Berti's Barometer
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Your average weather report includes things like temperature, wind speed, inches of precipitation, and sometimes something called inches of mercury, pressure. Hi, I'm Bryan Yeaton and this is The Weather Notebook.

Experiment by Gaspare Berti in the Minim Convent at Pincio. Gaspar Schott, Technica curiosa, sive, Mirabilia artis, Würzburg 1664

Three and a half centuries ago, most scientists didn't believe in the concept of a vacuum, or a place with no air. But there were a few renegade researchers who thought it could be created and one of those was Gasparo Berti.

Berti rigged up a huge glass tube, several stories high alongside his house, and filled the tube with water. Then he sealed off the top of the tube and opened the bottom into a pail full of water. He found that the water level in the tube dropped a few feet, but then didn't move. Berti claimed that he had produced a vacuum in the tube above the water line, and that's just what he did. He also made a barometer, but he didn't realize it, so it was no big deal.

But a couple years later, Evangelista Torricelli, after carefully eyeing Berti's vacuum contraption, set out to make a barometer with mercury instead of water, because Berti's barometer was just too big. The experiment was a success, and Torricelli became the creator of the barometer.

A classic mercury barometer is only about 2 1/2 feet high and much easier to deal with than Berti's water barometer which would be about the size of your average house. On a beautiful spring day, if you used Berti's barometer, the pressure would read about 30 feet, instead of 30 inches.

The Weather Notebook is a production of the Mount Washington Observatory and is supported by the National Science Foundation. To take a peek at an engraving of the experiment, apply a little pressure to your mouse and go to our website at weathernotebook.org.