How will you show that there is vacuum above the surface of mercury in a barometer? What name is given to this vacuum?

A barometer is an instrument used to measure atmospheric pressure.

Vacuum is a space devoid of matter. The barometer consists of a glass tube that has two ends one of which is closed and the other one is connected to mercury reservoir.

The mercury in the tube adjusts until the atmospheric force is balanced by the weight of mercury column. Since there is no space for air to enter the glass tube hence there is vacuum above the surface of mercury in a barometer.

This vacuum is known as Torriceilian Vacuum.