id great service to a later age in preserving
fragments of the older discoveries. The curtains were once more drawn
about the earth. The glimpses which adventurous Greeks had obtained of
the great outlying universe were forgotten for a thousand years. The
earth became again the little platform in the centre of a little world,
on which men and women played their little parts, preening themselves on
their superiority to their pagan ancestors.

I do not propose to tell the familiar story of the revival at any
length. As far as the present subject is concerned, it was literally
a Renascence, or re-birth, of Greek ideas. Constantinople having been
taken by the Turks (1453), hundreds of Greek scholars, with their old
literature, sought refuge in Europe, and the vigorous brain of the young
nations brooded over the ancient speculations, just as the vigorous
young brain of Greece had done two thousand years before. Copernicus
(1473-1543) acknowledges that he found the secret of the movements
of the heavenly bodies in the speculations of the old Greek thinkers.
Galilei (1564-1642) enlarged the Copernican system with the aid of the
telescope; and the telescope was an outcome of the new study of optics
which had been inspired in Roger Bacon and other medieval scholars by
the optical works, directly founded on the Greek, of the Spanish Moors.
Giordano Bruno still further enlarged the system; he pictured the
universe boldly as an infinite ocean of liquid ether, in which the
stars, with retinues of inhabited planets, floated majestically. Bruno
was burned at the stake (1600); but the curtains that had so long been
drawn about the earth were now torn aside for ever, and men looked
inquiringly into the unfathomable depths beyond. Descartes (1596-1650)
revived the old Greek idea of a gradual evolution of the heavens and the
earth from a primitive chaos of particles, taught that the stars stood
out at unimaginable distances in the ocean of ether, and imagined the
ether as stirring in gigantic whirlpools, which bore cosmic bodies in
their orbits as the eddy in the river causes the cork to revolve.

These stimulating conjectures made a deep impression on the new age.
A series of great astronomers had meantime been patiently and
scientifically laying the foundations of our knowledge. Kepler
(1571-1630) formulated the laws of the movement of the planets; Newton
(1642-1727) crowned the earlier work with his discovery of the real
agency that s