How did meteorologists first measure the weight of the earth’s atmosphere?

What would the weather forecast be without a map of highs and lows? How could the weatherman guarantee us a sunny weekend or predict a blizzard if it weren’t for the barometer?

This instrument is undoubtedly one of the meteorologist’s most useful tools, but there’s nothing magical or complex about it, its precursor was invented over 300 years ago.

In 1644 a protégé of Galileo’s, Evangelista Torricelli, filled a glass tube with mercury and submerged one end in a basin of mercury, while keeping his finger over the other end. When he removed his finger, some of the mercury remained suspended in the tube rather than sinking to the bottom and slipping into the basin.

The reason, according to Torricelli, was that “on the surface of the liquid in the basin presses a height of 50 miles of air.” Atmospheric pressure was, in fact, keeping the mercury suspended in the tube and Torricelli watched its level change with different weather conditions.

“We live,” remarked the inventor in a reflective mood, “submerged at the bottom of an ocean of elementary air.”