An apparatus for the precision measurement of the motion of torsion pendulums having glass samples as their elastic elements is described. The temperatures used range from -90° to 1200°F.; the range of frequencies is 0.1 to 10 cycles per second. Both the decay of a simple pendulum and sustained oscillation of a driven pendulum are used. The basic observation used for all measurements is elapsed time, the least increment of which is 10 microseconds with the apparatus used. Examples of the data obtained for The American Ceramic Society standard sample of soda-lime glass and for fused silica are given.