[Illustration: Fig. 147.] =EXPERIMENT 188. Motion with two electromagnets.= =451. Directions.= (A) Arrange as in Fig. 147. Join the two coils, H and E, in parallel. Connect their two outside ends O E to a metal plate A, and their inside ends I E to B. Join wires 1 and 6 to K, D C, A and B, as shown. When the circuit is closed at K, the current will pass along wire 1 and divide at A, entering E and H at the same time by wires 2 and 4 and returning through 3 and 5 to B, and thence to D C. (B) Close the circuit for an instant with wires arranged as in Fig. 147. Do the electromagnets attract or repel each other? Study out the direction in which the current passes around the coils, and see whether they _should_ attract or repel. (C) Change wire 4 to B, and wire 5 to A. The polarity of H, only, will be changed when this circuit is closed. Press the key for an instant and study the results. _=452. Discussion of Exps. 183-188.=_ From the results it is evident that motion can be produced with the aid of the electric current in many different ways. It can be produced at the ends of wires which simply reach across the room, or which reach miles from the source of the current. To get practical results for commercial purposes we require a proper source of current, proper conductors, and proper apparatus to convert the motions into useful work. The motions given to the parts of the apparatus in the previous experiments are not suitable for commercial purposes, as they are in straight lines. A rotary motion is needed to do good work; and when this is applied to a shaft, belts can be used to run all sorts of machinery. (See Electric Motors.) [Illustration: Fig. 148.] =EXPERIMENT 189. Rotary motion with a hollow coil of wire and a permanent magnet.= =453. Directions.= (A) Arrange as in Fig. 148. A key can be used instead of the reverser. The coil of the galvanoscope, G V, has a magnetic field about it when the circuit is closed. The needle has a permanent field. (B) Close the circuit for an instant, let the needle swing back past the zero mark, close the circuit again, etc., until the added impulses give the needle a complete turn. (C) Keep the needle turning on its axis by opening and closing the circuit at the proper time. With a little practice you can make it turn rapidly. (D) Reverse the motion of the needle. (See § 455.) [Illustration: Fig. 149.] =EXPERIMENT 190. Rotary motion with an electromagnet and a permanent magnet.=