perhaps may be decided next lunation. The third shews an actual eruption of fire, or luminous matter." On the following day the volcano was burning with greater violence than the night before, and he found it equal to twice the size of the second satellite of Jupiter, and consequently, above three miles in diameter. Sir William observed that the eruption resembled a piece of burning charcoal. The existence of recent volcanoes may therefore be considered as a proof that the moon has an atmosphere.

Although Sir John Herschel broadly asserts, that in the occultations of stars and planets by the moon, there is no appearance whatever of an atmosphere; yet we have many facts which stand in direct opposition to this statement. Cassini assures us, that he frequently observed the circular figure of Jupiter, Saturn, and the fixed stars changed into an elliptical one, when they approached either the dark or the illuminated limb of the moon. Mr. Dunn saw Saturn and his ring emerge from the moon's limb like a comet; and M. Schroeter of Lilienthal, with fine telescopes, observed "several obscurations

and returning serenity, eruptions, and other changes in the lunar atmosphere. The same astronomer discovered the twilight of the moon at the extremity of its cusps, and he found by measurement, that the inferior or more dense part of the moon's atmosphere was not above 1500 feet, or the third of a mile high, while the height of the atmosphere where it could affect the brightness of a fixed star, is not above 5742 feet, or not much more than a mile. Hence we see the reason why changes are only occasionally produced upon stars occulted by Her atmosphere is greatly lower than her mountains. When the stars, therefore, enter, or emerge from, behind mountains higher than her atmosphere, they are not affected by refraction; and when behind mountains or level plains lower than her atmosphere, they are af fected by the refraction of the superincumbent air.

the moon.

It is evident, therefore, from all these facts, that in her volcanoes, active and extinct, in her twilight, and in her action upon immerging and emerging stars, the moon exhibits such proofs of an atmosphere, that we have a new

ground from analogy for believing that she either has inhabitants, or is in a state of preparation for receiving them.

Had the moon been destined to be merely a lamp to our earth, there was no occasion to variegate its surface with lofty mountains and valleys and extinct volcanoes, and cover it with large patches of matter, that reflect different quantities of light, and give its surface the appearance of continents and seas. It would have been a better lamp had it been a smooth sphere of lime or of chalk. The existence of extinct volcanoes, the upheaval of lofty mountains, are proofs of a progression in its physical history— of a preparation, perhaps long ago made, for the reception of inhabitants. That it is not now preparing may be inferred from the absence of

every appearance of change, since its surface has been studied by astronomers.

If it is probable, then, that the moon is inhabited, the same degree of probability may be extended to all the other satellites of the system. Their great distance from the earth prevents us from examining their surface; but even without any indication of mountains and valleys, or of

any forces that have disturbed or are still disturbing their surface, analogy compels us to conclude, that like all other material spheres, they must have been created for the double purpose of giving light to their primary planets, and a home to animal and intellectual life.

CHAPTER VI.

THE MOTION OF THE SOLAR SYSTEM ROUND A DISTANT

CENTRE.

HAD our Sun, with all the planets and comets which he controls, been absolutely fixed in space, our system could have had no connexion with the other systems of the universe. The immense void which separates it from the stars, would have been regarded as the barrier which confined it. Astronomers, however, have not only placed it beyond a doubt that the Solar system is advancing in absolute space, but have determined the direction in which it moves, and within certain limits the velocity of its motion. This great cosmical truth, the grandest in astronomy, will furnish us with a new argument for a plurality of worlds.

The first astronomer who suggested the idea of such a motion, was the celebrated Dr. Halley,1

1 Phil. Trans., 1718, No. 355, i. v. vi.