A System of Natural Philosophy - In Which the Principles of Mechanics, Hydrostatics, Hydraulics, Pneumatics, Acoustics, Optics, Astronomy, Electricity, Magnetism, Steam Engine, and Electro-Magnetism, Are Familiarly Explained, and Illus... #224498

1. A body is any substance of which we can gain a knowledge by our senses. Hence air, water, and earth, in all their modifications, are called bodies.<br><br>2. There are certain properties which are common to all bodies. These are called the essential properties of bodies. They are Impenetrability, Extension, Figure, Divisibility, Inertia, and Attraction.<br><br>3. Impenetrability. - By impenetrability, it is meant that two bodies cannot occupy the same space at the same time, or, that the ultimate particles of matter cannot be penetrated. Thus, if a vessel be exactly filled with water, and a stone, or any other substance heavier than water, be dropped into it, a quantity of water will overflow, just equal to the size of the heavy body. This shows that the stone only separates or displaces the particles of water, and therefore that the two substances cannot exist in the same place at the same time. If a glass tube open at the bottom, and closed with the thumb at the top, be pressed down into a vessel of water, the liquid will not rise up and fill the tube, because the air already in the tube resists it; but if the thumb be removed, so that the air can pass out, the water will instantly rise as high on the inside of the tube as it is on the outside. This shows that the air is impenetrable to the water.<br><br>4. If a nail be driven into a board, in common language, it is said to penetrate the wood, but in the language of philosophy it only separates, or displaces the particles of the wood.