do they owe their origin to some
unknown law? In any event, how chanced it that all were projected in
nearly the same plane as we now find them?

LAPLACE AND THE NEBULAR HYPOTHESIS

It remained for a mathematical astronomer to solve these puzzles. The
man of all others competent to take the subject in hand was the French
astronomer Laplace. For a quarter of a century he had devoted his
transcendent mathematical abilities to the solution of problems of
motion of the heavenly bodies. Working in friendly rivalry with his
countryman Lagrange, his only peer among the mathematicians of the age,
he had taken up and solved one by one the problems that Newton left
obscure. Largely through the efforts of these two men the last lingering
doubts as to the solidarity of the Newtonian hypothesis of universal
gravitation had been removed. The share of Lagrange was hardly less than
that of his co-worker; but Laplace will longer be remembered, because
he ultimately brought his completed labors into a system, and,
incorporating with them the labors of his contemporaries, produced
in the Mecanique Celeste the undisputed mathematical monument of the
century, a fitting complement to the Principia of Newton, which it
supplements and in a sense completes.

In the closing years of the eighteenth century Laplace took up the
nebular hypothesis of cosmogony, to which we have just referred, and
gave it definite proportions; in fact, made it so thoroughly his own
that posterity will always link it with his name. Discarding the crude
notions of cometary impact and volcanic eruption, Laplace filled up the
gaps in the hypothesis with the aid of well-known laws of gravitation
and motion. He assumed that the primitive mass of cosmic matter which
was destined to form our solar system was revolving on its axis even at
a time when it was still nebular in character, and filled all space to
a distance far beyond the present limits of the system. As this vaporous
mass contracted through loss of heat, it revolved more and more swiftly,
and from time to time, through balance of forces at its periphery, rings
of its substance were whirled off and left revolving there, subsequently
to become condensed into planets, and in their turn whirl off minor
rings that became moons. The main body of the original mass remains in
the present as the still contracting and rotating body which we call the
sun.

Let us allow Laplace to explain all this in detail:

"In ord