An Italian physicist and mathematician, Torricelli served as secretary to Galileo during the last three months of Galileo’s life. Two years later, pursuing a suggestion by Galileo, he filled a glass tube with mercury and inverted the tube into a dish. He noted that some of the mercury did not flow out and that the space above the mercury was a vacuum. He concluded that the variation of the height of the mercury from day to day was caused by changes in atmospheric pressure. What had he invented? Discuss