Air always contains moisture, and is said to be "humid" to a greater or lesser degree. A hygrometer is an instrument to measure such humidity, which rises to 100% in mist or fog, and falls as the atmosphere dries. Various devices have been introduced to measure humidity, and three of these are represented in the Maynooth collection.

304 Daniell Hygrometer
305 Mason Hygrometer
307 Dyne's Hygrometer

Meteorology

Other Met. Instruments