The torsion-pendulum analyser was described in 1936 before a joint meeting of the Section of Seismology of the American Geophysical Union and the Eastern Section of the Selsmological Society of America. The purpose of the machine is to compute mechanically the motion of simple oscillators when known accelerations are applied to their supports. More specifically, its purpose is to compute the motion of a pendulum when accelerations, which are obtained from an accelerograph-record during an earthquake, are applied to its support. The same method can be used to compute the motion of a building or other engineering structure. In practice this is done manually by slowing up all of the motions 100 or 200 times. The earthquake-effects are thus reproduced in slow motion.