How to Read a Barometer

A barometer is a device that measures changes in atmospheric pressure. It accomplishes this by containing a small quantity of a material, generally mercury, water or even air, in a sealed vessel. Movement of this material is then caused by changes in atmospheric pressure. The reading of a barometer allows one to gain knowledge about upcoming weather patterns, which can be indirectly detected by changes in pressure.

Things You'll Need

• Barometer

Instructions

1. Examine the type of barometer you have. In most cases, you will see one long tube and one shorter, smaller tube. The smaller tube is generally air-permeable; it is designed so that the mercury or water in the barometer cannot escape but air can enter. As the air pressure surrounding the tube increases, it forces air into the smaller tube. This increase in air forces the mercury down the smaller tube and up the taller tube. This allows you to see the increase in air pressure.

2. Record the initial starting point of the mercury for a particular day; this is important because you need to know the air pressure at the start of the day so that you can see how the pressure is changing.

3. Observe the barometer frequently throughout the day to determine what the weather is doing and make notations on a sheet a paper of the changes. This is essential, because small changes in pressure can be caused by a wide variety of weather conditions. What you are looking for with the data is a large trend in either direction, especially if the trend happens quite rapidly.

4. Analyze the data with respect to common meteorological conditions. When the atmospheric pressure is falling rapidly (that is, the mercury level is going down), this may be a sign that some sort of thunderstorm activity is probable in your area. For the opposite indication when the pressure is rising, you can assume calm or stable weather patterns are approaching.