Academic journal article The Science Teacher

Torricelli's Barometer

Academic journal article The Science Teacher

Torricelli's Barometer

Article excerpt

In 1644, Italian physicist Evan Torricelli described the world's first mercury barometer in a letter to his friend Michelangelo Ricci. Seventy-one years later (and 68 years after Torricelli died), an engraving of this barometer appeared in a book entitled Lezioni accademiche d'Evangelista Torricelli, mattematico e filosofo del Sereniso (Academic Lessons of Evangelista Torricelli, Mathematician and Philosopher of Sereniso). Behind the remarkable invention is a story of evolving scientific discourse, philosophy, and argumentation stretching back 2,000 years.

Torricelli's famous experiment was largely inspired by Tuscan well diggers, frustrated in their attempts to raise water more than 10 meters using suction pumps. Galileo himself had attempted--and failed--to explain the phenomenon successfully.

Upon Galileo's urging, Torricelli also conducted experiments to solve this riddle. In the experiment, two glass tubes were filled with mercury, inverted, and placed within a larger container of mercury. Some of the fluid drained into the container, forming vacuums at the top.

Torricelli varied the amount of space at the top of the tubes to create two different vacuums but, significantly, found that the fluid height remained the same. At the time, many scientists thought the vacuum above a column of fluid would draw up the liquid (to eliminate the unstable vacuum). The remarkable insight of Torricelli's experiment was that the vacuums didn't "pull" the fluid at all. Instead, air pressure pushed the fluid up into the space created by the vacuum. With this, not only had Torricelli explained the limitation of the suction pumps; he had revolutionized the way we view vacuums, air, and air pressure. …

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