Philadelphia's judiciary will have royalty on the bench next week.

Retired Supreme Court Justice Sandra Day O'Connor, 78, the first woman named to the high court and its only living former justice, will serve as a visiting judge on the U.S. Court of Appeals for the Third Circuit on Thursday and Friday.

O'Connor is the first former Supreme Court justice to sit on the Third Circuit "to my knowledge," said Chief Judge Anthony J. Scirica, a 20-year veteran.

O'Connor is scheduled to hear oral arguments in four cases, sitting with Judge Marjorie O. Rendell and Scirica. She'll help rule on 12 others based on written briefs.

"Both Midge and I are very excited about this," he said. "It's a great day in the history of the Third Circuit. It will be thrilling to sit with one of the great justices in the history of this country."

Anticipating a crowd, the Third Circuit has assigned both 9:30 a.m. sessions to the Ceremonial Courtroom of the federal courthouse in Center City. It seats 200, more than twice the capacity of the other courtrooms, Scirica said.

Cases on O'Connor's docket involve disability regulations at UPS Inc.; a federal prisoner's habeas corpus petition; whether a person can own a gun in the United States after a conviction in Puerto Rico; and an effort to force the federal Occupational Safety and Health Administration to issue safer limits for worker exposure to known carcinogens.

O'Connor, who has homes in Washington and Phoenix, has heard cases in seven other federal appellate circuits since retiring in January 2006 to care for her husband, who has Alzheimer's disease. She also serves on the board of the National Constitution Center here.

Scirica said he extended the invitation to O'Connor, whom he labels "a friend. I don't claim to be close friends."

O'Connor, nominated to the high court by President Reagan, a Republican, in September 1981, makes such judicial visits fewer than six times a year, said Jeffrey Toobin, author of the acclaimed

The Nine: Inside the Secret World of the Supreme Court

.

"She's still intellectually vigorous," he said. "She likes to keep her hand in. It's a public service, and it's an honor for the circuit judges."

Lewis Powell and Byron White, both deceased, also served as visiting judges after they retired from the Supreme Court, according to Toobin. Chief Justice William Rehnquist died in September 2005.

A moderate centrist, O'Connor "was the most influential justice on the court," in Toobin's view. "As the swing vote, she decided the outcome of case after case."

Because of O'Connor's record on the bench, "I think she was the most influential woman in American history," Toobin said.