he cloudy luminosity of the Milky Way had been resolved into a
multitude of separate stars, disclosing the immensity of the stellar
universe.

The crescent form of the planet Venus, the satellites of Jupiter and of
Saturn, and the progressive motion and measurement of light, had also
been discovered. Observations were made of transits of Mercury and
Venus, and refracting and reflecting telescopes were invented.

The law of universal gravitation, a power which retains the Earth and
planets in their orbits, causing them year after year to describe with
unerring regularity their oval paths round the Sun, was not known at
this time. Though Newton was born in 1642, he did not disclose the
results of his philosophic investigations until 1687--thirteen years
after the death of Milton--when, in the 'Principia,' he announced his
discovery of the great law of universal gravitation.

Kepler, though he discovered the laws of planetary motion, was unable to
determine the motive force which guided and retained those bodies in
their orbits. It was reserved for the genius of Newton to solve this
wonderful problem. This great philosopher was able to prove 'that every
particle of matter in the universe attracts every other particle with a
force proportioned to the mass of the attracting body, and inversely as
the square of the distance between them.' Newton was capable of
demonstrating that the force which guides and retains the Earth and
planets in their orbits resides in the Sun, and by the application of
this law of gravitation he was able to explain the motions of all
celestial bodies entering into the structure of the solar system.

This discovery may be regarded as the crowning point of the science of
astronomy, for, upon the unfailing energy of this mysterious power
depend the order and stability of the universe, extending as it does to
all material bodies existing in space, guiding, controlling, and
retaining them in their several paths and orbits, whether it be a tiny
meteor, a circling planet, or a mighty sun.

The nature of cometary bodies and the laws which govern their motions
were at this time still enshrouded in mystery, and when one of those
erratic wanderers made its appearance in the sky it was beheld by the
majority of mankind with feelings of awe and superstitious dread, and
regarded as a harbinger of evil and disaster, the precursor of war, of
famine, or the overthrow of an empire.

Newton, however, was able to