 and a quarter millions which resulted from gravitation, gives rather 

 more than seventy millions of years' sun-heat. 



As, however, this quantity gives the total amount of heat given 

 out by the mass since it began to condense, the earth could not have 

 had an independent existence till long after that time. The sun must 

 have had time to condense from its outer limits as a nebula, to within 



1 The velocity with which a body falling from an infinite distance would reach the 

 sun would be equal to that which would be generated by a constant force equal to the 

 weight of the body at the sun's surface operating through a space equal to the sun's 

 radius. One pound would at the sun's surface weigh about twenty-eight pounds. Taking 

 the sun's radius at 441,000 miles, the energy of a pound of matter falling into the sun 

 from infinite space would equal that of a 28-pound weight descending upon the earth from 

 an elevation of 441,000 miles, supposing the force of gravity to be as great at that ele- 

 vation as it is at the earth's surface. It would amount to upward of 65,000,000,000 

 foot-pounds. 



2 The total amount radiated from the whole surface of the sun per annum is 8,340 

 x 10 30 foot-pounds. Croll, 346. 



