The University of Glasgow's Blackstone Chair.
Scotland's oldest five universities all made use of a "black stone" in the ritual of student examinations, and there are surviving references to one at the University of Glasgow from 1647. In 1775 the marble cutter Archibald Shaw was commissioned to saw and polish a "black stone" for the University, and it was incorporated in a new mahogany chair. An hourglass was suspended within a laurel leaf fixed upon the upper rim of the back.
During an examination, the student sat on the marble seat of the chair and answered questions on his subject for as long as sand flowed in the glass above his head (and out of his sight!). This method of oral examination ended in 1858 with the introduction of written examinations.
Reference: Glasgow University Archive Services, OD 16252
University of Glasgow
Blackstone Chair, chairs, furniture, hourglasses, mahogany, marble, marble cutters, student examinations, students, University of Glasgow