<p>Historians are often in the business of telling us how badly our myths fall short of reality, so it's a rare treat when a writer comes along to tell us that reality is far grander than we had imagined. That's what Brandeis historian David Hackett Fischer has done in "Washington's Crossing" (Oxford, 564 pages, $35), a meticulous and brilliantly colored account of the period surrounding George Washington's famous sally across the Delaware River in 1776. The tale is told in the style of a master thriller writer who keeps us reading even though we know -- or think we know -- how it all turns out.</p>