Rev. Maxwell S. Close — Extent of Geological Time. 451 



Vegetable and animal life for a time as long as the geologist "would 

 require. If I might presume to express an opinion on the subject, 

 it seems to me that this is the argument which is calculated to cause 

 the greatest anxiety to geologists. The period of the sun's radiation 

 depends upon two principal assumptions, not to mention some others 

 of much less importance, and these are the amount of heat at the 

 disposal of the sun, and his power of radiating it. As to the latter, 

 his radiating power, the physicists have kindly come to our help and 

 mitigated our difficulty considerably by showing us how to restrain 

 his otherwise too lavish radiation when he was still young. We 

 shall content ourselves with thanking them for their help, and pass 

 to the other point. Now, then, as to the amount of potential heat 

 that there was in the solar system nebula to be afterwards realized 

 by the sun. This is calculated on two assumptions, both, it must be 

 candidly confessed, very reasonable ones, jet both we must at the 

 same time claim to be not proven. The first is, that the nebula 

 whence the solar system was to be formed had no energy worth 

 speaking of proportionately, but the potential energy of gravitation 

 wherewith to start on its career of evolution ; and the second is that 

 the unit of gravitation, at least within the range of the original 

 nebula, and of the resulting solar system, has always been constant. 

 Dr. Croll's suggestion ia answer to the first of these is well known 

 — viz. that it may have been the very heat of the nebula which 

 caused it to exist as such, and that its heat may have been produced 

 by the collision of two cosmical masses. We shall not go into this 

 now ; we shall merely endeavour to remove the objection that has 

 been made to it. It is admitted that such collisions occasionally 

 take place, but it is objected that they are rare, and that the chance 

 of any particular cosmical body colliding with another within a con- 

 siderable number of millenniums is indefinitely small. Most true : 

 but in the first place for how many cosmical asons were we waiting 

 for our collision ? On foot of this account the geologists have practi- 

 cally unlimited funds to their credit in the Bank of Time. But 

 besides this there seems to be some misconception in this objection 

 of the improbability of this collision. The very same accident or co- 

 incidence may be to one observer a matter of indifference, and per- 

 fectly credible on comparatively slender testimony, and it may be to 

 another so remarkable and striking as to be not easily believed, or 

 only to be explained as a direct interposition of Providence — accord- 

 ing to the point of view of the observer, according as he happens to 

 be concerned with the coincidence. It seems to me that the present 

 objection has no weight; it has scarcely any meaning except from 

 the anthropocentric point of view, and that cosmologists ought to 

 consider cosmological questions from a higher standpoint. But, 

 besides this, not only does Dr. Croll's suggestion afford relief to the 

 geologists, but I respectfully submit that the physicists themselves 

 might be glad to avail themselves of it. 



We are told most truly that the falling together of the materials 

 of a cold nebula is " a thoroughly intelligible source of heat." But 

 what about the source of the cold nebula itself? Is that a thoroughly 



