Barometer

A barometer is a scientific instrument used to measure atmospheric pressure. This is the weight of the air pressing down on the Earth's surface.

By tracking these readings, scientists can observe pressure tendency. This refers to how pressure changes over a short period. These changes help meteorologists forecast upcoming weather patterns. Barometers are essential for finding surface troughs and pressure systems. They also help identify frontal boundaries in the atmosphere.

One common type is the mercury barometer. This device consists of a vertical glass tube closed at the top. The bottom of this tube sits inside an open basin filled with mercury. The atmosphere exerts force on the mercury in the basin. This force pushes the liquid up into the tube. The mercury level adjusts until it balances the atmospheric force.

When air pressure is high, the mercury rises higher in the column. When pressure is low, the mercury level drops. Scientists must also adjust the scale for temperature. Higher temperatures reduce the density of the mercury.

A barometer is different from a pressure altimeter. Both instruments use atmospheric pressure, but they serve different goals. A barometer stays at a constant altitude to measure weather changes. An altimeter measures the pressure of the surrounding atmosphere to estimate altitude. It compares the current pressure to expected levels at various heights. This allows pilots and hikers to determine how high they are.

Before the 1600s, many people believed air had no weight.

In 1630, Giovanni Battista Baliani observed a siphon experiment. He found that water could only rise to about 10 meters. Galileo Galilei suggested that a vacuum held the water up. He believed nature resisted the creation of a vacuum. Later, Gasparo Berti and Raffaello Magiotti conducted experiments with tubes. They observed that water stayed at a specific height in a tube. This suggested a vacuum might exist in the space above the water.

Evangelista Torricelli is credited with inventing the barometer around 1643 or 1644.

He proposed a revolutionary idea about the weight of the air. He argued that the atmosphere pushes on the water in a basin. This weight holds up the column of liquid in the tube. To make his tool more practical, he used mercury. Mercury is about 14 times denser than water. This meant he only needed an 80 cm tube instead of a 10.5 m tube. He demonstrated that air pressure could support 30 inches of mercury.

Other scientists worked to prove these mechanical theories. Blaise Pascal wanted to test if air pressure changed with altitude.

He asked Florin Perier to take a barometer up the Puy de Dôme mountain. In September 1648, Perier performed this experiment. He found that the mercury column stood lower at the top of the mountain. This proved that air pressure decreases as altitude increases. There is less air above the observer to provide weight.

There are many variations of barometers used today. One simple version is the "weather glass" or Goethe barometer.

It uses a sealed glass container that is half-filled with water. A narrow spout connects the body to the atmosphere. If air pressure drops, the water rises in the spout. If pressure increases, the water level drops. Modern technology also uses barometric sensors. You can find these in devices like smartphones. These sensors help gadgets calculate altitude and track weather.