ON THE PROBABLE ORIGIN AND AGE OF THE SUN. 



351 



of heat that would be generated by its combus- 

 tion. It would, in fact, amount to upward of 

 65,000,000,000 foot-pounds — an amount of en- 

 ergy sufficient to raise 1,000 tons to a height of 

 five and a half miles. 



There are two forms in which the gravitation 

 theory has been presented : 1. The meteoric 

 theory, propounded by Dr. Meyer ; and, 2. The 

 contraction theory, advocated by Helmholtz. 

 The meteoric theory of the sun's heat has now 

 been pretty generally abandoned for the contrac- 

 tion theory advanced by Helmholtz. Suppose, 

 with Helmholtz, that the sun originally existed 

 as a nebulous mass, filling the entire space pres- 

 ently occupied by the solar system, and extend- 

 ing into space indefinitely beyond the outermost 

 planet. The total amount of work in foot- 

 pounds performed by gravitation in the condensa- 

 tion of this mass to an orb of the sun's present 

 size can be found by means of the following 

 formula given by Helmholtz : 



Work of condensation =: _ . I a. 



5 Rm 



M is the mass of the sud, m the mass of the 

 earth, R the sun's radius, and r the earth's radi- 

 us. Taking — 



M = 4,230 x 10" lbs., m = 11,920 x 10 51 lbs., 

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

 we have, then, for the total amount of work per- 

 formed by gravitation in foot-pounds : 



3 (20 ,889,272.5)2 x (4,230 x 10 "^ 

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

 = 168,790 x 10 36 foot-pounds. 



The amount of heat thus produced by gravita- 

 tion would suffice for 20,237,500 years. 



The conclusions are based upon the assump- 

 tion that the density of the sun is uniform 

 throughout. But it is highly probable that the 

 sun's density increases toward the centre, in 

 which case the amount of work performed by 

 gravitation would be something more than the 

 above. 



At this point, in reference to the age of our 

 globe, Geology and Physics are generally sup- 

 posed to come into direct antagonism. For, if it 

 be true, as physicists maintain, that gravitation 

 is the only possible source from which the sun 

 could have derived its store of energy, then the 

 sun could not have maintained our globe at its 

 present temperature for more than about 20,000,- 

 000 years. " On the very highest computation 

 which can be permitted," says Prof. Tait, "it 

 cannot have supplied the earth, even at the pres- 

 ent rate, for more then about 15,000,000 or 20,- 



000,000 years." > The limit to the age of the 

 sun's heat must have limited the age of the hab- 

 itable globe. All the geological history of the 

 globe would necessarily be comprehended within 

 this period. If the sun derived its heat from the 

 condensation of its mass, then it could not pos- 

 sibly be more than about 20,000,000 years since 

 the beginning of the Laurentian period. But 

 20,000,000 years would be considered by most 

 geologists to represent only a comparatively 

 small portion of the time which must have 

 elapsed since organic life began on our globe. 



It is true that the views which formerly pre- 

 vailed among geologists, in regard to the almost 

 unlimited extent of geological time, have of late 

 undergone very considerable modifications ; but 

 there are few geologists, I presume, who would 

 be willing to admit that the above period is suffi- 

 cient -to comprehend the entire history of strati- 

 fied rocks. 



It is the facts of denudation which most for- 

 cibly impress the mind with a sense of immense 

 duration, and show most convincingly the great 

 antiquity of the earth. 



We know unquestionably that many of the 

 greatest changes undergone by the earth's crust 

 were produced, not by convulsions and cata- 

 clysms of Nature, but by those ordinary agencies 

 that we see at work every day around us, such as 

 rain, snow, frost, ice, chemical action, etc. Val- 

 leys have not been produced by violent disloca- 

 tions, nor the hills by upheavals, but both have 

 been carved out of the solid rock by the silent 

 and gentle agency of chemical action, frost, rain, 

 ice, and running water. In short, the rocky face 

 of our globe has been moulded into hill and dale, 

 and ultimately worn down to the sea-level by 

 means of these apparently trifling agents, not 

 merely once or twice, but probably dozens of 

 times over during past ages. Now, when we re- 

 flect that with such extreme slowness do these 

 agents perform their work that we might, if we 

 could, watch their operations from year to year 

 and from century to century without being able 

 to perceive that they make any sensible impres- 

 sion, we are necessitated to conclude that geo- 

 logical periods must be enormous. The utter 

 inadequacy of a period of 20,000,000 years for 

 the age of our earth is demonstrable from the 

 enormous thickness of rock which is known to 

 have been removed off certain areas by denuda- 

 tion. I shall now briefly refer to a few of the 

 many facts which might be adduced on this 

 point. 



J " Recent Advances in Physical Science," p. 1T5. 



