356 



THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



resulted from the destruction of a still older 

 land, and so on in like manner back into the un- 

 known past. 



It has now been proved, by the foregoing 

 very simple and obvious method, that the age of 

 the earth must be far more than 20,000,000 or 

 80,000,000 years. This method, it is true, does 

 not enable us to determine with anything like 

 accuracy the actual age of the globe, but it 

 enables us to determine with absolute certainty 

 that it must be far greater than 20,000,000 years. 

 We have not sufficient data to determine how 

 many years have elapsed since life began on the 

 globe, for we do not know the total amount of 

 rock removed by denudation ; but we have data 

 perfectly sufficient to show that it began far more 

 than twice 20,000,000 years ago. 



But if the present order of things has been ex- 

 isting for more than 20,000,000 years, then the sun 

 must have been illuminating our globe for that 

 period, and, if so, then there must have been some 

 other source than that of gravitation from which 

 the sun derived its energy, for gravitation, as we 

 have seen, could only have supplied the present 

 rate of radiation for about one-half that period. 



It is perfectly true, as has been stated, that 

 the length of time that the sun could, by its ra- 

 diation, have kept the earth in a state fit for ani- 

 mal and vegetable life, must have been limited 

 by the store of energy in the form of heat which 

 it possessed. But it does not follow as a neces- 

 sary consequence, as is generally supposed, that 

 this store of energy must have been limited to the 

 amount obtained from gravity in the condensa- 

 tion of the sun's mass. The utmost that any 

 physicist is warranted in affirming is simply that 

 it is impossible for him to conceive of any other 

 source. His inability, however, to conceive of 

 another source cannot be accepted as a proof 

 that there is no other source. But the physical 

 argument that the age of our earth must be lim- 

 ited by the amount of heat which could have 

 been received from gravity is in reality based 

 upon this assumption — that, because no other 

 source can be conceived of, there is no other 

 source. 



It is perfectly obvious, then, that this mere 

 negative evidence against the possibility of the 

 age of our habitable globe being more than 

 20,000,000 or 30,000,000 years is of no weight 

 whatever when pitted against the positive evi- 

 dence here advanced that its age must be far 

 greater. 



Now, in proving that the antiquity of our 

 habitable globe must be far greater than 20,000,- 



000 or 30,000,000 years, we prove that there 

 must have been some other source in addition to 

 gravity from which the sun derived his store of 

 energy ; and (his is (he point which I have been 

 endeavoring (o reach hy (his somewhat lengthy dis- 

 cussion. 



Are we really under any necessity of assum- 

 ing that the sun's heat was wholly, or even main- 

 ly, derived from the condensation of his mass by 

 gravity ? According to Ilelmholtz's theory of the 

 origin of the sun's heat by condensation, it is as- 

 sumed that the matter composing the sun, when 

 it existed in space as a nebulous mass, was not 

 originally possessed of temperature, but that the 

 temperature was given to it as the mass became 

 condensed under the force of gravitation. It is 

 supposed that the heat given out was simply the 

 heat of condensation. But it is quite conceivable 

 that the nebulous mass might have been pos- 

 sessed cf an original store of heat previous to 

 condensation. 



It is quite possible that the very reason why 

 it existed in such a rarefied or gaseous condition 

 was its excessive temperature, and that conden- 

 sation only began to take place when the mass 

 began to cool down. It seems far more probable 

 that this should have been the case than that 

 the mass existed in so rarefied a condition with- 

 out temperature. For why should the particles 

 have existed in this separate form when devoid 

 of the repulsive energy of heat, seeing that, in 

 virtue of gravitation, they had such a tendency to 

 approach one another ? 



It will not do to begin with the assumption 

 of a cold nebulous mass, for, the moment that 

 the mass existed as such, condensation — under 

 the influence of the mutual attraction of its par- 

 ticles — would commence. We must therefore as- 

 sume either that the mass was created at the mo- 

 ment condensation began, or that, prior to this 

 moment, it existed under some other form. There 

 are few, I think, who would be willing to adopt 

 the former alternative. If we adopt the latter 

 we must then ask the question, " In what condi- 

 tion did this mass exist prior to the commence- 

 ment of condensation?" The answer to this 

 question would naturally be that it existed in a 

 condition of excessive temperature, the repulsive 

 force of heat preventing the particles approach- 

 ing one another. In short, the excessive tem- 

 perature was the very cause of the nebulous con- 

 dition. 



But if the mass was originally in a heated 



condition, then in condensing it would have to 



. part not only with the heat of condensation, but 



