ve to modify our ideas of what
Gravitation is, if we have a mass spreading through space with mutual
attraction between its parts, without being attracted by other bodies."

We have already seen in the previous article that Faraday was of opinion
that the Law of Gravitation extended throughout the whole of the solar
system, and as Aether fills the solar system, then obviously Aether must
also be subject to the Law of Gravitation.

ART. 46. _Aether possesses Density._--That matter possesses density has
already been shown in Art. 38, and on the hypothesis that Aether is
matter, Aether must possess density also. This property has already been
postulated for the Aether, in order to account for certain phenomena in
connection with the reflection and refraction of light. Young assumed
different densities for the Aether near bodies owing to its being
attracted by those bodies (Art. 45). Reflection and refraction of light
are produced by a change of density of the Aether. It is now generally
accepted that the optical difference of bodies depends mainly on the
different densities of Aether in association with those bodies.
Professor Tyndall, in his _Lectures on Light_, writes on the density of
the Aether as follows: "The density of the Aether is greater in liquids
and solids than in gases, and greater in gases than in vacuo. A
compressing force seems to be exerted on the Aether by the molecules of
these bodies."

Apart, however, from the atomicity and gravitative properties of the
Aether, it is difficult to understand how there can be density of the
medium, and still more difficult to give a satisfactory explanation of
different degrees of density for the same medium, which some scientists
assume it to have.

If, however, all that is logically included in the statement that Aether
is matter, and therefore is atomic and gravitative, is conceded, then,
from the analogy of our own atmosphere in relation to the earth, the
density of the Aether, and different degrees of density also, is at once
put upon a logical and philosophical basis, as it is brought into
harmony with all experience and observation, and is simple in its
conception.

On the other hand, an Aether which is not atomic or gravitative cannot
possess different degrees of density, except by assuming the existence
of some unknown law of which we have no knowledge, which conception is
altogether opposed to the fundamental principles of simplicity,
observation, and