. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . s is shown in Fig. 4 orFig. 5, the e. m. f. will fluctuate fromzero to its maximum value during eachhalf revolution as shown in Fig. 6. If instead of only a single coil and a Iwo-parl CMnimutator, however, addi-tional coils are placed on the armaturecore, so that when one set of coils is atthe position of no e. ni. f. the other willhe at the position of maximum e. m. f.,as ill the armature shown in Fig, -, thefluctuations will be greatly reduced asshown in Fig, 8. By adding still morecoils an
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . s is shown in Fig. 4 orFig. 5, the e. m. f. will fluctuate fromzero to its maximum value during eachhalf revolution as shown in Fig. 6. If instead of only a single coil and a Iwo-parl CMnimutator, however, addi-tional coils are placed on the armaturecore, so that when one set of coils is atthe position of no e. ni. f. the other willhe at the position of maximum e. m. f.,as ill the armature shown in Fig, -, thefluctuations will be greatly reduced asshown in Fig, 8. By adding still morecoils and coiiinnitator bars, the fluctua-tions in the e. m. f. at the bruslies canbe practically eliminated. An armature of the form shown inFig. 7 is ciUod a ring armature on ac-count of the form of the core. Thesame elTect can be secured with a cylin-drical core by winding each of the fourcoils on the outside of the cylinder andconnecting them together and to thecommutator in the same way as an armature is sliown in Fig. 9and is called a drum armature. Thering type of armature is frequently. FIG. 5. SINGLL GcilL KL\G .\RM.\TURE. used in explaining the theory of dy-namos and motors on account of thegreater ease with which the connec-tions may be followed. In actual ma-chines the drum type is practically al-ways used. If a wire carrying an electric currentis coiled around a piece of iron, the ironimmediately becomes a magnet and re-mains so as long as the current is pass-ing through the coil. Such a deviceis called an electro-magnet. Thestrength of an electro-magnet dependson the number of turns of wire aroundit multiplied by the current in ampereswhich is flowing, that is, on the ampere-turns. Thus, if two electro-magnetsare exactly alike except that one ofthem has four turns of wire carrying acurrent of ten amperes, or forty am-pere-turns, and the other has twentyturns carrying a current of one ampere,or twenty ampere-turns, then the strength of tlie first should be twic
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectrailroa, bookyear1901
