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early age he attained an almost unique position as an engineering con- 

 sultant, mainly but by no means wholly in electrical matters. His 

 frequent appearances in the law courts as expert witness represented 

 only one side of a busy arid varied professional life. In recent years 

 his engineering work has concerned itself much with electric traction 

 as well as with the carrying out of large schemes of electric lighting, 

 He was engineer of the Manchester electric supply, and of electrical 

 tramways at Leeds and Liverpool. He took part, as a member of 

 Council, in the management of the three great engineering societies 

 the Institutions of Civil, Mechanical, and Electrical Engineers. The 

 Electrical Engineers twice made him their President (in 1890 and 

 1896). His presidential address in 1890 was devoted to a review of 

 results of magnetic research, remarkable, as indeed all his papers were, 

 for its lucid brevity and comprehensiveness. In his address in 1896 

 he proposed the formation of a volunteer corps of electrical engineers. 

 The corps was formed and he was himself its first Commanding 

 Officer. 



Throughout this active professional life, Hopkinson made time for 

 a remarkable amount of purely scientific work, much of which was of 

 first-rate importance. His published papers began to appear as early 

 as 1871. They number in all about sixty-five. Ten of them are to 

 be found in the ' Philosophical Transactions,' and many more in the ' Pro- 

 ceedings ' of the Society.* About half of the whole number deal with 

 magnetism, and with the applications of electricity and magnetism in 

 engineering. It was in this field that Hopkinson accomplished the 

 part of his work that is most widely known. Before these subjects 

 engaged his attention, however, he had broken other ground which he 

 continued to cultivate at intervals for many years. His earliest papers 

 refer to miscellaneous problems in elasticity to the rupture of an iron 

 wire by a blow, and to the stresses produced in a disc by rapid rota- 

 tion. His connection with Chance's works led him to investigate the 

 refractive indices of glass, and this led on through the connection 

 afforded by Maxwell's theory of light to a prolonged research dealing 

 with electrostatic capacity and the phenomena of residual charge. Two 

 papers on the residual charge of a Leyden jar were published in the 

 ' Transactions' in 1876 and 1877 and were followed by others on the 

 electrostatic capacity of glass and liquids,! and on specific inductive 

 capacity,^ and by a final paper " On the Capacity and Eesidual Charge 

 of Dielectrics as affected by Temperature and Time." It is impossible, 

 in a few sentences, to give any adequate summary of this important 



* It is satisfactory to know that a collected edition of Hopkinson's papers will 

 be published by the Cambridge University Press. 

 f ' Transactions,' 1877 and 1880. 

 J ' Proceedings,' 1886 and 1887. 

 ' Transactions,' 1897. 



