Hygrometer_Approaching_01

The atmosphere can hold a lot of water. Most of this water is in the form of a gas. How do we know exactly how much water it can hold? We find out when it becomes fully saturated. When air becomes saturated, it will eventually condense to form a liquid. This liquid may take many forms. For example, it may become snow, rain and even dew.

Think about a paper towel that gets wet. If it is just a little damp, it can hold the water. If it gets soaked, it will start to drip onto the floor. Unfortunately, this only tells us when the maximum amount has been reached. Scientists needed a way to measure exactly how much moisture is in the air.

A hygrometer is a tool used to measure the relative humidity of the air. Humidity is the percentage of water vapor, or moisture, in the air. Some hygrometers are very precise. They can tell us the exact amount of moisture in the air. Hygrometers are used in weather forecasting.

The pictures above show different types of hygrometers. The first picture is of an early version of a hygrometer. We now have digital hygrometers like the last one on the right. Can you see how they have changed over time?