Having filled a glass tube about a meter long, sealed from one end with mercury, Torricelli closed the other end, turned the tube upside down, and dipped it into a cup of mercury. When he opened the lower end of the tube, not all of the mercury poured out of it; a column of mercury with a height of about 760 mm remained in the tube. Torricelli realized that the mercury is held in the tube by atmospheric pressure, which presses on the surface of the mercury in the cup.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.