Instruments to Measure Humidity
A whirling psychrometer is a type of hygrometer which can be whirled around like a football rattle to take readings.

You can buy a simple dial humidity gauge, slightly less accurate, which uses a strip of paper responding to changes in moisture and you can directly read off the percentage relative humidity. It is a good idea to wrap it in a damp cloth for a while and then set the dial to read 100%.

Human Hair can be Used
Like paper, human hair stretches when moist and shrinks when dry. Humidity recorders use this principle, and you can make a simple hygrometer using this method.