We then prepare a base (J) of any hard wood, 2 inches thick, 8 inches long and 8 inches wide, and bore two 3/4-inch holes 3 inches apart on a middle line, to receive a pair of 3/4-inch cap screws (K), which pass upwardly through the holes in the base and screw into the pole pieces (C). A wooden bar (L), 1-1/2" × 1-1/2", 8 inches long, is placed under each pole piece, which is also provided with holes for the cap screws (K). The lower side of the base (J) should be countersunk, as at M, so the head of the nut will not project. The fields of the dynamo are now secured in position to the base. [Illustration: _Fig. 24._ DETAILS OF THE ARMATURE, CORE _Fig. 25._ DETAILS OF THE ARMATURE, BODY] THE ARMATURE.--A bar of iron (Fig. 24), 1" × 1" and 2-1/4 inches long, is next provided. Through this bar (1) are then bored two 5/16-inch holes 1-3/4 inches apart, and on the opposite sides of this bar are two half-rounded plates of iron (3) (Fig. 25). ARMATURE WINDING.--Each plate is 1/2 inch thick, 1-3/4 inches wide and 4 inches long, each plate having holes (4) to coincide with the holes (2) of the bar (1), so that when the two plates are applied to opposite sides of the bar, and riveted together, a cylindrical member is formed, with two channels running longitudinally, and transversely at the ends; and in these channels the insulated wires are wound from end to end around the central block (1). MOUNTING THE ARMATURE.--It is now necessary to provide a means for revolving this armature. To this end a brass disc (5, Fig. 26) is made, 2 inches in diameter, 1/8 inch thick. Centrally, at one side, is a projecting stem (6) of round brass, which projects out 2 inches, and the outer end is turned down, as at 7, to form a small bearing surface. [Illustration: _Fig. 26._ JOURNALS _Fig. 27._ COMMUTATOR, ARMATURE MOUNTINGS] The other end of the armature has a similar disc (8), with a central stem (9), 1-1/2 inches long, turned down to 1/4-inch diameter up to within 1/4 inch of the disc (7), so as to form a shoulder. THE COMMUTATOR.--In Fig. 27 is shown, at 10, a wooden cylinder, 1 inch long and 1-1/4 inches in diameter, with a hole (11) bored through axially, so that it will fit tightly on the stem (6) of the disc (5). On this wooden cylinder is driven a brass or copper tube (12), which has holes (13) opposite each other. Screws are used to hold the tube to the wooden cylinder, and after they are properly secured together, the tube (12) is cut by a saw, as at 14, so as to form two independent tubular surfaces. [Illustration: _Fig. 28._ END VIEW ARMATURE, MOUNTED] These tubular sections are called the commutator plates. [Illustration: _Fig. 29._ TOP VIEW OF ARMATURE ON BASE]