What is used to assess the amount of humidity in the air?

The device used to assess the amount of humidity in the air is a hygrometer. Hygrometers measure the moisture content in the atmosphere and can be based on various principles, such as the physical changes that materials undergo relative to humidity (like hair or certain metals) or the electrical changes in materials in response to humidity levels.

Thermometers measure temperature, which, while related to weather conditions, do not provide information about humidity. Anemometers are designed to measure wind speed and direction, focusing on air movement rather than moisture content. Barometers are used to measure atmospheric pressure, assisting in weather predictions but not addressing humidity levels. Thus, the hygrometer is specifically tailored for measuring humidity, establishing it as the correct choice in this context.