mple Gravitation?

Gravitation is an universal force which operates throughout the length
and breadth of the entire universe, and if there be a medium which is to
Gravitation, what the Aether is to light and heat, the question at once
confronts us, as to what are the characteristics, properties, and
qualities of that universal medium, which is to form the physical basis
of this universal attraction?

Newton himself suggested that Gravitation was due to an aetherial subtle
medium, which filled all space.

In his well-known letter to Bentley, Newton writes as follows: "That
Gravity should be innate, inherent, and essential to matter, so that one
body can act upon another body at a distance through a vacuum, without
the mediation of anything else, by and through which their action and
force may be conveyed from one to another, is to me so great an
absurdity, that I believe no man who has any philosophical nature or
competent faculty of thinking can ever fall into it."

We also know from his Queries in his book on _Optics_, that he sought
for the explanation of Gravitation in the properties of a subtle,
aetherial medium diffused over the universe.

MacLaurin on this point says: "It appears from his letters to Boyle,
that this was his opinion early, and if he did not publish his opinion
sooner, it proceeded from hence only, that he found he was not able from
experiment and observation to give a satisfactory account of this
medium, and the manner of its operations in producing the chief
phenomena of Nature."

Therefore, if we accept Newton's suggestion, and endeavour to trace the
physical cause of Gravitation in the qualities, properties, and motions
of this subtle aetherial medium to which he refers, we shall be simply
working on the lines laid down by Sir Isaac Newton himself.

I wish therefore to premise, that the future pages of this work will
deal with the hypothesis of this aetherial medium, by which will be
accounted for, and that on a satisfactory and physical basis, the
universal Law of Gravitation.

ART. 3. _Rules of Philosophy._--In order that we may rightly understand
the making of any hypothesis, I purpose giving some rules laid down by
such philosophers as Newton and Herschel, so that we may be guided by
right principles in the development of this new hypothesis as to the
cause of Gravitation.

The rules that govern the making of any hypotheses, so far as I can
discern, may be summed up under the th