A couple of young mothers brought their children to the park last week, on a very hot day. Park workers had set out sprinklers to water some of the very thirsty plants. The children ran in and out, under the arching cascade of drops, screaming with delight and the joy of being free to race around. The smallest boy was fascinated by the way the water ran through his toy truck. He studied the gush of water with the intensity of a physics professor on the cusp of a new breakthrough. And I am sure he was ready for his nap later.