Attraction. A tendency in bodies to approach each other, and to exist in contact.
Attraction of Cohesion. That attraction which causes matter to remain in masses, preventing them from falling into powder. For this attraction to exist, the particles must be contiguous.
Attraction of Gravitation. By this attraction, masses of matter, placed at a distance, have a tendency to approach each other. Attraction is mutual between the sun and the planets.
Axis of the Earth, or of any of the planets. An imaginary line passing through their centres, and terminating at their poles; round this their diurnal revolutions are performed.
Axis of Motion. The imaginary line, around which all the parts of a body revolve, when it has a spinning motion.
Axis of a Lens, or Mirror. A line passing through the centre of a lens, or mirror, in a direction perpendicular to its surface.
Balloon. Any hollow globe. The term is generally applied to those which are made to ascend in the air.
Barometer. Commonly called a weather-glass. It has a glass tube, containing quicksilver, which by rising and falling, indicates any change in the pressure of the atmosphere, and thus frequently warns us of changes in the weather.
Body. The same as Matter. It may exist in the solid, liquid, or æriform state; and includes every thing with which we become acquainted by the aid of the senses.
Burning-glass, or Mirror. A lens, or a mirror, by which the rays of light, and heat, are brought to a focus, so as to set bodies on fire.