What is a barometer and what is it for?

There are many ways to get information about the world. You can, for example, just look out your window to see what the weather is like today and whether you should bring an umbrella.

You can look at the thermometer to see how you should dress when you leave home. But we need a good barometer to find out if the weather is going to stay fine for long, or if it might rain for the next few hours.

What is a barometer?

A barometer is an instrument that measures atmospheric pressure. Above the surface of the Earth is a layer of atmosphere several tens of kilometers thick. The mixture of gases that make up the atmosphere, though light, still exerts a certain amount of pressure on the Earth’s surface in such vast quantities. We do not notice it because our bodies are well adapted to it, but the amount of atmospheric pressure can be measured.

The first measurements of atmospheric pressure were made with a very simple measuring device – a thin glass tube in which mercury was poured. Suppose the tube was 1 millimeter thick and exactly 1000 millimeters long, or 1 meter.

If you tip the tube with the sealed end vertically upwards and the open end downwards, some of the mercury will flow out and some will remain inside. The mercury will flow out until the pressure inside the tube and outside is balanced.

If you measure the height of the mercury column in the tube, you can think of this value as the atmospheric pressure. For normal weather, it is 760 millimeters of mercury column – this is the reading of the mercury barometer. Water, alcohol, etc. can be used as a liquid filling the tube, but mercury is accepted.

A more convenient and accurate reading is the so-called aneroid barometer, or anhydrous barometer. It measures pressure using a sealed box of thin tin, from which some of the air is pumped out.

Under the action of atmospheric pressure, the walls of the box sag and stretch or compress a spring, to the other edge of which an arrow is attached. The dial shows how much the atmospheric pressure has changed from the baseline.

Weather Prediction with a Barometer

From school science lessons we remember that air pressure is not a constant value – it changes depending on weather and climatic conditions. Changes in pressure in the high and low layers of the atmosphere are associated with changes in the weather.

If the weather is pleasant, warm and windless, the barometer shows high pressure. But as soon as it falls, it means that the next day will be cold or rainy.

You don’t have to have a barometer outside to predict the weather. The atmospheric pressure within your home will be exactly the same as outdoors. The number of floors in a house affects the readings a little, because even on the 12th or 25th floor, the pressure in pleasant weather will be lower than on the lower floors of the same house.

Using a barometer to determine altitude

Because the pressure of the atmospheric column decreases as you ascend upward, this property has long been used in aviation instruments that determine flight altitude. Such instruments are called altimeters.

Of course, readings of the first, still imperfect devices depended significantly on weather, because bad weather is accompanied by a drop in pressure, and therefore the device will show a higher altitude than it actually is, if no correction is made in its readings. Modern altimeters work on a different principle, not using atmospheric pressure to measure altitude.

How do I use a barometer?

Typically, a domestic barometer-aneroid is an arrow instrument with a circular or semicircular scale on which the divisions are plotted. The measurement is traditionally used in millimeters of mercury.

If the needle shows 750-760 mm Hg, you have a nice day ahead which can be devoted to a walk, a trip to nature, a trip to the countryside, etc. If the pressure has dropped below 750 mm Hg and continues to fall, it most likely means the approach of inclement weather, a sharp cold snap, and related precipitation.

Observations of atmospheric pressure are vitally important for people who suffer from high or low blood pressure. During periods of sudden drops in atmospheric pressure, such people felt their condition worsen.

Information about weather changes is important for them to have time to take their medicine in time to preserve their performance and, sometimes, their health.

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