368 THE ADDRESSES, LECTURES, ETC., OF 



looked for in this direction. The dynamo-machine presents the 

 great advantage of simplicity over steam or other power-trans- 

 mitting engines ; it has but one working part, namely, a shaft 

 which, revolving in a pair of bearings, carries a coil or coils of 

 wire admitting of perfect balancing. Frictional resistance is thus 

 reduced to an absolute minimum, and no allowance has to be made 

 for loss by condensation, or badly fitting pistons, stuffing-boxes, 

 or valves, or for the jerking action due to oscillating weights. The 

 materials composing the machine, namely, soft iron and copper 

 wire, undergo no deterioration or change by continuous working, 

 and the depreciation of value is therefore a minimum, except where 

 currents of exceptionally high potential are used, which appear to 

 render the copper wire brittle. 



The essential points to be attended to in the conception of the 

 dynamo-machine, are the prevention of induced currents in the 

 iron, and the placing of the wire in such position as to make the 

 whole of it effective for the production of outward current. These 

 principles, which have been clearly established by the labours of 

 comparatively few workers in applied science, admit of being 

 carried out in an almost infinite variety of constructive forms, for 

 each of which may be claimed some real or imaginary merits 

 regarding questions of convenience or cost of production. 



For many years after the principles involved in the construction 

 of dynamo-machines had been made known, little general interest 

 was manifested in their favour, and few were the forms of con- 

 struction offered for public use. The essential feature involved in 

 the dynamo-machine, the Siemens armature (1856), the Pacinotti 

 ring (1861), and the self-exciting principle (1867), were published 

 by their authors for the pure scientific interest attached to them, 

 without being made subject matter of letters patent, which circum- 

 stance appears to have had the contrary effect of what might have 

 been expected, in that it has retarded the introduction of this class 

 of electrical machine, because no person or firm had a sufficient 

 commercial interest to undertake the large expenditure which must 

 necessarily be incurred in reducing a first conception into a 

 practical shape. Great credit is due to Monsieur Gramme for 

 taking the initiative in the practical introduction of dynamo- 

 machines embodying those principles ; but when, five years ago, 

 I ventured to predict for the dynamo -electric current a great 





