At the front a similar strip is made and attached. This latter has a small hole in the middle of it to serve as a bearing for the forward end of the shaft. Across the top of the motor a brass strip or band is made fast with machine-screws; and at the angles formed by the front ends of the side-strips and the front cross-strips hard-wood blocks are attached. To these the brushes and binding-posts are made fast, so that one brush at the top of the left-hand block rests on the top of the commutator. The one at the underside of the opposite block must rest on the underside of the commutator. [Illustration: FIG. 44] [Illustration: FIG. 45] The armature core is made up of laminations as described for the dynamo armatures. In a really efficient motor the armature should have eight or more channels. The other parts of the motor may be assembled and wired as described on the preceding pages. The armature should be wound with No. 20 or 22 insulated copper wire, and the field with No. 16 or 18. For high voltage, however, the armature should be wound with finer wire and a rheostat used to start it. A Third Type of Motor The third type is but a duplicate of the series-wound dynamo, the general plan of which is shown in Fig. 40. This motor can be made any size, but as its dimensions are increased the weight of the field-magnets and armature must be proportionately enlarged. For an efficient and powerful motor, the field should stand ten inches high and six inches broad. The iron cores are five inches long and one inch and a half in diameter. These should be made by a blacksmith and bolted together. The armature is three inches in diameter and four inches long, and should develop two-thirds of a horse-power when sufficient current is running through the coils to drive it at sixteen hundred revolutions. The wiring is carried out as shown in Fig. 40, and the armature hung and wound as suggested for the dynamo shown in Fig. 28, page 246. Chapter XI GALVANISM AND ELECTRO-PLATING Simple Electro-plating To the average boy experimenter, electro-plating is one of the most fascinating of the uses to which electricity may be put. In scientific language the process is known as electrolysis, and involves the separation of a chemical compound into its constituent parts or elements by the action of an electric current and the proper apparatus. Electrolysis cannot take place, however, unless the liquid in the tank, commonly called the electrolyte (no relation to electric light), is a conductor.