XV111 



been more varied, or more uniformly successful than his. Two of his 

 more considerable works the lights of Macquarie and Tino are 

 described in a paper which he read before the Institution of Civil 

 Engineers, in 1886. 



In 1878 he removed from Birmingham to London to practice as a 

 consulting engineer. But his connection with Messrs. Chance was not 

 broken, and he remained for many years their scientific adviser. 

 Lighthouse design, however, was only one of several fields of work in 

 which the influence of his originality was coming to be strongly felt. 



At the time of Hopkinson's removal to London the dynamo electric 

 machine had just ceased to be regarded as little more than a scientific 

 curiosity. Its application to electric lighting had begun ; the possi- 

 bility of reversing its function and using it as a motor had been 

 pointed out ; but the conditions which should govern its design were 

 very imperfectly understood, and the patterns of machine then manu- 

 factured were crude, clumsy, and wasteful. It is to Hopkinson more 

 than to any other man that the modern dynamo owes its efficiency. 

 His first published work on the subject is to be found in two papers on 

 electric lighting, which were read and discussed before the Institu- 

 tion of Mechanical Engineers in 1879 and 1880. These papers 

 describe experiments made by the author on a Siemens dynamo, to 

 determine the relation of the electrical output to the power expended 

 in driving the machine. The relation of current to potential was 

 exhibited graphically in a form which has since been widely used by 

 electrical engineers under the name of the "Characteristic curve." 

 This pioneer work was followed by a series of magnetic researches 

 which paved the way for a general theory of the magnetic circuit of 

 the dynamo machine published by the brothers John and Edward 

 Hopkinson in the 'Philosophical Transactions ' for 1886. The principles 

 then laid down, were of fundamental importance, and their influence 

 on design was revolutionary. Hopkinson himself was the first to 

 apply them in practice. Taking as the basis of his operations the form 

 of machine designed by Edison, he modified it in accordance with the 

 theory he had demonstrated, and the Edison-Hopkinson dynamo, with 

 its improved armature and greatly shortened magnetic circuit, was 

 speedily accepted not only as a machine of extraordinary merit, but as 

 the embodiment of principles guiding all dynamo design. 



Hopkinson was now in the full swing of his work as an electrical 

 engineer, inventor, and expert. Among other inventions which 

 appear in his numerous patents are the closed circuit trans- 

 former, the three wire system of electric distribution, and the series- 

 parallel system of motor working in electrical railways and tramways. 

 His inventions bear striking evidence of his scientific prescience ; in 

 several instances they w^re made too soon to bring him much or any 

 return. His professional .success however was great. At an unusually 



