ON THE NATURE AND PROPERTIES

OF THE AETHER.

Although ancient philosophers, especially the Aristotelians, considered the Aether to be a fifth essence—incorruptible and entirely different from the other elements—more recent thinkers, particularly the Cartesians Followers of René Descartes, who proposed a mechanical view of the universe. and the experimental physicists who followed them, recognize it as a most subtle matter that penetrates all bodies.

This Aether, as gathered from the phenomena of light and gravity, is not a solid body but a fluid and elastic one, whose particles, however minute, are in constant motion.

PROPOSITION I.

The Aether is the universal medium in which all celestial and terrestrial bodies swim.

This demonstration is clear from the fact that the space between planets is not a vacuum, but is full of a subtle matter that transmits the motion of light. For if it were a vacuum, light—which is a vibration of the aether—could not be propagated.

Newton. Princip. Lib. III.

"The Aether is not a coarse matter, but a certain most subtle spirit which penetrates through all things and exerts the forces of nature." original: "Aether non est materia crassa, sed spiritus quidam subtilissimus, qui per omnia penetrat, & vires naturae exercet."