the conception of the
physical medium must be simple in character, its properties and motions
must agree with all our experience, as given by observation, and
experiments; and the properties and motions postulated for it must
satisfactorily account for, and explain all the phenomena that are
presented to us by the Universal Law of Gravitation.

If all this be done, then from the standpoint of strict philosophical
reasoning, the physical medium so suggested, and the theory so made,
will be incapable of being overthrown or disproved.

CHAPTER II

PHILOSOPHY OF GRAVITATION

ART. 18. _Gravitation Attraction._--The Law of Gravitation being a
compound law, and not a simple law (Art. 8), it is necessary that the
principles which govern universal attraction should now be considered.

The law which governs Gravitation Attraction may be defined as follows:
Every particle of matter in the universe attracts every other particle
with a force whose direction is that of a line joining the centre of
their masses, whose magnitude is directly as the product of their
masses, and inversely as the square of the distance between them.

This may be divided into four parts.

(1) The Universality of Gravitation.
(2) The Direction of the Forces involved.
(3) The Proportion of these Forces.
(4) The Law of Inverse Squares.

The theory of the Aether, therefore, which will be perfected in this
work, must not only satisfactorily account for the Attraction of
Gravitation on a strictly philosophical basis, but the laws, governing
the pressures or tensions of that physical medium, must harmonize with
each of the parts of the complex Law of Gravitation into which it has
been resolved.

ART. 19. _Universality of the Attractive Force._--The principle upon
which Universal Attraction rests is found in the words: "Every particle
of matter in the universe attracts every other particle." It must,
however, be admitted that this statement has never actually been proved.
The smallest body that Newton used to prove his Law of Attraction was
our satellite the moon.

Cavendish, however, in 1798, by a series of experiments, conclusively
demonstrated that the force of Gravitation existed in small bodies. He
took two small leaden balls of a certain weight, and fixed them at the
ends of a rod about six feet long, the rod being suspended by a piece of
wire in the air. Large leaden