THE OLD BISHOP'S PALACE IN LINCOLN, England, built in stages between 1155 and the 1880s, was once the splendid residence of medieval clerics. But over the centuries it fell into such disrepair that at one point hares were breeding in the dining room. Now somewhat restored, it is a favorite haunt of Graham Borradaile, a geophysicist at Lakehead University in Thunder Bay, Ontario. The palace has become an integral part of his research. Its old stone walls and towers have enabled him to develop a new technique that will allow archeologists to date precisely stone monuments and buildings whose ages, until now, have been difficult or impossible to determine.