. Bulletin. Science. Figure 49.—Siemens' magneto generator, using his shuttle armature. The armature coil {HH) was wound upon the armature core {FGF'). From E. W. Siemens, "Ueber eine neue Construction magnetoelektrischer Ma- schinen," Annakn der Physik, 1857, vol. loi, fig. 2. the cylinder long with respect to the diameter. Another modification was that, instead of the single coil of wire as in the Siemens armature, there were now 16 coils that had their terminals reversed twice each revolution. The 2-part commutator of Siemens was accordingly replaced by a 16-part one. The coils we
. Bulletin. Science. Figure 49.—Siemens' magneto generator, using his shuttle armature. The armature coil {HH) was wound upon the armature core {FGF'). From E. W. Siemens, "Ueber eine neue Construction magnetoelektrischer Ma- schinen," Annakn der Physik, 1857, vol. loi, fig. 2. the cylinder long with respect to the diameter. Another modification was that, instead of the single coil of wire as in the Siemens armature, there were now 16 coils that had their terminals reversed twice each revolution. The 2-part commutator of Siemens was accordingly replaced by a 16-part one. The coils were interconnected at the commutator bars so as to form a single closed-circuit coil.'* Nevertheless, heating of the armature was a con- siderable problem in the original design of '8 British patent 2006 (June 5, 1873); French patent 99828 Quly 5, 1873; addition, June 21, 1878); Engineering, 1873, vol. 16, p. 490; Higgs and Brittle, op. cit. (footnote 72); James Dredge, Electric IHuminalion, London, 1882, vol. 1, pp. 275-293. Figure 50.—Ring armature devised by F^Iias in the 1840's. It was designed for a motor rather than for a generator. From La Lumiere electrique, 1882, vol. 7, p. 14. fig. 13. In order to avoid this, Von Hefner-Alteneck fixed the soft iron core of the armature and rotated the coils. Siemens tried to reduce the temperature by water cooling and by laminating the armature, but the former method was too awkward to be practical, and the latter one was unsuccessful at the time. Very few drum armature dynamos were made and sold; however, the 1876 exhibition in South Kensing- ton showed that these originally unpromising gener- ators had been reduced to practice. The tests of Tyndall and Douglass proved them to be the most efficient of all the units they compared. The armature no longer overheated as it had in the earlier stages of its development, and its output was more constant. In addition, provision was made to reduce sparking at the commutator by
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