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.
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].
(B) Press lever 2 of C R ([§ 235]) for an instant only. This allows the current to enter A G at L. Repeat several times until you thoroughly fix in your mind the direction in which the right-hand end of the needle is deflected. Does the needle jump suddenly when the current passes?