Augustin Mouchot was far from the first to realize that the sun's energy could be tapped. For more than two thousand years Chinese architects had been aligning windows and doors with the southern sky to let sunlight flood into rooms during winter, heating cold interiors. Thousands of miles away, Greek savants expounded the same architectural principles to their disciples. So, later, did the Romans, according to the solar-energy chronicler John Perlin, whose work I am drawing upon here. To heat the rooms in public baths, Romans built giant south-facing windows--those in Pompeii's caldarium were 6'7 x 9''10.