DYNAMO-ELECTRIC MACHINES. 87 



totally different arrangement of field magnets. European makers 

 have endeavored to have as little dead weight in motion to absorb 

 the energy of the motor as possible, whilst Edison seems to have 

 gone to the other extreme, and increased the dead weight of the 

 moving parts beyond everything that is necessary. Both Siemens 

 and Gramme have constructed machines for 250 lamps of 20 candle 

 power, far lighter than those of Edison. The Gordon dynamo will 

 light 8600 lamps of twenty candle power, and weighs eighteen tons. 

 This will give a lighting capacity of about 5 00 lamps, or 1 000 half lamps, 

 of ten candle power per ton. The Edison machines built here for 

 500 half lamps of 7 candle power, weigh about four tons each, which 

 would only be an average of 125 lamps per ton of 7 candle power as 

 compared with the Gordon of 1000 half lamps of ten candle power 

 per ton. A difference of 8 to 1 in favor of the Gordon machine, 

 with regard to the number of lamps, and of eleven and six-tenths to 

 one per ton in lighting power. 



The greatest novelty, however, in dynamos, is one that has just 

 been tried in England, called the Ferranti-Thompson Machine, the 

 joint invention of an Italian, Mr. S. Ziani de Ferranti, and Sir Wm. 

 Thompson, who is so well known in the world of electrical science. 

 This machine weighs only 1200 lbs., and at its trial in London, 

 recently, lighted 320 Swan lamps, of 20 candle power, with an inten- 

 sity of light equal to 15 or 17 candles actually. The number of half 

 lamps per ton to this machine would be 1060. The most remarkable 

 feature about this remarkable machine is its armature, which, inde- 

 pendent of the shaft and pulley which drive it, weighs only 18 lbs. 

 The armature alone of the Edison 500 half lamp machine, weighs in 

 the neighborhood of 1000 lbs , which would give a weight of two lbs. 

 per lamp, as compared with the weight of one lb. to seventeen five 

 tenth lamps, of the Feranti-Thompson, or as 35 to one in favor of 

 the latter. Its armature is totally different in construction from any- 

 thing that has been made, being a single strip of copper half an inch 

 wide, one twelfth of an inch thick, and 1020 ft. long. It is wound 

 as if on a gear-tooth-shaped wheel, and has another wheel with inter- 

 nal teeth pressed over it, so that its shape around its periphery is like 

 a toothed wheel. Each turn of the coil is insulated from the other 

 by a layer of tape. 



Having thus given a faint outline of the history of dynamo machines, 



