. Bulletin. Science. Figure 51.—Pacinotti's ring armature, as used in a motor, with a field produced by electro- magnets. Pacinotti found he could use the machine as a generator by replacing the field electromagnets with permanent magnets. From La Lwniere electrique, 1882, vol. 7, p. 15, fig. 14. But the inherent advantages of the drum armature were greater. After it was discovered that the coils could be inserted in slits on the core and better methods of laminating the core and of winding the coils were introduced, the drum armature was put to use; it has remained in use to the present time.
. Bulletin. Science. Figure 51.—Pacinotti's ring armature, as used in a motor, with a field produced by electro- magnets. Pacinotti found he could use the machine as a generator by replacing the field electromagnets with permanent magnets. From La Lwniere electrique, 1882, vol. 7, p. 15, fig. 14. But the inherent advantages of the drum armature were greater. After it was discovered that the coils could be inserted in slits on the core and better methods of laminating the core and of winding the coils were introduced, the drum armature was put to use; it has remained in use to the present time. But the production of current in all these early generators was hampered considerably by the lack of sufficiently strong fields. Charles Wheatstone had introduced electromagnets into the generator that he used for his telegraph of 1845, but this arrangement was generally deemed too clumsy as it required chemical cells in addition to the generator itself.''^ In 1864, Henry Wilde patented a generator in which a magneto was substituted for the chemical cells (fig. 57). The current from the magneto was then used to excite the electromagnet field coils of another generator. One motor drove both magneto generator and electromagnet generator.*" A few years later William Ladd simplified the double structure by combining the two separate fields in one unit (fig. 58). Wire was wound around permanent bar magnets which were placed parallel to and above each other. An armature was rotated between each pair of poles at the end of the magnets. One armature provided current for the coils on the permanent magnets and so added to the latter's field while the output current was taken from the other armature.*' When demonstrated at the Paris Exhibition of 1867, both Wilde's and Ladd's machines produced '9 British patent 10665 (May 6, 1845). s» British patent 3006 (June 4, 1864); Henry Wilde, "Experi- mental Researches in Magnetism and Electricity," Philosophical Magazine, 1866,
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