Like many innovations, the air conditioner got its toehold in the market when it was embraced by an elite group of "early adopters" -- all of whom were entrepreneurs. AC was invented by Willis Haviland Carrier, founder of Carrier Corp., who reportedly had an epiphany about how to cool air while standing on a fog-shrouded train platform. He sold his first machines to a printer who wanted to rid his pressroom of paper-swelling humidity and to two candy companies that were vexed by melting chocolate during the summer. In its ninth year, 1924, Carrier's focus switched from cooling production facilities to cooling consumers. The company's "centrifugal chillers" proved welcome in a Detroit bargain basement notorious for mass fainting during sales. Then a Houston movie theater bought AC and became a refuge on stifling nights. Ticket sales soared. In the years to come, theaters nationwide would popularize air conditioning among the American public.

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