Torricelli experiment and torricelli
Torricelli experiment is one of the most important experiments in the history of people's understanding of vacuum and atmospheric pressure. The experiment, first carried out in 1643 by the Italian scientist torricelli, visually demonstrated the existence of a vacuum and measured the atmospheric pressure equivalent to that generated by a 760mm column of mercury.
To commemorate torricelli's contribution, the pressure of a 1 mm mercury column was later represented as 1 Torr. Similar to mbar, mTorr (symbol mTorr) is commonly used, 1 mTorr = 0.001 Torr. Because 1 mTorr represents the pressure of 1 micron mercury column, sometimes British and American literatures also call 1 mTorr 1 micron.
Sometimes, people will directly use the height of the mercury column or column of water to express the pressure. For example, 1mmHg means the pressure of 1mm mercury column, 1 inchHg or 1 inch of water means the pressure of 1in mercury column or column of water, and 1mm of water means the pressure of 1mm water column.