PLANETARY RINGS AND NEW STARS. 473 



la carefully tracing the conspicuous scenes which must mark the 

 end of a planetary career, and thus obtaining a more correct interpre- 

 tation of the rare and mysterious characters occasionally inscribed in 

 our skies, very interesting information may be obtained of the diversi- 

 fied contents of space, and the long term of existence assigned to each 

 of the numerous worlds of creation. If the dominions of other suns be 

 equally rich as our solar region in mundane objects, it may not be ex- 

 travagant to suppose that, in our universe, the large primary and sec- 

 ondary planets enlivened by the genial influence of more than twenty 

 millions of stellar bodies might equal in number half the population of 

 our globe. Now. the average mortality in the human family is about 

 one death every second, while astronomical records show that only 

 twenty-three temporary stars appeared within the past two thousand 

 years. Taking their appearance as records of planetary fate, it would 

 follow that a century is as small a part of the career of a planet as two 

 seconds is of human life ; and that the few thousand years in which 

 the history of our race is comprised is scarcely two minutes in the im- 

 measurable age of our world. 



Yet these considerations will perhaps give an inadequate idea of the 

 long endurance of the great works in creation's wide domain. Accord- 

 ing to the opinions of Laplace, besides the systems over which visible 

 stars preside, there are others, equally numerous in which the central 

 bodies, though of sunlike magnitude, are not self-luminous. Madler 

 and Bessel embraced similar views. Those who believe, with Helm- 

 holtz, that a sun's heat and light are produced by the contraction of its 

 mass, and that solar activity has a limited duration, might be naturally 

 led to consider dark systems a hundred or even a thousand times as 

 numerous as those which are illuminated. Yet I think it more reason- 

 able to take the moderate estimate of Laplace for the comparative 

 numbers of the dark and the bright occupants of space. But it is, 

 moreover, necessary to consider that great planets and satellites meet 

 their ultimate doom by a number of dismemberments and great mete- 

 oric scenes, each separated by intervals of many millions of centiiries. 

 Taking all these circumstances into account, the age of a world, as in- 

 ferred from the observed indications of catastrophes in the heavens, 

 may reach as high as 500,000,000,000 years. 



If the feelings of some readers will revolt from the idea of having a 

 primary or even a secondary mundane orb occasionally sacrificed in 

 some part of the wide celestial domain, they must be powerfully 

 shocked by the views of Dr. Croll, who gives destruction a far more 

 oppressive sway over the great works of creation, when he regards the 

 collisions of suns as the normal means of perpetuating the economy of 

 nature. If the great centers of unfailing light were thus hurled into 

 ruin, their attendant worlds, if saved from a worse fate, would be sent 

 adrift in hyperbolic orbits and doomed to a long pilgrimage in the cold 

 interstellar regions. Without denying the possibility of such rare and 



VOL. XIT. — 31 



