Reading the Skies: The Ultimate Barometer Quiz

If you see a barometer on a wall that looks like a clock, it is an 'aneroid' type, which uses mechanical parts instead of liquid mercury.

Since air pressure drops at a predictable rate as you go higher, a pilot can use a barometer to calculate exactly how far they are above sea level.

If we look at scientific history, Torricelli was the first to prove that the "weight of the air" could hold up a column of mercury, leading to the invention of the barometer in 1643.

If a tool measures heat, it is a thermometer; if it measures wind speed, it is an anemometer. Since air pressure is the weight of the air pressing down, we use a barometer to detect those changes.

Historically, scientists used mercury in a tube because it is very heavy and sensitive to pressure. Today, we also use 'aneroid' barometers, which use a small metal box that expands or contracts without using liquid.

If the air pressure increases, then it pushes harder on the surface of the mercury pool at the base. This force pushes the liquid up into the vacuum tube, showing a higher reading.

If we used water, the barometer would need to be over 30 feet tall because water is light. Since mercury is 13 times denser than water, the instrument can be small enough to fit on a wall.

If a barometer is 'aneroid,' the word literally means 'without liquid.' Instead, it uses a flexible metal capsule that changes shape based on the weight of the air outside it.

If air pressure falls, it means the air is rising and becoming less dense. Since rising air cools and allows clouds to form, a falling barometer is a classic sign of an incoming storm.

As you go higher up a mountain, there is less air above you pressing down. If there is less air weight, then there is less pressure to push the mercury up the tube, causing the reading to drop.

Scientists use 'millibars' (mb) to describe the force, or they measure the actual physical height of the mercury in the tube in 'inches' or 'millimeters.'

If a new air mass is moving into an area, the pressure will change before the rain or wind actually starts. Therefore, watching the barometer gives us a 'heads-up' that the weather is about to shift.

If the pressure is high, the air is sinking and pressing down firmly. Since sinking air prevents clouds from forming, high pressure is almost always associated with clear skies.

If the air pressure changes, then the thin metal walls of the inner cell are pushed in or allowed to pop out. This movement is connected to a needle that points to the pressure reading on the dial.

If you imagine a tall column of air reaching from the ground to space, the weight of all those gas molecules creates the force we call air pressure.

Even though air pressure is strong (about 14.7 pounds per square inch), the materials in a barometer are designed to withstand that force while still being sensitive enough to move when it changes.

If you are standing at the ocean's edge, the weight of the entire atmosphere above you averages out to 1013.2 millibars. This is the 'baseline' used by scientists.

Because air is a fluid (a gas), it exerts pressure in all directions—up, down, and sideways. This is why a barometer works regardless of how it is tilted or placed.

If you need to see the 'trend' of pressure over 24 hours, you use a barograph. It uses a pen and a rotating drum to draw a line that shows if the pressure has been rising or falling.

If there is no air, there is no pressure to push the mercury up the tube. Therefore, the mercury would simply fall into the reservoir at the bottom, leaving a reading of zero.