Superficies. The surface of any figure. Space extended in length and width.
System. The mutual connexion, and dependance of things, upon each other. The solar, or Copernican system, includes the sun, the planets, with their moons, and the comets.
Tangent. A straight line touching the circumference of a circle; but which would not cut off any portion of it, were it extended beyond the touching point, in both directions.
Telescope. An instrument by which distant objects may be distinctly seen; the images of objects being brought near to the eye, and greatly magnified.
Temperate Zones. Those portions of the surface of the earth situated between 231/2 and 661/2 degrees of latitude. Within these boundaries, the sun is never vertical; nor does he ever remain, during a whole day, below the horizon.
Thermometer. An instrument for measuring the temperature of the atmosphere, or of other bodies.
Torrid Zone. That portion of the earth which extends 231/2 degrees on each side of the equator, to the tropical circles; within this limit, the sun is vertical, twice in the year.
Transit. Mercury or Venus, are said to transit the sun, when they pass between the earth and that luminary. They then appear like dark spots, upon the face of the sun.
Transparent. Allowing the rays of light to pass freely through. The reverse of opaque. Glass, water, air, &c. are transparent bodies.
Tropics. Two circles on the globe on either hemisphere, at the distance of 231/2 degrees from the equator. Beyond these circles, the sun is never vertical: and the countries within them, are denominated tropical.