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 1873. 



'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, ed.. 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 including an arrangement 

 for shifting the position of the brushes. 



At first the drum armature did not seem as practical 

 as the ring armature, for it was quite difficult to 

 wind the coils on the drum and to insulate the suc- 

 cessive coils from one another; so, the advantage 

 of the many-part commutator of Gramme seemed 

 lost. In addition, ventilation was much easier for 

 the ring than for the drum, particularly when the 

 drum was a solid rather than a hollow cylinder. 



374 



BULLETIN 228: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



