Corresponding to the 32 poles of the field-magnet, each circuit of the armature has 32 copper bars, connected in series by transverse pieces. There arc therefore, in all, 00 (3 X 32) bars on the armature. The three circuits are joined up to each other in at manner similar to the three circuits of the Thomson-llouston arc-untehinv. The armatnre-core is snrrounded by a cast-iron frame, and the whole can be moved along the bed-plate for cleaning and other purposes, leaving the tield-magnet open to view, as shown in Fig. 100.
The exciting circuit is coiled round a sort of east-iron pulley. Two steel rims, each armed with 16 horns forming pole-pieces, are bolted on to the policy. one on either face. in the manner shown in detail in Fig. 110. This arrangement permits of the maximum utilization of the magnetic 1111x, and blith the copper and the exciting current are reduced to a mininunn. The construction of a field-magnet of this type is very simple, the :12_p tic magnet living hi only four Sepnrat e parts --it great advantage in a piece of moving mechanism subject, to henry stresses. The exciting current is taken to the field-magnets by means of two metallic bands, catch of which passes round it grooved ring on the spindle, and round a pulley connected to a (See Pig. 108.) The armature is overhung, the massive spindle being carried on a dou ble bracket bolted to the laid-plate. A machine of this type can work equally well as a synchronizing mobil., but it differs from an ordinary motor, inasmuch as it can be made to start without difficulty.
The total weight of copper on the field-magnet is only :300 kilogrammes. To excite the umehine s11 as to ffiVe 50 volts on open eirenit, only.] 00 watts are required: that is to say, per cent of the output. At full load. owing to the reaction of the armature, this amount is
sli fitly increased, but it never exceeds a fraction of 1 per cent. AI full speed and with normal volts the flirt ion losses amount to :3,6iNi watts, :Moat 1.1i to per cent of the maxi mum output. The ('' I' loss in the armature-conductors at hill load is 3.500 watts. This gives at total efficieney of 96 per emit. The total weight of the machine without bell-plate is ;1,000 kiloaranones.
The virulency of the dynamo is greater thim that of any other converter of energy. The of sue!' nmehilm., made by a committee of the Franklin institute, in connection with the Electrical Exhibition of ItiI8•1, gave the following results; For more complete and detailed descriptions of dynamos, the reader is referred to the fol lowing: Prof. Sylvanus P. Thompson, Dynamo Electric Machinery ; Dredge, Electric ; Esson, Magneto- and Dynamo-Electric Machines ; Schellen, Magneto- and Dynamo Electric Machines; Atkinson, Electric Lighting; Kapp, Electric Transmission of Energy ; Fleming, The Alternate-Current Transformer ; Kapp, Alternate-Current Machinery ; Mordey, Alternate-Current Working, Jour. Inst. Elec. Eng., London, vol. sviii., p. 583, et seq. ; Kapp, Predetermination of the Characteristics of Dynamos, Jour. Soc. Tel. Eng., 1886 ; E. Hop kinson, The General Theory of Dynamo Machines, British Assoc., Manchester meeting, 1887 ; J. Hopkinson, Proc. Roy. Soc., 1885, Part II. See also Trans. of the Am. Inst. of _Elect. _Eng., Jour. Inst. of _Elect. Eng., London ; and to the files of The Elfctrical Engineer, N. Y., Elec trical World, Electrician, Electrical Review, La Lumiere Electrique, and other electrical journals.