Sometimes a moment can change history. This one took 1/250th of a second.Boston, April 5, 1976. As the city simmered with racial tension over forced school busing, newsman Stanley Forman hurried to City Hall to photograph that day's protest, arriving just in time to snap the image that his editor would title "The Soiling of Old Glory." T he photo made headlines across the United States and won Forman his second Pulitzer Prize. I t shocked Boston, and America: Racial strife had not ended with the 1960s, it was alive and well in the cradle of liberty. Louis P. Masur's evocative "biography of a photograph" unpacks this arresting image in a tour de force of historical writing.