On This Day in Science History - October 25 - Torricelli Barometer

October 25th marks the passing of Italian physicist, Evangelista Torricelli. He was the first to create the mercury barometer to measure air pressure. He was investigating the existence of a vacuum using mercury as a pump. He created glass tubes approximately a meter long and closed at one end which he filled with mercury. He then closed the open end with his finger and submerged the end into a bowl of mercury. When he removed his finger, the mercury in the tube would pour into the bowl and then stop suddenly near the 3/4 full mark. He reasoned the falling mercury created a vacuum inside the top of the tube and the force preventing the remaining liquid from pouring out came from the weight of the column of air above the bowl of mercury. He also noticed the level would rise and fall depending on the air pressure.

He created a useful method to measure air pressure and the non-SI unit Torr, equivalent to approximately 1 atmosphere, was named in his honor. Find out what else occurred on this day in science history.

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