133 



contrived by Dr. Werner Siemens, of Berlin. While 

 possessing several advantages, in point of efficiency over 

 that of Saxton, the Siemens armature requires to be driven 

 at a high velocity to produce a succession of currents suffi- 

 ciently rapid to be available as a substitute for the voltaic 

 battery. Little inconvenience however arises from the high 

 speed when the armatures are of small dimensions, but as 

 the dimensions increase it becomes necessary to lower the 

 speedj and the large machines are, consequently, not pro- 

 portionately powerful with the smaller ones. Besides this, 

 the advantages possessed by this form of armature in 

 having the moving mass of met?J near the axis of rotation 

 is neutralised, as the dimensions increase, by the excessive 

 heat generated by the magnetisa^tion and demagnetisation 

 of the iron ; it would also be convenient in some circum- 

 stances to drive a machine direct from the crank or fly- 

 wheel of a steam-engine, without the intervention of multi- 

 plying gearing. 



Considerations of this nature led the author, towards the 

 end of 1866, to propose to himself the constniction of an 

 electro-magnetic machine with multiple armatures, which 

 should remove the inconveniences inherent in those hitherto 

 constructed, by producing a greater number of currents for 

 one revolution of the armature axis. Since that time he 

 has been engaged, with more or less interruption, in carry- 

 ing out this design, and has at length constructed a machine 

 the performance of which surpasses all his previous essays 

 in this direction, in regard to power and efficiency, and 

 with a considerable reduction in the quantity of the mate- 

 rials employed. 



The machine in which these results are embodied consists 

 of a circular framing of cast iron^ firmly fixed together by 

 an iron bridge and stay rods. A heavy disk of cast iron is 

 mounted on a driving shaft, running in bearings fitted to 

 each side of the framing. One of these bearings is carefully 



