Diagram, experimental results by J [John] Hopkinson A graph showing the results of experiments made 'upon a very soft iron wire' during Hopkinson's investigations into electrical resistance of iron at a high temperature. He describes the graph: 'The abscissae are the temperatures as estimated by the resistance of a copper wire, the ordinates represent the resistance of the iron wire having unit resistance at 20 degrees Celsius.' Subject: Electricity / Metallurgy A print of this graph was published in volume 45 of the Proceedings of the Royal Society as 'Electrical resistance of iron at a high temperature'. 1889