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A brief history of steam engines. Evangelista Torricelli 1644 The barometer. Barometer
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Barometer Torricelli's chief invention was the mercury barometer, which arose from solving a practical problem. Pump makers of the Grand Duke of Tuscany attempted to raise water to a height of 12 meters or more, but found that 10 meters was the limit with a suction pump. Torricelli employed mercury, fourteen times more dense than water. In 1643 he created a tube approximately one meter long, sealed at the top, filled it with mercury, and set it vertically into a basin of mercury. The column of mercury fell to about 76 cm, leaving a Torricellian vacuum above. As we now know, the column's height fluctuated with changing atmospheric pressure; this was the first barometer. The discovery of the principle of the barometer has perpetuated his fame ("Torricellian tube", "Torricellian vacuum"). The torr, a unit of pressure used in vacuum measurements, is named after him.
Denis Papin 1690 The first piston steam engine 1679 Steam digester (Safety valve 1695)
James Watt, as a near destitute mechanic, joined partnership with Boulton • The pair made 496 engines, relying on current developments in tool making • Some engines were still in operation for 120 years