/•■/,,,■ J 



^IMMMMII^ 



Figure 76. — Details of the Siemens and Halske dynamo of 1876. For clarity, 

 the brushes have been omitted in the drawing. From R. W. H. P. Higgs 

 and J. R. Brittle, "Some Recent Improvements in Dynamo-Electric 

 Apparatus," Minutes of the Proceedings oj the Institution of Civil Engineers, 1878, 

 vol. 52, pp. 36-98, pi. I. 



of the Gramme dynamos is quite close to that of the 

 Siemens dynamo as measured by Hopkinson and 

 others. 



Up to this point, three-quarters of the way through 

 the 19th century, the electric light was possible, 

 but it was not very practical commercially. Serrin's 

 regulator could be used but it was so delicate that 

 adjustment was difficult, and it was both mechanically 

 and electrically complicated. Only one arc lamp 

 could be used as a load in the circuit of the generators 

 then in use; to place two regulators in the same 

 circuit would, in effect, prevent either one from 

 working. Moreover, the arc light was too bright 



for any purpose other than illuminating large areas, 

 some means had to be found of "subdividing" it so 

 that the brilliancy of a single arc lamp in a single 

 circuit could be spread over many lamps of weaker 

 intensity in the same circuit. Practical electrical 

 generators had been invented, but the initial expense 

 of plant installation — which was that of a gas or steam 

 engine plus the electrical generator and the other 

 electrical equipment that could only be used for a 

 single light — was prohibitive for ordinary purposes 

 (figs. 78, 79). Some means had to be found whereby 

 such a large capital investment could be used for a 

 number of lights that would be of lesser intensity than 



392 



BULLETIN 228 : CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



