mark the progressive development of suns and systems? The genius of Herschel has effected this wonderful achievement, and explained the successive changes by which suns and worlds are formed, through the agency of the eternal and unerring laws of the Almighty. By laborious and unremitting observations, that illustrious philosopher, and his highly gifted son, have demonstrated the progress of nebular condensation,—not indeed from the appearances presented by a single nebula, (for the process, probably, can only become sensible through the lapse of hundreds, or thousands, of years,) but by observations on the almost endless series of related, contemporaneous objects in every varied state of progression, from that of a cloud of luminous vapour, to the most dense and mighty orbs that appear in the firmament. As the naturalist in the midst of a forest is unable by a glance to discover that the trees around him are in a state of progressive change; yet perceiving that there are plants in different stages of growth, from the acorn just bursting from the soil to the lofty oak that stands the monarch of the woods, can readily, from the succession of changes thus at once presented to his view, ascertain the progression of vegetable life, although extending over a period far beyond his own brief existence :-in like manner, the astronomer, by surveying the varied condition of the heavenly bodies around him, can, by careful induction, determine the nature of those changes, which,

as regards a single nebula, the human mind might otherwise be unable to ascertain.* Thus Herschel has traced from nebular masses of absolute vagueness, to others which present form and structure, the effects of the mysterious law which governs the stupendous stellular phenomena that are constantly taking place.

21. DIFFERENT STATES OF NEBULE.-Some of

*Sir John Herschel states, that the only change in a nebula which he has yet observed, is in that of Orion. A small transverse strip, which when he first figured that nebula was straight, had become curved, and showed a knotty appearance, which it did not before possess.-Athenæum, No. 565, p. 596.

while many seem assuming a spheroidal figure. Others again present a dense central nucleus of light surrounded by a luminous halo; and a series may thus be traced, from clusters of round bodies with one or more increased points of condensation, or of central illumination, to separate nebulæ with single nulcei, and with rings, to a central disk constituting a nebular star-and finally to an orb of light with a halo like the sun!

In the comets, those nebular bodies which belong to our own and other systems, we have evidence that even in the most diffused state of the luminous

matter, the masses which it forms are subservient to the laws of orbicular motion; of this fact an

interesting proof is afforded by Encke's comet, that mere wisp of vapour, which in a period but little exceeding three years, revolves around the central luminary of our system.

This beautiful theory of Herschel, and La Place, explains by an easy and evident process the formation of planets and satellites, and accounts for the uniform direction of their revolutions. And not only is it believed that such is the law which the Creator has established for the maintenance and government of the universe, but it is satisfactorily shown, upon mechanical principles, that such nebulæ must of necessity produce planetary bodies.

22. FORMATION OF THE SOLAR SYSTEM.-In our own system, the sun is a planetary orb with a luminous atmosphere, the central nucleus of a once extensive nebulosity. During the condensation of this nebula the planets were successively thrown off; the most distant, as Herschel, being the first or most ancient, followed by Saturn, Jupiter, the four asteroids, Mars, the Earth, Venus, and Mercury; the satellites, as distinct worlds, being the most recent of the whole. It is inferred, that in any given state of the rotating solar mass, the outer portion or ring might have its centrifugal force exactly balanced by gravity; but increased rotation would throw off that ring, which might sometimes retain its figure, of which we have a beautiful example in Saturn. This result, however,

could not take place unless the annular band were of uniform composition, which would rarely be the

case; hence the ring would most generally divide into several portions, which might sometimes be of nearly equal bulk, as in the asteroids; while in others they might coalesce into one mass. The solar nebulæ, thus separated at various periods, and constituting planets in a gaseous state, would necessarily have a rotatory motion, and revolve in varying orbits around the central nucleus; and as refrigeration and consolidation proceeded, each might project entire annuli or rings, and satellites, in like manner as the sun had thrown off the planets themselves.

In addition to the appearances presented by the nebulæ of various states of attenuation and of