Diagram, 'Section through duplex pendulum seismograph' by J A [James Alfred] Ewing A diagram, labelled figure 1, showing a vertical cross-section of the duplex pendulum seismograph used by Ewing in his investigations into the vibration of the Tay Bridge during the passing of railway trains. Subject: Seismology A diagram based on this photograph was published in volume 44 of the Proceedings of the Royal Society alongside the paper 'Seismometric measurements of the vibration of the new Tay Bridge during the passing of railway trains'. 1888