From three-quarter-inch round iron cut two cores, each three inches and a half long, and thread them at both ends, as shown at B B in Fig. 17. From band-iron five-eighths of an inch thick and one inch and a half wide cut a yoke (A), and bore the indicated holes two inches and three-quarters apart, centre to centre. These should be threaded so that the cores (B B) will screw into them. From a bar of iron cut off two blocks one inch and a half by one inch and a half by two inches for the lugs. Now, with a hack-saw and a half-round file, cut out one side of each lug, as shown at C. These lugs are to be bored and threaded at one end, so that they can be screwed on the lower ends of the cores (C C). For a larger dynamo the yoke should be made six inches long, one inch thick, and two inches and a half wide. The cores should be of one-inch iron pipe. These will be hollow, as shown at B B in Fig. 18. For the ends cast-iron blocks must be made or cast from a pattern two inches and three-quarters square and four inches high, as shown at C. The yoke (A) and the lugs (C) are bored and threaded to receive the one-inch pipe, and when set up this will constitute an iron field-magnet six inches wide, two inches thick, and nine inches high. This, if properly wound, should develop a quarter of a horse-power. [Illustration: FIG. 17] [Illustration: FIG. 18] [Illustration: FIG. 19] [Illustration: FIG. 20] [Illustration: FIG. 21] The parts shown in Fig. 17, when screwed together, will give you a field-magnet two by one and a half by five and three-quarter inches high, and will appear as shown in Fig. 19, A being the yoke at the top, B B the cores, C C the lugs, and D a strip of brass screwed fast across the back of the lugs (C C), and in which a hole is bored to act as a bearing for one end of the armature shaft. Between the lugs and the strip (D) fibre washers three-eighths of an inch in thickness are placed to keep the strip away from the lugs. A hole is bored directly through the middle of each lug, from front to rear, and it is threaded at each end so that a machine-screw will fit in it. The brass strip (D) is five-eighths of an inch wide, three-sixteenths of an inch thick, and four inches long. Copper or German-silver may be used in place of brass, but iron or steel must not be employed, since these metals are susceptible to magnetism. Two holes should be made in the bottom of each lug, and threaded, so that machine-screws may be passed through a wooden base and into them in order to hold the dynamo on the base.