One end of the field winding is connected to one of the brushes. The other brush and the other end of the field form the terminals to which the battery is connected. The motor, being of the two-pole armature type, must be started when the current is turned on by giving it a twist with the fingers. *A Larger Motor* may be built in somewhat the same manner as the one just described by cutting armature and field out of sheet tin. It will be more substantial if it is built up out of laminations and not bent into shape, as in the case of the other. Lay out an armature disk and a field lamination on a sheet of tin in accordance with the dimensions and pattern shown in Figure 249. These pieces are used as patterns for laying out the rest of the laminations. [Illustration: Fig. 250.—Complete Motor.] Place them on some thin sheet-iron and trace the outline with a sharp-pointed needle. Then cut a sufficient number of pieces of each pattern to form a pile three-quarters of an inch thick. Four laminations for the field should be cut with extensions shown by the dotted lines. They are bent out at right angles for mounting the motor and holding it upright. Assemble the armature and field by piling the pieces on top of each other and truing them up. Enough laminations should be used to form a pile three-quarters of an inch thick when piled up and clamped tightly. File off any burrs and rough edges and then bind the laminations together with some string to hold them until wound. Wrap a couple of layers of paper around those portions of the armature and field which are liable to come into contact with the iron. Five or six layers of No. 18 B. & S. gauge double-cotton-covered magnet wire are sufficient to form the field coil. The armature is wound with three or four layers of wire of the same size. The commutator is made out of a circular piece of hard wood or fiber, fitted with segments cut out of thin sheet-copper. The segments may be fastened to the core with thick shellac or some melted sealing-wax. The ends may be bound down tightly by wrapping with silk thread. The brushes are cut out of thin sheet-copper similar to that used for the commutator segments. The bearings are strips of heavy sheet-brass bent into the shape shown. They are mounted by passing a nail through the holes in the ends and through the holes, A and B, in the field and then riveting the ends over. Assemble the motor as shown in Figure 255. If desirable, a small pulley may be fitted to the shaft and the motor used to run small mechanical toys. If it is properly constructed, two or three dry cells will furnish sufficient current to run the motor at high speed. CHAPTER XVII DYNAMOS There is perhaps no other electrical device entering into the young experimenter’s domain requiring the careful workmanship and tool facilities that the dynamo does. In order to construct a practical working dynamo it would be necessary to have at hand a lathe for turning the castings.