We must now see what happens at the exchange when a call is made. Each operator has control of a number of pairs of flexible cords terminating in plugs, the two cords of each pair being electrically connected. The plugs rest on a shelf in front of the operator, and the cords pass through the shelf and hang down below it. If a plug is lifted, the cord comes up through the shelf, and it is drawn back again by a weight when the plug is not in use. Two lamps are provided for each pair of cords, one being fixed close to each cord. The two wires leading from each subscriber’s instrument are connected to a little tube-shaped switch called a “jack,” and each jack has a lamp of its own. When a subscriber lifts his telephone from its rest a lamp glows, and the operator inserts one plug of a pair into the jack thus indicated, and the lamp goes out automatically. She then switches on her telephone to the caller and asks for the number of the subscriber to whom he wishes to speak; and as soon as she gets this she inserts the other plug of the pair into the jack belonging to this number. By a simple movement she then rings up the required person by switching on the current to his telephone bell. Here comes in the use of the two lamps connected with the cords. As long as the subscribers’ telephones are on their rests the lamps are lighted, but as soon as they are lifted off the lamps go out. The caller’s telephone is of course off its rest, and so the lamp connected with the first cord is not lit; but until the subscriber rung up lifts his instrument to answer the call, the lamp of the second cord remains lit, having first lighted up when the plug was inserted in the jack of his number. When the second lamp goes out the operator knows that the call has been responded to, and that the two subscribers are in communication with each other. Having finished their conversation, both subscribers replace their instruments on the rests, whereupon both lamps light up, informing the operator that she may disconnect by pulling out the plugs.