What is "torricellian vacuum"

Torricellian \Tor`ri*cel"li*an\, a. Of or pertaining to Torricelli, an Italian philosopher and mathematician, who, in 1643, discovered that the rise of a liquid in a tube, as in the barometer, is due to atmospheric pressure. See Barometer.

Torricellian tube, a glass tube thirty or more inches in length, open at the lower end and hermetically sealed at the upper, such as is used in the barometer.

Torricellian vacuum (Physics), a vacuum produced by filling with a fluid, as mercury, a tube hermetically closed at one end, and, after immersing the other end in a vessel of the same fluid, allowing the inclosed fluid to descend till it is counterbalanced by the pressure of the atmosphere, as in the barometer.
--Hutton.

Vacuum \Vac"u*um\, n.; pl. E. Vacuums, L. Vacua. [L., fr. vacuus empty. See Vacuous.]

1. (Physics) A space entirely devoid of matter (called also, by way of distinction, absolute vacuum); hence, in a more general sense, a space, as the interior of a closed vessel, which has been exhausted to a high or the highest degree by an air pump or other artificial means; as, water boils at a reduced temperature in a vacuum.

2. The condition of rarefaction, or reduction of pressure below that of the atmosphere, in a vessel, as the condenser of a steam engine, which is nearly exhausted of air or steam, etc.; as, a vacuum of 26 inches of mercury, or 13 pounds per square inch.

   Vacuum brake, a kind of continuous brake operated by exhausting the air from some appliance under each car, and so causing the pressure of the atmosphere to apply the brakes.

   Vacuum pan (Technol.), a kind of large closed metallic retort used in sugar making for boiling down sirup. It is so connected with an exhausting apparatus that a partial vacuum is formed within. This allows the evaporation and concentration to take place at a lower atmospheric pressure and hence also at a lower temperature, which largely obviates the danger of burning the sugar, and shortens the process.

   Vacuum pump. Same as Pulsometer, 1.

   Vacuum tube (Phys.), a glass tube provided with platinum electrodes and exhausted, for the passage of the electrical discharge; a Geissler tube.

   Vacuum valve, a safety valve opening inward to admit air to a vessel in which the pressure is less than that of the atmosphere, in order to prevent collapse.

   Torricellian vacuum. See under Torricellian.