THE MILKY W AY.

91

Scene No. LXXIX. —The Origin of the Asteroids .

The existence of four planets between the orbits of Mars and Jupiter ,revolving about the sun at nearly the same distances, and differing from all theother planets in their diminutive size, and in the position of their orbits, is oneof the most singular phenomena in the history of astronomy. The disagreementof these phenomena with the regularity of the planetary distances, and with thegeneral harmony of the system, suggested to astronomers the opinion that theseirregularities were produced by some great convulsion ; and that the four smallplanets are the fragments of a larger planet, which once existed between Mars and Jupiter , and circulated round the sun nearly in the orbit of the larger ofthe four fragments (the planet Pallas). The circumstances of the new planetsfurnish many direct arguments, all concurring to shew that they have originallydiverged from one point of space, and have, therefore, been originally combinedin a larger body. It is not difficult to astronomers to ascertain, in general, theconsequences that would arise from the bursting of a planet, and to determine,within certain limits, the form and position of the orbits in which the largerfragments would revolve round the sun. Such inquiries have been instituted,and are found to coincide, very accurately, with those facts respecting the planetswhich are determined by actual observation.

In the scene, we have the sun on the right hand; on the left, the supposedoriginal planet, coloured red. In four separate orbits are shewn four fragments,such as may be imagined to result from the disruption of the central planet;each of which, when its explosive, or direct force, is balanced by its gravitationtowards the sun, begins to move in an orbit, as seen in the figure, in the case ofeach of the small spheres coloured light red.

Scene No. LXXX. —The Milky Way.

The Milky way is a luminous band, or zone, which appears to make a com-plete circle in the heavens. In our hemisphere it is seen to traverse the con-stellations Cassiopeia, Perseus, Auriga , Aries, and part of Gemini. Herschelhas determined, from numerous observations, that the brightness of the Milky way is owing, solely, to numerous small stars ; and that the closeness of thestars to each other, or what he terms their compression, increases in proportionto the brightness of the Milky way . This phenomenon, therefore, is consideredas a very extensive branching stream of many millions of stars, which, pro-bably, owes its origin to several remarkably large, as well as closely scatteredsmall stars, that may have drawn together the rest. It appears, clearly, that thestars of the Milky way are not equally distributed over it, but cluster togetherin distinct allotments ; and as there are many parts which are almost destituteof stars, it is considered that those which may once have filled these vacancies,now tbrm nebula?, or separate collections.