briefly described, and to which Milton so exquisitely alludes in the following lines:

First in his East the glorious lamp was seen,
Regent of day, and all th' horizon round
Invested with bright rays, jocund to run

His longitude through Heaven's high road; the gray
Dawn, and the Pleiades* before him danced,
Shedding sweet influence : less bright the moon,
But opposite in levell'd West was set

His mirror, with full face borrowing her light
From him; for other light she needed none
In that aspect, and still that distance keeps
Till night; then in the East her turn she shines,
Revolved on Heaven's great axle, and her reign
With thousand lesser lights dividual holds,
With thousand thousand stars, that then appear'd
Spangling the hemisphere: then first adorn'd
With their bright luminaries that set and rose,
Glad evening and glad morn crown'd the fourth day.
Par. Lost. b. vii.

* Seven small stars clustered together in the constellation Taurus. These stars rise with the sun about the time of Spring, and our poet, in this passage, intimates the old and common opinion that the Creation took place in the Spring.

15

CHAPTER II.

THEORIES TO EXPLAIN THE MOTIONS OF THE HEAVENLY BODIES.

PTOLEMY.

COPERNICUS.

TYCHO BRAHE. NEWTON. A POPULAR VIEW OF THE THEORY OF GRAVITATION.

IN very early ages, before Europe occupied a page in the history of nations, the phenomena of the heavens were studied with great attention by several nations of the East. The Chaldeans, the Indians, the Chinese, and the Egyptians, have all left evidences of the industry and ingenuity with which their observations were conducted. They constructed observatories, invented instruments for observing and measuring with accuracy, -separated the stars into different groups, called Constellations, for the facility of finding any individual star,-gave particular names to most of the moving stars or planets, and noted the period which each took to move through its apparent path in the heavens; and, in many other ways, the ancients helped to lay the foundation of that mass of astronomical knowledge which the men of later ages have brought to more maturity.

Various opinions were formed respecting the motions of the Sun, Moon, and stars of all kinds, both with reference to one another, and also to the Earth; but the first theory which had attained a name and an importance in the early ages of the world, was that of Ptolemy, a distinguished Egyptian astronomer, who lived about one hundred and thirty years after the birth of Christ. He conceived that the various bodies which had been

distinguished by the appellation of "the heavenly host," were disposed in the order represented in the annexed diagram.

He supposed, according to the popular opinion, that the Earth was fixed as the centre of the universe, and that the Sun, Moon, Planets, and Stars, revolved round it in the following order; namely the Moon, Mercury, Venus, Sun, Mars, Jupiter, and Saturn; the Moon being the nearest, and so on; exterior to all of which, he supposed that a great concave sphere in which all the stars were fixed, kept on revolving round the Earth. From the early history of Astronomy, we learn that before the time of Ptolemy it had been conjectured by some that the Earth passed round the Sun, and not the Sun round the Earth; but the difficulty of believing a statement so contrary to appearances and to the evidence of one's physical senses, led to the rejection of this opinion; and although it was afterwards found to be correct, yet nearly two thousand years elapsed before such a theory was generally admitted by philosophers.

After Ptolemy had promulgated the theory which bears his name, he found that there were certain difficulties which followed from the adoption of it. He conceived that the seven bodies mentioned before which revolved round the Earth, moved in the same general direction from west to east. But on watching the progress of some of the planets, he found that they did not appear to travel uniformly round the Earth, but seemed to have, at certain times, a retrograde or opposite motion, with reference to the other planets; while at other times they seemed to be stationary. To account for this, he was obliged to suppose that those