The modern pattern of “sounder” as used by the British Post Office for reception of telegraphy. Dots and dashes are distinguished by the interval between the sounds of the instrument. It consists only of an electromagnet, with its armature lever arranged to stop against an anvil or screw in such a way as to give a distinct and somewhat loud sound. The magnet is wound to a resistance of 40 ohms (or 900 ohms when worked from accumulators), and the instrument is worked with a current of 400 milliamperes (25 milliamperes with accumulators).