Hopkinson, John

(1849-1898), electrical engineer

by T. H. Beare, rev. S. Hong

© Oxford University Press 2004 All rights reserved

Hopkinson, John (1849-1898), electrical engineer, was born on 27 July 1849 in Manchester, the eldest of the five children of John Hopkinson, mechanical engineer, and his wife, Alice, daughter of John Dewhurst of Skipton. Sir Alfred Hopkinson, lawyer, was his younger brother. He was educated under C. Willmore at Queenwood School, Hampshire. In 1865 he became a student at Owens College, Manchester. There he studied mathematics under Thomas Barker and, acting on his advice, entered for and won a minor scholarship at Trinity College, Cambridge, in 1867. At Cambridge he devoted himself to mathematics as his chief study, under E. J. Routh, and in 1871 he graduated from Cambridge as senior wrangler and first Smith's prizeman. While in residence at Cambridge he gained a Whitworth scholarship and proceeded to a degree in science in the University of London (1871). Shortly after his tripos he was elected a fellow of Trinity. In 1873 he married Evelyn Oldenbourg; they had six children.

In 1871 Hopkinson entered his father's works, and in 1872 he became manager and engineer in the lighthouse and optical department of Chance Brothers of Birmingham. In 1872 he first proposed the group flash system to enable mariners to distinguish one light from another. The flashes in his system were of varying length and were separated by varying intervals of darkness which characterized the lights more distinctly. His great mathematical abilities proved to be of the utmost value to him in his optical work, and later on in his electrical work. In one of his papers he proved mathematically that alternating current dynamos could be connected to work in parallel. His views on the relation of mathematics to engineering were fully explained in his James Forrest lecture delivered at the Institution of Civil Engineers in 1894 (PICE, 118, 1894, 530).

Stimulated by the publication of James Clerk Maxwell's Electricity and Magnetism in 1873, and on the advice of Sir William Thomson (Lord Kelvin), Hopkinson later performed a valuable series of experiments on the residual charge of the Leyden jar, and on the electrostatic capacity of glass in 1876-7. The results of these experiments were published in four papers in the Philosophical Transactions of the Royal Society (1876-81), in which he supplemented and improved Maxwell's theory of residual charge. He worked continuously on this subject almost up to the time of his death, and the last paper he published on this question was 'On the capacity and residual charge of dielectrics as affected by temperature and time' (PTRS, 189, 1897, 109-35).

In 1878 Hopkinson resigned his post with Chance Brothers and set up as a consulting engineer in London. In the same year he was elected a fellow of the Royal Society, on whose council he served in 1886-7 and 1891-3. He continued to act as scientific adviser to Chances and was also frequently engaged as an expert witness in patent litigation.

The Paris Exhibition of 1881 brought into prominence electric lighting and electric transmission of power, and Hopkinson served as one of the judges to evaluate different electric lighting systems. Two important papers of his were read before the Institution of Mechanical Engineers in 1879 and 1880. In these he tried to clarify the theory of the dynamo machine and introduced for the first time the notion of the characteristic curve ('On electric lighting', Proceedings of the Institution of Mechanical Engineers, 1879, 1880). In 1882 he obtained his well-known patent for the three-wire system of distributing electricity. In 1883, in an address delivered before the Institution of Civil Engineers entitled 'Some points in electric lighting', he described his first important improvements in the dynamo. The general solution of the problem involved was fully given in a joint paper by Hopkinson and his brother, Edward Hopkinson, in 1886 ('Dynamo electric machinery', PTRS, 1886). The first portion of this paper was devoted to the construction of the characteristic curve for a machine of given dimensions. The second half described the actual experiments conducted on a dynamo to verify the theories set forth in the first, and investigated the causes of discrepancies. This paper was undoubtedly the most important publication by Hopkinson on the practical applications of electricity, and laid the foundation of the accurate design of dynamos through the combination of mathematics and laboratory experiments with engineering skills.

