How Dry I Am

It began as a shop project for my grandsons. The Rittenhouse 1782 hygrometer, as shown by Roy Underhill in his Woodwrights Work Book (1986). David Rittenhouse, an instrument maker, was a contemporary of Franklin and Jefferson, and the Astronomer of the United States. The hygrometer is based on two thin strips of wood, one piece of tangential grain, the other longitudinal, glued together with the grains at right angles and mounted on a board. The difference in expansion due to humidity change causes the strips to curve, presenting a humidity measurement. 

 

Right photo, 30% RH.