In 1869, Zollner described his horizontal pendulum with the suspension which has since been associated with his name. A mirror on the pendulum was used to reflect a light beam from a lamp to a scale, where the motion of the pendulum, as magnified by the optical lever, was directly observed. The instrument was installed in the cellar of the university in Leipzig; Zoller could detect significant movement of the pendulum due to the filling up of the auditorium on the second floor of the building. The pendulum was built in order to observe changes in the direction of gravity due to tidal forces, but Zollner suggested that it might also be valuable as a seismometer.
Horizontal pendulums were to be widely used in seismographs after 1880, because they could be given long periods and could still be compact. There were several different suspensions used in these later horizontal-pendulum instruments. The Zöllner suspension was used in the Galitzin horizontal seismograph.
