1. By your gracious, amazing, everso handsome Mr. Harris

2.  Have you ever been playing or working outside right before school started back? Have you ever felt muggy, like you couldn’t breathe because the air was so thick?  When you did simple tasks such as walking from place to place and moisture formed on your skin. It wasn’t sweat, it was water vapor in the air around you. The amount of water vapor in the air is known as Humidity.

3.  Humidity is the amount of water vapor in the air.  Humidity depends on the temperature.  The warmer the air the more water vapor it can hold, the cooler the temperature the less vapor held.  This graph shows how the amount of water vapor increases as temperature increases.

4.  Just because the temperature is high doesn’t mean that water vapor is going to fill all of the spaces that are available for it.  When air holds all the water it can at a certain temperature it is saturated.  Relative humidity is the amount of water vapor in the air compared to the maximum amount of water the air can hold at a certain temperature.  It is given as a percentage.  Saturated air has 100% relative humidity. This means we are going to have some type of precipitation.

6.  We measure relative humidity using a psychrometer. It is an instrument with two thermometers. One has a wet bulb and the other has a dry one.  For a psychrometer, the difference in temperature between the two bulbs shows how much water vapor is actually in the air.

7.  A sling psychrometer is used like it says: it is twirled in a circle for roughly 5 minutes. The wet bulb is wrapped in a damp fabric while the dry bulb stays dry.

8.  Digital psychrometers are the way of today. They are set in a specific area and can get an accurate reading without the wear and tear on your arm muscles.

9.  Wrapup review: Gimme 5 from what you have read on p. 486-485.  Make sure that the SR is complete.