From the 1916 catalogue of the L. E. Knott Apparatus Co. of Boston: "Improved Sabine's Torsion Pendulum for determining the moment of torsion of a wire and the moment of inertia of a ring. Two methods of reading torsional vibrations are possible, -- by direct observation of consecutive transits of the index past the zero point of the graduated arc; by observing through a telescope the consecutive clashes from the illuminated mirror. The disc is 10½ inches in diameter, and is clamped to the wire by means of a small chuck fixed at its middle point. This disc is then supported from the frame by a similar chuck having the additional features of an adjusting thumb screw and a set-screw. The index dial is cast from metal and has large raised figures. A ring [whose] moment of inertia is to be determined has the same diameter and mass as the disk... $15.60"
Sabine is almost certainly Wallace Clement Sabine (1868-1919), the Harvard physicist who is best known for his studies of reverberation.