It is spheroidal in shape as is noted for the fact of its very seldom burning out, i. e., the electricity heating the wires of the armature to such an extent as to destroy the insulation or fuse the wires, either rendering the armature useless. It is made by keying two dish-shaped iron disks SS Fig. 12, to the shaft x and putting ribs dd about ten in number in the twenty-five light machine, and over the whole putting varnished paper. Then at stated intervals, pegs JJJ are driven into suitable holes in the disks and ribs to help in winding wire on the shell. Next three insulated wires of equal length are joined together at h Fig. 13, and the three wires are then wound over the shell in the following peculiar manner: one half of No. 1 is wound so as to form a zone of a sphere of which the shaft is in the same plane as the center circumference of the zone. The armature is then turned on the shaft as an axis 120° and one half of No. 2 is wound in the same manner as the first half of No. 1. The armature is moved 120° more and all of No. 3 is wound. The armature is then turned back, 120° on the shaft as an axis and the remainder of No. 2 is wound. Lastly the armature is turned back 120° more and the rest of No. 1 is wound. They are bound by wires gg Fig. 13 to hold them when rotating. The object of this rather complicated winding is to get the three coils equi distant from the shaft in order that each coil will generate practically the same current. Now as will be seen the overlapping wires will form a nearly spherical armature. The armature is mounted on the shaft x as an axis which extends far enough out from its bearings to put a pulley on the end H and a commutator on the other end to the three parts of which are fastened the three wires marked one, two, three, Fig. 13.

It has been urged that the repairs of this armature will be larger than on any other armature. If there should be a “burnout” it would necessitate the taking apart of the dynamo and sending the armature to the factory to be rewound. But it never burns out except through positive carelessness and it will be found that the repairs on this armature is less than on the armatures of its several powerful rivals taken separately even though they be of simpler construction.

When the Thomson-Houston armature is rotated between the cup-shaped fieldmagnets alternate currents are generated in each coil in turn and now the next point to be considered is the