•894 



SCIENCE. 



IN. S. Vol. IX. No. 235. 



able to authoritatively instruct us as to the 

 rapidity at which the ingathering would 

 take place? Can the problem be solved at 

 present with any such close approximation 

 to precison as to determine whether a liquid 

 or a gaseous state would or would not ensue ? 

 I assume that the most probable hypothesis 

 relative to the distribution and movements 

 of the meteorites is one that assumes that 

 they consisted of a swarm or belt revolving 

 about the sun in the general neighborhood 

 of the present orbit of the earth ; in other 

 words, some form of meteoroidal substitute 

 for the gaseous ring of the Laplacean hj'- 

 pothesis. The hypothesis may, doubtless, 

 diverge much in detail, and, indeed, in 

 some very important factors, but I assume 

 that no radical departure from this can be 

 entertained without endangering the pecu- 

 liar relations of the earth to the rest of the 

 solar system and the harmonious relations 

 of the whole ; without, in other words, 

 jeopardizing the consanguinity of the plan- 

 ets. If a distribution of meteorites bear- 

 ing any close resemblance to the Saturnian 

 rings, the foster parents of the nebular hy- 

 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 en- 

 larged so that they should lie outside 

 Roche'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 instantlj' outside 

 the limit and give place to a precipitate ten- 

 dency 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 presumption in 



such a case favorable to a slow rather than 

 to a rapid aggregation ? If a distribution 

 like the meteoroidal swarms that are asso- 

 ciated with the comets of the solar system 

 be assumed, a definite problem is set con- 

 cerning 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 problem involves the 

 balance between gravitative forces, revolu- 

 tionary forces and tidal forces, and the 

 gravitative forces are not simplj' those be- 

 tween the meteorites mutuallj^, but those 

 between the meteorites and the central so- 

 lar body and the exterior planetary bodies, 

 a complex of no mean intricacy. Is it cer- 

 tain that these forces would be so related 

 to each other as to produce a swift ingath- 

 ering of the whole swarm or belt, or, on 

 the other hand, an ingathering prolonged 

 through a considerable period ? If the lat- 

 ter be the case (and, in the absence of dem- 

 onstration, is it unreasonable to think it 

 quite as probable as the opposite) are there 

 any imperative grounds for assuming that 

 a liquid state of the earth would result? 

 Until the rate of aggregation is worked out 

 fully and rigorously are there any moral 

 prohibitions, strict or otherwise, to a free 

 interpretation of geologic and biologic evi- 

 dence on its own grounds? Is not the as- 

 sumption 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 any relief from the limitations 

 of time urged upon us. At first thought it 

 would, perhaps, seem that this alternative 

 would but intensify the limitations. Since 

 the argument for a short history is based 

 on the degree to which the earth is cooled, 

 an original cold state should but hasten the 



