;
or, to speak literally, all parabolas are similar, while there are
infinitely numerous dissimilar ellipses and dissimilar hyperbolas.
Consequently, anything coming to the Sun from a great distance must have
one exact amount of proper motion to produce a parabola: all other
amounts would give hyperbolas or ellipses. And if there are no
hyperbolic orbits, then it is infinity to one that all the orbits are
elliptical. This is just what they would be if comets had the genesis
above supposed.

* * * * *

And now, leaving these erratic bodies, let us turn to the more familiar
and important members of the Solar System. It was the remarkable harmony
among their movements which first made Laplace conceive that the Sun,
planets, and satellites had resulted from a common genetic process. As
Sir William Herschel, by his observations on the nebulae, was led to the
conclusion that stars resulted from the aggregation of diffused matter;
so Laplace, by his observations on the structure of the Solar System,
was led to the conclusion that only by the rotation of aggregating
matter were its peculiarities to be explained. In his _Exposition du
Systeme du Monde_, he enumerates as the leading evidences:--1. The
movements of the planets in the same direction and in orbits approaching
to the same plane; 2. The movements of the satellites in the same
direction as those of the planets; 3. The movements of rotation of these
various bodies and of the sun in the same direction as the orbital
motions, and mostly in planes little different; 4. The small
eccentricities of the orbits of the planets and satellites, as
contrasted with the great eccentricities of the cometary orbits. And the
probability that these harmonious movements had a common cause, he
calculates as two hundred thousand billions to one.

This immense preponderance of probability does not point to a common
cause under the form ordinarily conceived--an Invisible Power working
after the method of "a Great Artificer;" but to an Invisible Power
working after the method of evolution. For though the supporters of the
common hypothesis may argue that it was necessary for the sake of
stability that the planets should go round the Sun in the same direction
and nearly in one plane, they cannot thus account for the direction of
the axial motions.[16] The mechanical equilibrium would not have been
interfered with, had the Sun been without any rotatory movement;