A barometer is a weather instrument that give you insights in atmospheric pressure. Scientists use water, air, or mercury to determine air pressure in a specific environment. Meteorologists mainly use the mercury and aneroid barometers, but we start off with the water barometer.
The water barometer
Why start with the water barometer when mercury and aneroid barometers are mainly used? Because the water barometer is the first of its kind. There are conflicting reports on who invented the first barometer. Either Torricelli or Berti, There are indications that the Italian born Gasparo Berti, accidentally created a water barometer between 1640 and 1643. And although it didn’t work as expected, it was still a barometer..
Giovanni Battista Baliani sought out Galileo Galilei seeking his opinion for the failure. Galileo felt that the water was being held up by the vacuum. Since the siphon was at the top of the hill, the height of the water became unmanageable, and so it was impossible to determine the pressure of water.
Galileo suggested the use of something else, other than the siphon, to create a vacuum. In 1638, Gasparo Berti and Raffaele Magiotti tried to find alternative ways to create the required vacuum. Berti chose to use a long tube that was plugged on both ends. He then placed the tube in a basin of water. He then opened the bottom end. Some of the water in the tube flowed out, while some was left behind. The space left at the upper part of the tube was free of air and illustrated the possibility of a vacuum existing above water.
Torricelli disagreed with the argument that the air above the water had no weight. He believed the weight of the vacuum was pressing on the water that remained in the tube. Instead of water, he felt a denser liquid, mercury, would work better than water. This made it possible for him to use a shorter tube (80cm).
Some of the scientists that built on Torricelli’s theory and the mercury barometer include Blaise Pascal and Pierre Pettit. After carrying out several experiments, the duo discovered that Torricelli was right, the air had weight. He used the mercury barometer in places with various heights. In 1648, it was confirmed that the mercury level in the barometer was lower when used on higher ground.
The mercury barometer
The traditional mercury barometer was invented by Evangelista Torricelli, an Italian physicist and mathematician, in 1643. It was referred to as the Torricellian barometer. Torricelli was a student of Galileo’s. His barometer was a simple one. He used a tall tube that was closed on one side. He filled it mercury, inverted it, and then placed it in a bowl.
When the air pressure was high, the mercury rose higher in the tube. Before turning over the tube, Torricelli put his finger on the tube to prevent air from entering the tube. This was the first time a vacuum was created in the laboratory.
Although the mercury barometer was found to be reliable and accurate, some scientists were worried about the use of mercury since it is poisonous. The aneroid barometer was invented by Lucien Vidi, a French scientist in 1844. This barometer does not use a liquid as the earlier barometers. Instead, a small metal box made from an alloy of copper and beryllium is used. This barometer has a glass face. A needle inside the barometer keeps changing based on air pressure at the time of the reading.
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To find out the air pressure, all that was required was for one to tap on the glass face. When the needle moves clockwise, the pressure is high. If, on the other hand, the needle moves anti-clockwise, the pressure is falling. The next time the pressure is checked, the needle will be in the same position it was during the last reading. For a new reading, all one needs to do is tap the glass face.