I've used the term "swamp cooler" regularly this summer (see "Enough Already" post), but never really thought about what one is until one of my kids asked. I was embarrassed to say, "Something they used on M*A*S*H," so I stuck with "I don't know, I'll look it up." I did, and now I know what one is when I say I'd rather add a swamp cooler to the house than an air conditioner. Which I might do if the summers stay as hot as this one was.
According to WonderQuest, "a swamp cooler (more formally called an evaporative cooler) is essentially a large box-like frame containing a big fan and walled in by water-wetted pads, usually made of cedar shavings or cellulose. The fan whooshes the hot outside air through the dripping pads (which are continually soaked by a water pump), cooling the air by about 20 ºF as the air evaporates water molecules from the pads. The fan then blows the water-cooled air through the house and out a deliberate vent." They work well where there is low humidity and "are popular in the southwest because they are relatively inexpensive, use a quarter as much electricity as a refrigerated unit, are easy to maintain by the average do-it-yourselfer, and add a comfortable level of humidity to the dry desert air. "