_Arrange_ as shown in Fig. 80, which is a top view. The wires from C R are connected to the binding-posts of A G at the back, the spring connectors being slipped into them (§ 229). =252. Construction of the Astatic Galvanoscope.= When not to be used for a long time, or for shipping, the legs, A (Fig. 77) may be removed, and the whole packed inside of the box, B. The _Coil_, C, has a resistance of about 5 ohms, and is fastened to the coil-support, C S. The ends of the coil are permanently fastened to the binding-posts, L and R (left and right). The ends are so arranged that when the current enters at L it will pass around the coil in a clockwise direction. =253. The Astatic Needle= (Exp. 106) is supported by a small thread, T, which is tied to the thread-wire, T W. This T W springs into an eyelet, E, which, in turn, rests in a hole made in the end of B. E should turn easily in the hole, but it should not wabble. Fig. 78 shows a sectional view of the coil and needle. The wire, W, should be bent, as shown, so that the magnets can be as near the center-line of C as possible. Fig. 79 shows a front view of the needle. As a matter of convenience it will be best to arrange the poles of the needles, as shown, to agree with the descriptions of the experiments. To keep the needle from being affected by air currents, the glass plate (No. 38) may be placed in front of the box, B. Stand it upon the legs, A, and tie a string around it, and B, to hold it in place. [Illustration: Fig. 78.] [Illustration: Fig. 79.] =254. Adjusting the Needle.= As T is tied to T W, the needle may be swung completely around by turning T W. This should be done until the length of the needle is parallel to the turns of C. The up and down position of the needle should be fixed as nearly as possible when fastening T to T W, the exact place being finally fixed by raising or lowering T W through E. The spring in T W should hold it firmly in E after adjustment. The wire, W, joining the needle-magnets should not touch the coil. It may be made to just swing free from C by tilting the box forward or backward a little. The construction of the legs, etc., makes it possible to tilt the box, and to make it stand firmly upon an irregular surface. [Illustration: Fig. 80.] =255. Directions.= (A) See that there are no magnets within 3 feet of A G. Test the astatic needle, after you have it properly suspended, to convince yourself that it does not try to swing around in a N and S line. In case the needle-magnets have been in contact with other magnets, or are not equally magnetized, remagnetize them as directed in Exp. 106. They must remain in any position given them by turning T W. Finally, bring them parallel to the turns of the coil. (See § 254.) Arrange as in Fig. 80.