TORRICELLIAN

, a term very frequent among physical writers, used in the phrases, Torricellian tube, or Torricellian experiment, on account of the inventor Torricelli, a disciple of the great Galileo.

Torricellian Tube, is the barometer tube, being a glass tube, open at one end, and hermetically sealed at the other, about 3 feet long, and 2/10 of an inch in diameter.

Torricellian Experiment, or the filling the baro- meter tube, is performed by filling the Torricellian tube with mercury, then stopping the open orifice with the finger, inverting the tube, and plunging that orifice into a vessel of stagnant mercury. This done, the finger is removed, and the tube sustained perpendicular to the surface of the mercury in the vessel.

The consequence is, that part of the mercury falls out of the tube into the vessel, and there remains only enough in the tube to fill about 30 inches of its capacity, above the surface of the stagnant mercury in the vessel; these being sustained in the tube by the pressure of the atmosphere on the surface of the stagnant mercury; and according as the atmosphere is more or less heavy, or as the winds, blowing upward or downward, heave up or depress the air, and so increase or diminish its weight and spring, more or less mercury is sustained, from 28 to 31 inches.

The Torricellian Experiment constitutes what we now call the Barometer.

Torricellian Vacuum, is the vacuum produced by filling a tube with mercury, and when inverted allowing it to descend to such a height as is counterbalanced by the pressure of the atmosphere, as in the Torricellian Experiment and Barometer, the vacuum being that part of the tube above the surface of the mercury.

TORRID Zone, is that round the middle of the earth, extending to 23 1/2 degrees on both sides of the equator.