Evangelista Torricelli is credited with inventing the barometer in 1643. He was born on October 15 1608 in Italy, and died on October 22 1647. He was a mathematician and a physicist, and he worked at one stage with Galileo. Torricelli filled a long glass tube with mercury and inverted the tube in a dish to create the design of the barometer (see figure below). He noticed that the height of the mercury varied from day to day, and that this was likely to represent the variation in the atmospheric pressure. He built the first barometer with mercury in about 1944.

Figure of a Torricelli Barometer - showing inverted sealed tube. Torricelli noted from this experiment that the pressure of the atmosphere is about 76 centimetres, or 760 mmHg (which is "atmospheric pressure").