CONTINUOUS-CURRENT DYNAMOS. 



PART I. 



ALTHOUGH it is the alternate-current dynamo which 

 of late years has shown the most rapid growth both 

 in theory and use, yet its closely allied partner, the continu- 

 ous-current machine, has not been without steady progress, 

 especially in the field of practice ; it may therefore be of 

 interest to shortly review its recent history, and thence 

 endeavour to forecast the direction towards which future 

 advances will tend. 



The earliest dynamo which was invented belonged to 

 the so-called " uni-polar " or "non-polar" class in which 

 there is no reversal of the direction of the E. M.F. generated in 

 the active wires or " inductors" of the armature. In spite, 

 however, of its invention so far back as 183 1, the uni-polar 

 type finds to this day little or no practical use. Visions of 

 a perfect dynamo, in which a truly continuous current is 

 produced and collected without any reversal of its direction, 

 and therefore without any likelihood of sparking at the 

 brushes, have frequently been revived, and the idea has 

 always presented great attractions. Yet often as the cry 

 has arisen for such a dynamo without a commutator and free 

 from all the troubles incidental thereto, it has never assumed 

 any very practicable shape, the difficulty of generating any 

 considerable voltage within reasonable limits ol size 

 having proved an insuperable obstacle to the ingenuity of 

 inventors. 1 The electrical engineer is thus thrown back on 

 the bi- or multi-polar dynamo with its two principal methods 

 of winding the armature, which are identified with the names 

 of Gramme and Siemens. The theory of the dynamo was 

 in the main worked out from the scientific study and prac- 

 tical use of these machines between the years 1870 and 

 1885 ; but with the date 1886 we reach a most important 

 stage in its history. In the Philosophical Transactions oj the 

 Royal Society io\: that year was published the classic paper of 



1 For a recent examination of several different types of uni-polar 

 machine, see Elcktrotechnische Zeitschrift, nth Aug., 1893. 



