the place of fire is at the centre of the universe, and that therefore the earth and other heavenly bodies move round the fiery centre.”  But this was no heliocentric system, since the sun moved, like the earth, in a circle around the central fire.  This was merely the work of the imagination, utterly unscientific, though bold and original.  Nor did this hypothesis gain credit, since it was the fixed opinion of philosophers that the earth was the centre of the universe, around which the sun, moon, and planets revolved.  But the Pythagoreans were the first to teach that the motions of the sun, moon, and planets are circular and equable.  Their idea that the celestial bodies emitted a sound, and were combined into a harmonious symphony, was exceedingly crude, however beautiful “The music of the spheres” belongs to poetry, as well as to the speculations of Plato.

Eudoxus, in the fifth century before Christ, contributed to science by making a descriptive map of the heavens, which was used as a manual of sidereal astronomy to the sixth century of our era.

The error of only one hundred and ninety days in the periodic time of Saturn shows that there had been for a long time close observations.  Aristotle—­whose comprehensive intellect, like that of Bacon, took in all forms of knowledge—­condensed all that was known in his day into a treatise concerning the heavens.  He regarded astronomy as more intimately connected with mathematics than any other branch of science.  But even he did not soar far beyond the philosophers of his day, since he held to the immobility of the earth,—­the grand error of the ancients.  Some few speculators in science (like Heraclitus of Pontus, and Hicetas) conceived a motion of the earth itself upon its axis, so as to account for the apparent motion of the sun; but they also thought it was in the centre of the universe.

The introduction of the gnomon (time-pillar) and dial into Greece advanced astronomical knowledge, since they were used to determine the equinoxes and solstices, as well as parts of the day.  Meton set up a sun-dial at Athens in the year 433 B.C., but the length of the hour varied with the time of the year, since the Greeks divided the day into twelve equal parts.  Dials were common at Rome in the time of Plautus, 224 B.C.; but there was a difficulty in using them, since they failed at night and in cloudy weather, and could not be relied on.  Hence the introduction of water-clocks instead.

Aristarchus is said to have combated (280 B.C.) the geocentric theory so generally received by philosophers, and to have promulgated the hypothesis “that the fixed stars and the sun are immovable; that the earth is carried round the sun in the circumference of a circle of which the sun is the centre; and that the sphere of the fixed stars, having the same centre as the sun, is of such magnitude that the orbit of the earth is to the distance of the fixed stars as the centre of the sphere of the fixed stars is to