When President George W. Bush and members of the Senate Judiciary Committee describe John Roberts Jr. as the nominee to be the 17th chief justice of the United States, Ross Davies just chuckles. That isn't a comment on Roberts or his qualifications. What amuses Davies, a law professor at George Mason University, is the number everyone uses. Davies is quite sure that Roberts, if confirmed, will be the 18th chief justice, not the 17th. In a 76-page law review article, set to be published next spring, Davies makes a forceful argument that William Cushing, a mostly forgotten associate justice appointed...