THE AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 2'29 



gaseous ring of the Laplacean hypothesis. The hypothesis may. dout)t- 

 less, diverge much in detail, and, indeed, in some very impoit:int 

 factors, but I assume that no radical departure from this can be enter- 

 tained without endangering the peculiar relations of the earth to the 

 rest of the solar system and the harmonious relations of the whole; 

 without, in other words, jeopardizing the consanguinit}^ of the planets, 

 if a distribution of meteorites bearing any close resemblance to the 

 Saturnian rings, the foster parents of the nebular hj^pothesis, be 

 assumed, a definite problem is presented for determination. If the 

 rings of Saturn, which are quite certainly formed of discrete solid 

 matter, were to be enlarged so that they should lie outside Eoche's 

 limit, and so escape the sphere of specially intense tidal strain which 

 will permit no aggregation, what reason is there to think that they 

 would gather together precipitately? Does the tidal influence, which, 

 within Roche's limit, is able to tear a satellite to pieces, cease instantly 

 outside the limit and give place to a precipitate tendency to come 

 clashing together? On the contrary, is it not difficult to demonstrate, 

 by rigorous processes, even the method by which the meteorites will 

 aggregate, much less their rate, or even to demonstrate that, apart from 

 extraneous causes, they will fall together at all ? Is not the presump- 

 tion in such a case favorable to a slow rather than to a rapid aggrega- 

 tion ? If a distribution like the meteoroidal swarms that are associated 

 with the comets of the solar system be assumed, a definite problem is 

 set concerning which some appeal to observation is possible. Here 

 the observed tendency is toward dispersion rather than aggregation. 

 In either of these assumptions, or in any other assumption, the prob- 

 lem involves the balance between gravitative forces, revolutionary 

 forces, and tidal forces, and the gravitative forces are not simply those 

 between the meteorites mutually, but those between the meteorites and 

 the central solar body and the exterior planetar}- bodies, a complex of 

 no mean intricacy. Is it certain that these forces would be so related 

 to each other as to produce a swift ingathering of the whole swarm or 

 belt, or, on the other hand, an ingathering prolonged through a con- 

 siderable period? If the latter be the case (and, in the absence of dem- 

 onstration, is it unreasonable to think it quite as probable as the oppo- 

 site?), are there any imperative grounds for assuming that a liquid state 

 of the earth would result i Until the rate of aggregation is worked out 

 fully and rigorously, are there any moral prohibitions, strict or other- 

 wise, to a free interpretation of geologic and biologic evidence on its 

 own grounds ? Is not the assumption of a white-hot liquid earth still 

 quite as much on trial as any chronological inferences of the biologist 

 or geologist? 



It of course remains to be seen whether the alternative hypothesis 

 of an earth grown up slowly in a cold state, or in some state less hot 

 than that assumed in the address, would afford anv relief from the 