In 1890 Hopkinson was appointed professor of electrical engineering and head of the Siemens Laboratory at King's College, London. Although he did not give lectures while in this position, it gave him the necessary facilities to conduct research on the dynamo. His direction of the laboratory was extremely valuable in stimulating the students and providing advanced students with suggestions for research. In this work he was assisted by E. Wilson, and a number of papers were published in the Philosophical Transactions of the Royal Society between 1894 and 1896 on their joint experiments on the effect of armature reaction, on the efficiency of transformers, and on alternating currents.

In 1885 Hopkinson published the results of a series of experiments on the magnetic properties of iron, for which he was awarded in 1890 a Royal Society medal. Between 1881 and 1883 he worked as scientific adviser to the British Edison Company. During this time he made a significant improvement on the design of Edison's early dynamo. In 1891 he was appointed by the Manchester corporation to advise on the electric lighting of the city, and he acted as consulting engineer while the work was carried out. From 1896 he also worked as consulting engineer to the corporations of Leeds, Liverpool, and St Helens to supervise their works for electric traction. In connection with the Manchester scheme he introduced an important innovation into the system of charging customers for the current used--a system which he had advocated as early as 1883. Under this system the customer had to pay 'a charge, which is calculated partly by the quantity of energy contained in the supply and partly by a yearly or other rental, depending upon the maximum strength of the current to be supplied' (Hopkinson, Original Papers, 1901, 1.254-68).

In the field of electric traction Hopkinson did much professional work. He was consulting engineer to the contractors for the electrical work on the City and South London Railway and in 1896 he was electrical engineer for the Kirkstall and Roundhay tramway at Leeds. He joined the Institution of Civil Engineers in 1877, and in 1895 became a member of its council. He was also a member of the Institution of Electrical Engineers, and was president in 1890 and 1896. It was owing to his initiative that the volunteer corps of electrical engineers (which sent a strong detachment for active service in South Africa in 1900) was formed, and he was appointed the first major in command of this corps.

Hopkinson was an ardent mountaineer and his holidays were usually spent climbing in Switzerland, especially in the neighbourhood of Arolla. His death, at the early age of forty-nine, was due to a terrible alpine accident. On 27 August 1898, he, his son John, and two of his daughters, died while ascending the Petite Dent de Veisivi in the Val d'Herens, an offshoot from the Rhone valley. A few days later all the bodies were recovered; they were buried in the cemetery at Territet. Hopkinson was commemorated at Cambridge by a wing of the engineering laboratory built by his widow and surviving children, including the mechanical and aeronautical engineer Bertram Hopkinson, and at Owens College by an electrotechnical laboratory built by his father and other relatives.

Hopkinson was a man of most unusual achievements. His great powers as an experimenter in the most difficult fields of scientific research were combined with a wide practical knowledge, and in many of his papers he was able in a unique way to employ his high mathematical ability in the solution of practical problems of commercial importance.

T. H. BEARE, rev. S. HONG

B. Hopkinson, 'Memoir', in Original papers of John Hopkinson, 1 (1901), x-lxi
J. Greig, John Hopkinson: electrical engineer (1970)
B. Bowers, 'Edison and early electrical engineering in Britain', History of Technology, 13 (1991), 168-80
The Electrician (10 Jan 1890), 236-7
J. A. E., PRS, 64 (1898-9), xvii-xxiv
CGPLA Eng. & Wales (1898)

Inst. EE, corresp.
RS |  CUL, letters to Sir George Stokes

T. B. Kennington, oils, 1900 (after photographs and portrait, c.1894), U. Cam., department of engineering
W. H. Thornycroft, marble bust, 1902, U. Cam., department of engineering
R. H. Campbell, oils, 1929, Inst. EE
R. H. Campbell, oils, Athenaeum, London
photograph, repro. in Hopkinson, 'Memoir' [see illus.]

Wealth at death  
£74,672 5s. 4d.: probate, 1 Oct 1898, CGPLA Eng. & Wales

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