If you will look once more at the picture of the key you will see under the long handle (or lever) a little point which the lever will touch when it is pressed down. Now this little point is part of that insulated leg, and, therefore, this point is also insulated from the base. If a current of electricity were sent along the wire it could not get any farther than this point unless we put in some arrangement to complete the path, or circuit, for it to travel in. We therefore put in the switch. One end of the switch (which is made of brass with a rubber handle) is fastened on the base of the key, so that it may be moved to the right or left. The other end, when the switch is moved to the left (or "closed"), touches a piece of brass fastened to the little point we have mentioned, and so makes a free path for the electricity to go through the base of the key and through the wire to the sounder, and from there to the battery, and so back to the earth. This switch must be opened before the sounder near it will respond to its neighboring key. Now we are ready to send a message. Suppose we want to send a telegram from New York to Philadelphia. The operator in New York opens his switch and presses down his key several times. The switch on the Philadelphia key being closed, the electricity goes through to the sounder, and, this being made an electromagnet by the current passing through the wire, the iron armature is attracted by the magnetism and drawn down to the magnet with a snap. It will stay there as long as the New York operator keeps his lever pressed down, but, when he allows it to spring up, there is no current passing through the Philadelphia sounder and there is no magnetism, consequently the armature springs up again with a click. As often as the operator presses down his key lever and lets it spring up again, the same action takes place in the sounder, and it makes that click, click, which you have heard if you have ever seen telegraph instruments in operation. Let us continue, however, to send our message. The New York operator, having pressed down his key several times to signal the Philadelphia operator, closes his switch to receive the answer from Philadelphia. The operator in the latter city then opens his switch and presses down his key several times, which makes the New York sounder click, in the same way, to let the operator there know that he is ready to receive the message. He then closes his switch and receives the telegram which the New York operator sends after opening _his_ key. Telegraphic messages are sent and received in this way and are read by the sound of the clicks.