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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 
speed, 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 metal near the axis of rotation 
is neutralised, as the dimensions increase, by the excessive 
heat generated by the magnetisation 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 construction 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 
