Over the course of this afternoon gravity has cajoled, lured, then tugged billions of snowflakes down from a solid gray sky. Instead of appreciating the strength of this attraction I find myself remembering the advice a high school English teacher once gave me, back in the 1980s. During class there was the Robert Frost poem, then Jack London's short story, To Build a Fire , about a man, a dog, and their ill-fated stroll over the Klondike tundra at -50°F. “You’re stranded in the frigid, freezing wilderness,” the teacher asked the entire class, “and to survive, you’ve got a choice between eating snow and drinking cold running water from a stream. Which do you choose?” Silence. “Running water. Always drink the water. Melting snow into water causes your body to burn extra calories to do it. Water, even freezing cold water, takes less energy for your body to process. In the freezing cold, you’ll survive longer on water than on snow.”...