telescopes, large black spots, many thousand miles in diameter, are seen upon its surface, and are evidently openings in the luminous atmosphere, through which we see the opaque solid nucleus, or the real body of the sun.

Around, and nearest the sun, at a distance of thirty-six millions of miles, revolves the planet MERCURY, with a day of twenty-four hours, and a year of eighty-eight days. Supposing the light of the sun to decrease as the square of the distance, he will receive nearly seven times as much light and heat as the earth. Through the telescope some astronomers have observed spots on his surface, and mountains several miles in height.

Next to Mercury the planet VENUS revolves at the distance of sixty-eight millions of miles, with a day of nearly twenty-four hours, and a year of 225 days. Her diameter is 7,700 miles, a little less than that of the earth. She changes her phases like the moon, exhibits spots on her surface, and, according to Schroeter, has an atmosphere and mountains nearly twenty miles in height. The light and heat which she receives from the sun is about double of that which is received by the earth.1

1 From the rare appearance and want of permanence in the spots of Mercury and Venus, Sir John Herschel is of opinion,

The next body of the Solar system is our own EARTH-our birthplace, and soon to be our grave. Its distance from the sun is ninety-six millions of miles; its equatorial diameter 7,926 miles; the length of its year 365 days six hours, and of its day twenty-four hours. The form of the Earth is that of a sphere flattened at the poles like an orange, the difference of its diameters being 261 miles. Its superficies is divided into continents and seas, the continents occupying one-third, and the seas two-thirds of its whole surface. The land, sometimes level and sometimes undulating, occasionally rises into groups and ranges of mountains, the highest of which does not exceed five miles. The Earth is surrounded with an aerial envelope or atmosphere, which is computed to be about fortyfive miles in height, though the region of clouds does not reach much above the summits of the highest mountains.

The Earth is accompanied by a MOON or satellite, whose distance is 237,000 miles, her diameter 2,160 miles, and the time of her revolution round the Earth twenty-eight days. Her surface is composed

"that we do not see as in the moon the real surface of these planets, but only their atmospheres, much loaded with clouds, and which may serve to mitigate the otherwise intense glare of their sunshine."-Outlines of Astronomy, § 509.

of hill and dale, of rocks and mountains nearly two miles high, and of circular cavities, sometimes five miles in depth, and forty in diameter, which are believed to be the remains of extinct volcanoes. She possesses neither lakes nor seas; and we cannot discover with the telescope any traces of living beings, or any monuments of their hands, though we hope that these objects will be seen with some magnificent telescope which may yet be constructed. Viewing the Earth as the third planet in order from the sun, can we doubt that it is a globe like the rest, poised in ether like them, and, like them, moving round the central luminary?

Next, beyond the Earth, is the red-coloured planet MARS, with a day of about twenty-five hours, and revolving round the sun in 687 days, at the distance of one hundred and forty-two millions of miles. His diameter is 4,100 miles, and his surface exhibits spots of different hues,—the seas, according to Sir John Herschel, being green, and the land red. The spots which have been seen on this planet by several astronomers, are not always equally distinct, but when seen "they offer," as Sir John Herschel observes, "the appearance of forms, considerably definite and highly characteristic, brought successively into view by the rotation of the planet,

from the assiduous observation of which it has even been found practicable to construct a rude chart of the surface of the planet. The variety in the spots may arise from the planet not being destitute of atmosphere and cloud; and what adds greatly to the probability of this, is the appearance of brilliant white spots at its poles, which have been conjectured, with some probability, to be snow, as they disappear when they have been long exposed to the sun, and are greatest when just emerging from the long night of their polar winter, the snow line then extending to about six degrees from the pole." In a sketch of this planet, as seen in the pure atmosphere of Calcutta by Mr. Grant, it appears, to use his words, "actually as a little world," and as the Earth would appear at a distance with its seas and continents of different shades.

Hitherto we have been surveying worlds at a respectful distance from each other, and having days, and nights, and seasons, and aspects, of the same character; but we now arrive at a region in space where some great catastrophe has taken place. At the distance of about two hundred and fifty millions of miles from the sun, corresponding to a period of about 1,500 days, astronomers long ago

1 Outlines of Astronomy, § 510.

predicted the existence of a large planet, occupying the wide space between Mars and Jupiter. In the beginning of the present century, one very small planet was discovered in this locality by M. Piazzi ; and after other two had been discovered, one by himself and the other by Mr. Harding, Dr. Olbers hazarded the opinion that the three planets were fragments of a larger one which had burst; and this remarkable theory has been almost placed beyond a doubt by the discovery, in the same place, of thirty fragments in all, chiefly by M. Gasparis of Naples, and our eminent countryman Mr. Hind, by whom no fewer than ten of these bodies have been discovered.

The following table contains the distances from the sun, and the periodic times of these remarkable bodies, the distance of the earth being unity or I,