Before the widespread use of air conditioning, and for a long time afterwards, most Tucson homes were topped with evaporative coolers, commonly called “swamp coolers” because they chill the dry desert air by absorbing heat in water dripping through pads.

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An excelsior of shaved aspen was the traditional medium for the pads but various materials are now used.

The swamp cooler makes it possible to stay cool and moist during the hot, dry days of Tucson’s “first summer” in May and June. When the monsoon comes in July, bringing moister air, they don’t work so well.

Some Tucsonans still can’t give them up, though 99 percent of newer homes now feature air conditioning.