Diagrams, experimental equipment and results by J B Peace Eight diagrams, labelled figures I-VIII. Figures I and V show schematic diagrams of the experimental setup used by Peace in his investigations into the potential difference required to produce a spark between two parallel plates in air at different pressures. The remaining diagrams are graphs showing the results observed by Peace relating to potential difference, electrostatic force and pressure. Subject: Physics / Electricity Prints of these diagrams were published in volume 52 of the Proceedings of the Royal Society alongside the paper 'On the potential difference required to produce a spark between two parallel plates in air at different pressures'. 1892