vintage sling psychrometer (also called a whirling hygrometer), complete with its wooden case, leather carrying pouch, and wick.

📖 What it is

• Purpose: Used to measure relative humidity by comparing the readings of a wet-bulb and a dry-bulb thermometer.

• Date: The paper tag shows a code "7-41", which likely refers to July 1941 — making this a WWII-era instrument.

• There is the top of the crown used for Military items which support the above assumption.

• Design:

  • Two thermometers mounted in a wooden frame.

  • A wick (to be moistened) goes over one bulb.

  • The handle allows it to be swung (“slung”), evaporating water to cool the wet bulb, giving a humidity reading when compared to the dry bulb.

• These were standard issue for meteorological work, aviation, and military field operations in the mid-20th century.