Hygrometers & Psychrometers
There’s a great article on Wikipedia that goes to the various aspects of moisture measurement in air at http://en.wikipedia.org/wiki/Hygrometer
On the nest few pages is a copy of the article as of January 2, 2010. The text is mostly unchanged, but the layout, the paragraph sizes are reduced and some of the text relating to historic details have been omitted to make it easier to read online.
