This hygrometer was made in the 1950's by the Taylor Instrument Company of Rochester New York.
This brilliantly designed device is still capable of helping you accurately calculate the humidity of the air with it's simple operation. Simply fill the glass bulb with water and ensure the wick is in the bottle and attached to the thermometer on the right. Give it some time and observe the temperature reading on the two thermometers. You would then use the rotating dial in the centre to align the two temperature readings which will give you the % humidity.
In good condition, comes as shown with no box and some some of the paper has come off the rotating dial. Can still be used without the rotating chart, you can find examples of these charts online to use.
Amaze your friends with your knowledge of science, or just add another neat-o gadget to your wall.