Diagrams, experimental equipment and results by W H [William Henry] Preece Four graphs of EMF, current and specific gravity and a diagram of the porcelain supports used by Preece to avoid 'electrical leakage' during the course of his investigations into charging secondary batteries. This diagram shows two cups filled with resin oil resting on the supports. Each of the five diagrams has a corresponding engraved print. Subject: Electricity The prints were published in volume 38 of the Proceedings of the Royal Society alongside the paper 'On charging secondary batteries'. 1885