Italian physicist who served as the secretary and companion of Galileo during the last three months of his life.  In investigating vacuums, he constructed the first mercury barometer  in 1643-1644.  He correctly attributed the fact that the height of the mercury was only 1/14 that of a water barometer to the fact that mercury is fourteen times as dense as water. He also noticed that the level of mercury varied from day to day, and observed that the space above the mercury in the barometer must contain a vacuum.

Torricelli also developed the concepts of momentum  and impetus, and solved Fermat's Triangle problem for the Torricelli Point.