The Amateur Scientist; June 1998; Scientific American Magazine; by Carlson; 3 Page(s)

Depending on where you live, you may already contemplate humidity more than you care to. In the U.S., for instance, the hot summer air across the Southeast is thick and oppressive, whereas in the western deserts it is so dry that it greedily soaks up all moisture. The differences in the wildlife inhabiting these two regions shows that humidity has deeper consequences than just the daily weather. The water content in the atmosphere has shaped evolution every bit as much as the water content in the ground, which suggests many fascinating avenues for exploration by amateur scientists.

But whether your interests are in meteorology or biology, to undertake amateur investigations of humidity you'll need some means to measure it. This column describes a way to monitor relative humidity, which is the ratio of the amount of water actually present in the atmosphere to the maximum amount that it could support at the prevailing temperature and pressure.