engineer in London, and in the same year he was elected a fellow of the Royal Society, serving on the council 1886-7 and 1891-3. He continued to act as scientific adviser to Messrs. Chance Brothers, and was also frequently engaged as an expert witness in patent cases.
The Paris exhibition of 1881 brought into great prominence electric lighting and electric transmission of power, and in this exhibition Hopkinson showed an alternate current dynamo of a new type, and a hoist with reversible motor. Two important papers from his pen in 1879 and 1880 were read before the Institution of Mechanical Engineers ; in these papers he endeavoured to elucidate the theory of the dynamo machine, and he introduced for the first time the notion of the characteristic curve (Proc. Inst. Mech. Engineers, 1879-80). In 1882 he took out 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 ' (Inst. of Civil Engineers' lectures on 'The Practical Application of Electricity'),he described his first important improvement sin the dynamo ; but the general solution of the problem involved was not given to the world until the publication of a joint paper by Hopkinson and his brother, Edward Hopkinson, in 1886 (Phil. Trans. 1886). In this paper the first portion was devoted to the construction of the characteristic curve for a machine of given dimensions, and the second half to a description of actual experiments on a dynamo to verify the theories set forth in the first part, and to an investigation into the causes of any discrepancies. This paper was undoubtedly the most important publication by Hopkinson on the practical applications of electricity, and was the foundation of the accurate design of dynamos in accordance with theory.
In 1890 he was appointed professor of electrical engineering and head of the Siemens Laboratory at King's College, London. Though he did no actual teaching in connection with this post, it gave him the necessary facilities for carrying on his researches on the dynamo, and his direction of the laboratory was of great value in stimulating the students, and providing advanced students with suggestions for researches. In this work he was assisted by Mr. E. Wilson and a number of papers were published in the 'Philosophical Transactions of the Royal Society' on their joint experiments on the effect of armature reaction, on the efficiency of transformers, and on alternating currents (Phil. Trans. 1894-6).
In 1885 he published the results of a series of experiments on the magnetic properties of iron, and for his researches in this subject he was awarded in 1890 a Royal Society medal.
It was not until 1891 that Hopkinson had an opportunity of carrying out any constructive engineering of importance outside the field of lighthouse work. In that year he was appointed by the corporation of the city of Manchester as their adviser on the electric lighting of the city, and he acted as consulting engineer during the carrying out of the work ; from 1896 he was also consulting engineer to the corporations of Leeds, Liverpool, and St. Helens, in respect of 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 ; he had advocated this method as far back as 883. In the plan adopted the customer of he electricity supply works 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.'
In the field of electric traction he did a large amount of professional work ; he was consulting engineer to the contractors for the ilectrical work on the City and South London Railway, and in 1896 he was electrical ngineer for the Kirkstall and Roundhay Tramway at Leeds.
He joined the Institution of Civil Engineers in 1877, and in 1895 became a member of the council. He was also a member of the Institution of Electrical Engineers, and twice filled the office of president. 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 mountain climber, and his holidays were usually spent in 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 Aug. 1898, accompanied by his son John and two of his daughters, he began the ascent without guides of the Petite Dent de Veisivi in the Val d'Herens. an offshoot from the Rhone valley ; how the accident, which led to the death of the whole party, occurred will never be known. A few days later the bodies of all were recovered and were buried in the cemetery at Territet. He is commemorated at Cambridge by a wing of the engineering
