ORIGIN AND AGE OF THE SUNS HEAT. 265 



enormous store of heat possessed by the sun could 

 only have been derived from gravitation. For 

 example, a pound of coal falling into the sun from 

 an infinite distance would produce by its concussion 

 more than 6000 times the amount of heat that would 

 be generated by its combustion. It would, in fact, 

 amount to upwards of 65,000,000,000 foot-pounds — an 

 amount of energy sufficient to raise 1000 tons to a 

 height of 5 J miles. 



There are two forms in which the gravitation theory 

 has been presented : the first, the meteoric theory, 

 propounded by Dr. Meyer: and the second, the 

 contraction theory, advocated by Helm hoi tz. The 

 meteoric theory of the sun's heat has now been pretty 

 generally abandoned for the contraction theory 

 advanced by Helmholtz. Suppose, with Helmholtz, that 

 the sun originally existed as a nebulous mass, filling 

 the entire space presently occupied by the solar 

 system, and extending into space indefinitely beyond 

 the outermost planet. The total amount of work in 

 foot-pounds performed by gravitation in the conden- 

 sation of this mass to an orb of the sun's present size 

 can be found by means of the following formula given 

 by Helmholtz : — 



3 r 2 W 

 Work of condensation = ^ . -p— . g . 



M is the mass of the sun, m the mass of the earth, R 

 the sun's radius, and r the earth's radius. Taking — 

 M=4230 x 10 27 lbs., m = ll,920 x 10 21 lbs. 

 R= 2,328,500,000 feet, and r= 20,889,272 feet, 

 we have then, for the total amount of work performed 

 by gravitation in foot-pounds, 



3 ( 20,889,272'5) 2 x (4230 x 10 27 ) 2 

 5 " 2,328,500,000 x 11,920 x 10 21 

 = 168,790 x 10 36 foot-pounds. 



