﻿connected with Astronomical Physics. 575 



may well cooperate or even rival in fundamental import the 

 more catastrophic processes exemplified by the nebular theory 

 of Kant and Laplace, which [contrasted with the slow proce- 

 dure] involve an intense development of heat, with liquefaction 

 or vaporization of materials. 



If we leave provisionally out of view the primordial con- 

 stituents of matter, namely the " corpuscles M recognized to 

 belong to the domain of "Radioactivity": then, for the 

 building of systems, the only available substance appears to 

 be the substance of meteoritic bodies, which we can actually 

 handle and analyse in the laboratory. If it be conceded that, 

 by a natural process, systems cannot evolve out of nothing, 

 the visualizing of a purpose to be fulfilled by this everywhere 

 present meteoritic matter becomes of logical fitness ; and it 

 appears that no evolutionary theory of cosmical systems 

 becomes satisfactory, unless it recognizes this universal sub- 

 stance as a fundamental constituent (or basis), whether the 

 procedure concerned in any given case be regarded as slow, 

 spread over an extensive time-epoch, with unimportant 

 accumulation of heat ; or as catastrophic, as in the instance 

 of the nebular theory, where it appears that in the first stage 

 the nebula itself " may be regarded as a quasi gas, the mole- 

 cules of which are meteorites."" 



In our system, consider the numerous asteroids'*. It seems 

 to be often tacitly supposed or taken for granted that these 

 bodies in their movement of circulation about the sun were 

 once fluid or luminous, that they represent minor planets 

 which have cooled down. But they might never have been 

 incandescent or even have possessed a temperature worth 

 mentioning ; but may have been formed by the slow and 

 gradual accretion t of meteoritic bodies into that spherical 



* It appears a remarkable fact that the meteorites composing the ring 

 of Saturn circulate all substantially in one plane ; whereas this is not the 

 case with the asteroids, the orbits of which deviate considerably from a 

 plane. This would appear to indicate a mode of evolution not quite the 

 same in the two cases. Any suggestion, based on recognized, causes, 

 as to the mode of origin of the asteroidal ring, seems preferable to the 

 theory of an " exploded planet," the fragments of which are to represent 

 the asteroids. 



f There may be no objection to my quoting here a passage from a 

 letter received on April 9, 1893, from Sir George Darwin, as it bears on 

 the present subject : — 



" I cannot help feeling that Newcomb is wrong to throw over Bode's 

 law. It is wrong perhaps to call it a law, but for my part I believe that 

 the sequence of mean distances observed in the planets is due to physical 

 relationship amongst their perturbing powers on one another. I think 

 that sometime it will be discovered what that relationship is, and then 

 that it will appear that some term which remains negligible in the 

 interior planets has risen to importance when we get to Neptune so as to 

 disturb his times." 



