Numerous as are the heavenly bodies visible to the naked eye, and glorious as are their manifestations, it is probable that in our own system there are great numbers as yet undiscovered.  Just two hundred years ago this year, Huyghens announced the discovery of one satellite of Saturn, and expressed the opinion that the six planets and six satellites then known, and making up the perfect number of twelve, composed the whole of our planetary system.  In 1729 an astronomical writer expressed the opinion that there might be other bodies in our system, but that the limit of telescopic power had been reached, and no further discoveries were likely to be made.[A] The orbit of one comet only had been definitively calculated.  Since that time the power of the telescope has been indefinitely increased; two primary planets of the first class, ten satellites, and forty-three small planets revolving between Mars and Jupiter, have been discovered, the orbits of six or seven hundred comets, some of brief period, have been ascertained;—­and it has been computed, that hundreds of thousands of these mysterious bodies wander through our system.  There is no reason to think that all the primary planets, which revolve about the sun, have been discovered.  An indefinite increase in the number of asteroids may be anticipated; while outside of Neptune, between our sun and the nearest fixed star, supposing the attraction of the sun to prevail through half the distance, there is room for ten more primary planets succeeding each other at distances increasing in a geometrical ratio.  The first of these will, unquestionably, be discovered as soon as the perturbations of Neptune shall have been accurately observed; and with maps of the heavens, on which the smallest telescopic stars are laid down, it may be discovered much sooner.

[Footnote A:  Memoirs of A.A.S., vol. iii, 275.]

THE VASTNESS OF CREATION.

But it is when we turn our observation and our thoughts from our own system, to the systems which lie beyond it in the heavenly spaces, that we approach a more adequate conception of the vastness of creation.  All analogy teaches us that the sun which gives light to us is but one of those countless stellar fires which deck the firmament, and that every glittering star in that shining host is the center of a system as vast and as full of subordinate luminaries as our own.  Of these suns—­centers of planetary systems—­thousands are visible to the naked eye, millions are discovered by the telescope.  Sir John Herschell, in the account of his operations at the Cape of Good Hope (p. 381) calculates that about five and a half millions of stars are visible enough to be distinctly counted in a twenty-foot reflector, in both hemispheres.  He adds, that “the actual number is much greater, there can be little doubt.”  His illustrious father, estimated on one occasion that 125,000 stars passed through the field of his forty foot reflector in a quarter of an hour.  This would give 12,000,000 for the entire circuit of the heavens, in a single telescopic zone; and this estimate was made under the assumption that the nebulae were masses of luminous matter not yet condensed into suns.