. The science-history of the universe . ake upby degrees, and reach their maximum in less time thanit takes to read this paragraph. One other radical improvement in dynamo-electric ma-chines remains to be recorded, namely, that due to theFrench inventor Gramme. The essence of this lay in thestructure of the armature. While previous to Gramme allarmatures had been constructed either like spools of cottonor like balls of yarn wound on blocks, he made his arma-ture by starting with an iron ring (itself consisting of acoil of soft iron wire), and winding the copper wire onthis by passing the end o
. The science-history of the universe . ake upby degrees, and reach their maximum in less time thanit takes to read this paragraph. One other radical improvement in dynamo-electric ma-chines remains to be recorded, namely, that due to theFrench inventor Gramme. The essence of this lay in thestructure of the armature. While previous to Gramme allarmatures had been constructed either like spools of cottonor like balls of yarn wound on blocks, he made his arma-ture by starting with an iron ring (itself consisting of acoil of soft iron wire), and winding the copper wire onthis by passing the end of the wire again and againthrough the ring. A Gramme armature ring, cut and bent 196 ELECTRICITY out partly, and with some of its copper coils removed, isshown in Fig. 15. The cut ends of the iron wires con-stituting the ring-core are shown at A, and B shows a por-tion of the copper-wire coils wound around this copper wire is continuous throughout as regards itselectric connection, but at frequent intervals a loop of this. Section of a Gramme Ring Armature. wire is carried out and attached to a segment of the com-mutator. This armature being rotated in a magnetic field—,between the poles of powerful field magnets—tends todeliver a substantially continuous current to brushestouching the commutator segments at points midway be-tween the poles of the field magnets. It will be remem-bered that the iron ring constituting the core of the ELECTRO-MAGNETIC MACHINERY 197 Gramme armature was made of iron wires, and not of asolid piece or ring of iron. The object of this was to pre-vent the formation of electric currents in this ring-coreitself, commonly called Foucault currents, which would bea cause of inconvenience by heating the armature and ofloss by wasting energy in the useless production of thisheat. The Siemens armature had no such provision, andaccordingly very serious difficulties were experienced inthe running of machines using such armatures by reasonof
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