Air conditioning boosts man’s efficiency no less than his comfort. Air-conditioned homes, offices, and factories unmistakably raise human productivity and reduce absenteeism, turnover, mistakes, accidents and grievances, especially in summer. Accordingly, many employers every year cool workrooms and offices to raise summer profits. Employees in turn find cool homes enhancing not only comfort and prestige but also personal efficiency and income. With such economic impetus, low-cost summer cooling must irresistibly spread to all kinds of occupied buildings. Refrigeration provides our best cooling, serving well where people are closely spaced in well-constructed, shaded, and insulated structures. However, its first and operating costs bar it from our hottest commercial, industrial, and residential buildings. Fortunately, evaporative cooling is an economical substitute in many regions. First used in Southwest homes and businesses and in textile mills, it soon invaded other fields and climates. In 1946, six firms produced 200,000 evaporative coolers; in 1958, 25 firms produced 1,250,000, despite the phenomenal sale of refrigerating window air conditioners. Though clearly secondary to refrigeration, evaporative cooling is 60 to 80 percent is economical for moderate income groups and cheaper to buy and operate. Thus, it climates where summers are short. Moreover, it cheaply cools hot, thinly constructed mills, factories, workshops, foundries, powerhouses, farm buildings, canneries, etc., where refrigerated cooling is prohibitively expensive.