The capacity of the transformer is approximately 100 watts. The dimensions and details of construction described and illustrated are those of a transformer intended for use upon a lighting current of 110 volts and 60-cycles frequency. The frequency of most alternating current systems is 25, 60, or 120 cycles. The most common frequency is 60. Dimensions and particulars of transformers for 25 and 120 cycles will be found in the form of a table farther on. The frequency of your light circuit may be ascertained by inquiring of the company supplying the power. [Illustration: Fig. 181.—The Core, Assembled and Taped.] The first part to be considered in the construction of a transformer is the core. The core is made up of thin sheet-iron strips of the dimensions shown in Figure 180. The iron may be secured from almost any hardware store or plumbing shop by ordering "stove-pipe iron." Have the iron cut into strips 1 1/4 inches wide and 24 inches long. Then, using a pair of tinner’s shears, cut the long strips into pieces 3 inches and 4 3/4 inches long until you have enough to make a pile of each 2 1/2 inches high when they are stacked up neatly and compressed. The long strips are used to form the "legs" of the core, and the short ones the "yokes." [Illustration: Fig. 182.—Transformer Leg.] The strips are assembled according to the diagram shown in Figure 180. The alternate ends overlap and form a hollow rectangle 4 1/4 x 6 inches. The core should be pressed tightly together and the legs bound with three or four layers of insulating tape preparatory to winding on the primary. After the legs are bound, the yoke pieces may be pulled out, leaving the legs intact. Four fiber heads, 2 1/2 inches square and 1/8 of an inch thick, are made as shown in Figure 183. A square hole 1 1/4 x 1 1/4 inches is cut in the center. Two of these are placed on each of the assembled legs as shown in Figure 184. [Illustration: Fig. 183.—Fiber Head.] The primary winding consists of one thousand turns of No. 20 B. & S. gauge single-cotton-covered magnet wire. Five hundred turns are wound on each leg of the transformer. The wire should be wound on very smoothly and evenly with a layer of shellacked paper between each layer of wire. The two legs should be connected in series. The terminals are protected and insulated by covering with some insulating tape rolled up in the form of a tube. The secondary winding consists of one hundred turns of No. 10 B. & S. gauge double-cotton-covered wire. Fifty turns are wound on each leg, over the primary, several layers of paper being placed between the two. [Illustration: Fig. 184.—Leg with Heads in Position for Winding.] A "tap" is brought out at every ten turns. The taps are made by soldering a narrow strip of sheet-copper to the wire at proper intervals. Care must be taken to insulate each joint and tap with a small strip of insulating tape so that there is no danger of a short circuit being formed between adjacent turns.