If you can't stand the heat

It's about 137 degrees outside, but who's counting? Wait, I just made that up. It's actually 127. Thank goodness the AC is working. Here's a bit of the history of why that's so.

• In the 2nd century, a Chinese inventor, Ding Huan, devised the rotary fan. As big as six feet across and manually powered, it could cool a whole room. In British India, wealthy homes had a cloth sail called a punkah attached to the ceiling. A servant in another room, the "punkah wallah," would move the fan back and forth by means of a rope and pulleys. These methods, of course, required the poor to get hotter so that the rich might be cooler.

• In 1758, Benjamin Franklin experimented with the rapid evaporation of volatile liquids, such as alcohol and ether, to cool water to a point below freezing. He was able lower the temperature to 7 degrees Fahrenheit from 64. In a letter to a friend, Franklin wrote that the experiment showed that, scaled up, "one may see the possibility of freezing a man to death on a warm summer's day."

• Sixty years later, the great British physicist Michael Faraday demonstrated that one could use mechanical power to compress a volatile substance such as ammonia into a liquid—and then, by allowing it to rapidly evaporate, cool water.

• Soon after, John Gorrie—a young doctor living in Apalachicola, Fla.—had a problem to solve. He knew that patients were more likely to survive an illness in cool weather than in hot. So he rigged up pans full of ice near the ceiling in a hospital room. The ice would cool the air around it and, because cold air is heavier than hot air, would flow downward, over the patient and then out through holes in the room's floor. It was the first effective system of air conditioning.

• But ice was expensive in Apalachicola because it had to be imported by ship from the North, so Gorrie began to experiment with making ice by mechanical means. In 1851, he was granted a patent on a machine that worked on Faraday's principle. He quit medicine to work on perfecting his invention, but when his financial backer died he was unable to carry on and died in poverty in 1855.

Bummer.

• In 1902, Willis Carrier, a young engineer at the Buffalo Forge Company in Buffalo, N.Y., invented the first modern air conditioning, to cool a printing plant. He used a compressor to liquefy ammonia and then evaporated it to cool water. Running the water through coils, he blew air across them, cooling the air and causing it to lose moisture through condensation on the coils. The air was then ducted into the workspace.

• While useful for industrial purposes, Carrier's air-conditioning system was both large and dangerous, as ammonia is very toxic. But by the early 1920s he developed a much more efficient compressor and started using a much safer refrigerant called dielene as the volatile. (DuPont would invent Freon in 1928.)

As with all major inventions, air conditioning has had profound consequences. Washington, D.C., used to be nearly deserted in the summer because of the city's notorious heat and humidity. Today, the government runs year-round. That's not necessarily progress.