ry heavens and the celestial objects mentioned in
'Paradise Lost.'

3. To exemplify the use which Milton has made of astronomy in the
exercise of his imaginative and descriptive powers.

In the earlier half of the seventeenth century the Ptolemaic theory--by
which it was believed that the Earth was the immovable centre of the
universe, and that round it all the heavenly bodies completed a diurnal
revolution--still retained its ascendency over the minds of men of
learning and science, and all the doctrines associated with this ancient
astronomical creed were still religiously upheld by the educated classes
among the peoples inhabiting the different civilised regions of the
globe. The Copernican theory--by which the Sun is assigned the central
position in our system, with the Earth and planets revolving in orbits
round him--obtained the support of a few persons of advanced views and
high scientific attainments, but its doctrines had not yet seriously
threatened the supremacy of the older system. Though upwards of one
hundred years had elapsed since the death of Copernicus, yet the
doctrines associated with the system of which he was the founder were
but very tardily adopted up to this time. There were several reasons
which accounted for this. The Copernican system was at first imperfect
in its details, and included several of the Ptolemaic, doctrines which
rendered it less intelligible, and retarded its acceptance by persons
who would otherwise have been inclined to adopt it. Copernicus believed
that the planets travelled round the Sun in circular paths. This
necessitated the retention of cycles and epicycles, which gave rise to
much confusion; nor was it until Kepler made his great discovery of the
ellipticity of the planetary orbits that they were eliminated from the
system.

As the Ptolemaic system of the universe held complete sway over the
minds of men for upwards of twenty centuries, it was difficult to
persuade many persons to renounce the astronomical beliefs to which they
were so firmly attached, in favour of those of any other system; so that
the overthrow of this venerable theory required a lengthened period of
time for its accomplishment.

It was thus in his earlier years, when Milton devoted his time to the
study of literature and philosophy, which he read extensively when
pursuing his academic career at Christ's College, Cambridge, and
afterwards at Horton, where he spent several years in acquiring a mor