As U.S. cities are experiencing some of the warmest temperatures on record, it's easy to take for granted the ability to feel almost instant relief from oppressive heat with the push of a button or the flip of a switch. Today about 87 percent of U.S. households have an air conditioning unit.
But at the turn of the 20th century, when Willis Carrier of New York invented the first modern electrical air conditioning unit, the goal wasn't to keep homes and offices cool on hot summer days. Rather, the device became popular with industries from textiles to cotton to tobacco. It wasn't until some decades later that human comfort became an important use, especially in the South; first with air-conditioned movie theaters and then in department stores.