{ Effect: Bell rings from central but does 13. Open magneto Armature { not ring when magneto handle is turned Winding. { nor can central be called. { Test: Ring with another magneto or test { set. 14. Slight Short Circuit { Effect: Can ring operator but cannot hear (escape) to { nor be heard clearly. Ground. { Test: Open line, one line at a time, and { follow circuit with test set. Escapes are { due to wires touching damp walls, metal { roof, or other grounded wire where { insulation has been rubbed off. Signaling by Means of Lamps. Visual signaling by means of the lamp has been found to be very important and efficient. Experience has shown that during the first hours of a battle, particularly in an advance, before it has been possible to establish the telephone systems, the lamp has furnished the most dependable means of communication both by day and night. Even in stationary or trench warfare in sectors with well organized systems of communication, the lamp is most serviceable in transmitting short messages such as calling for a barrage, reinforcements, etc., for which arbitrary signals are used. In fact, this method is more precise than the use of rockets and more rapid than the telephone in transmitting information covered by these arbitrary signals. For these reasons, all important telephone lines near the front are paralleled by the lamp system.