All the deductions which have hitherto been made require to be supplemented in a way which M. Faraday first indicated. It was he who enriched our knowledge of electricity by a whole series of new facts; with an almost prophetic insight he suspected them, afterwards subjecting them to experimental confirmation. His achievements have placed him in the front rank of experimental physicists for all time. When his experimental ability was greatest he was engaged, during the years 1837—1839, in studying some problems of electrostatics: these dealt with the phenomena of electrostatic induction which one have already mentioned, the effect of the medium on the phenomena of electrostatic repulsion and attraction, which they discuss and other problems covering a much wider range. The forces of attraction and repulsion are influenced to a very great extent by the nature of the medium; for all substances he found that the forces were less than when air was the medium.