342 THE POPULAR SCIENCE MONTHLY. 



much farther than they now are from their primaries, when they were 

 able to take on the globular form from the nebulous rings or collection 

 of nodules out of which they were made. 



Taking the above estimates, and applying the law to the case of 

 Mars's nearest satellite, we find that its orbit must have been at least 

 17f its present diameter when it was able to take on its globular form 

 from its nebulous ring. 



This establishes beyond doubt the fact to be proved, and gives us 

 some idea of the vast dimensions of the solar system when this last 

 nebulous satellite of Mars was formed. 



What, then, must have been the distance of the first nebulous planet 

 from the centre of the system, when it was formed ? This, of course, can 

 be only vaguely guessed, as we have no reliable criterion to judge by. 



The Resisting Medium. The introduction of the hypothesis of a 

 resisting medium to account for this contraction of planetary orbits 

 seems at first sight to involve a condition fatal to the continued activity 

 of the material universe; for, if there be a resisting medium, which is 

 gradually bringing our system to a state of rest by its reaction on the 

 bodies moving in it, it is but reasonable to suppose that it should pro- 

 duce like results on all other systems, and thus ultimately bring the 

 entire universe of matter into the quiet sleep of death. But that this 

 is not the normal tendency, however, when applied to the universe as a 

 ichole, we have the most abiding assurance, without any investigation 

 of this kind ; for, if such be the tendency now, it always would have been 

 the tendency, in which case the end would have been accomplished 

 during the eternities of the past, and we would not be here to-day to 

 dread its approach. 



Still the following question, or its equivalent, will press itself on 

 many minds : How can the perfect conservation of force, which is so 

 essentially necessary for the continued activity of the material universe, 

 be reasonably accounted for, if there be a resisting medium in all 

 space through which it must ever move ? This pressing yet interest- 

 ing question leads directly to the second division of our subject, which 

 will now be discussed. 



In order to give this question a suitable reply, as well as to show 

 how the perpetual activity of the material universe may be maintained, 

 while moving in this resisting medium, we will trace the history of some 

 given solar system from its original nebulous state, down through its 

 life-sustaining period, thence to its final destiny; and then discover, if 

 possible, a means by which it may be reinvigorated or resurrected to a 

 new planetary life. For this purpose it seems necessary to present 

 very briefly, however, for want of space one illustration, reaching 

 through the various stages in the grand round of successive changes 

 through which all planetary systems seem to be passing. Our solar 

 system will be taken as the illustrative example. 



In tracing the history of the system from its nebulous state down 



