Lee Valley Tools Gardening Newsletter
Vol. 4, Issue 2
April 2009
 
What Is It?
 
 
  What Is It?  
  Also called a wet-and-dry-bulb thermometer, a psychrometer is a simple type of hygrometer, an instrument that measures temperature and humidity. The psychrometer consists of two thermometers, one with a dry base and one with a wet base, mounted beside each other in a frame. The bulb of the wet thermometer is wrapped in cloth that's been soaked in water. As the water evaporates, it absorbs heat, which causes the thermometer's temperature reading to drop. The drier the air, the quicker the water will evaporate and the greater the drop in the thermometer's temperature reading. The difference in readings between the wet and dry thermometers can be used to determine the relative air humidity.

This model, made by Taylor, is called a sling psychrometer. It is held by the handle and spun around to hasten evaporation from the cloth, as demonstrated below.
 
     
  Psychrometer in motion  
     
Other Articles from this Issue
 
 
What's New in Gardening
 
Seal-a-Bag™

Seal-a-Bag™
Bubbler Spot Soaker

Bubbler
Spot Soaker
Upside-Down Sprayer

Upside-Down
Sprayer
Flexible Blossom Crown

Flexible
Blossom Crown
 
Stainless-Steel Spatula

Stainless-Steel
Spatula
WaterStik™

WaterStik™
Self-Watering Plant Tray

Self-Watering
Plant Tray
Comfort-Lock Spray Pistol

Comfort-Lock
Spray Pistol
 
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