In carefully tracing the conspicuous scenes which must mark the end of a planetary career, and thus obtaining a more correct interpretation of the rare and mysterious characters occasionally inscribed in our skies, very interesting information may be obtained of the diversified 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 extravagant to suppose that, in our universe, the large primary and secondary 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 immeasurable 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. According 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 Helmholtz, 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 reasonable 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 meteoric scenes, each separated by intervals of many millions of centuries. Taking all these circumstances into account, the age of a world, as inferred 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
