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TELEGRAPH KEY. Make this from the last wood block and a metal strip 4” by l/2”. Bend the strip as shown. Use round-head screws for the terminals. Now you can connect all the parts to see the relay in action.      A MESSAGE COMES IN. Note that when the low-voltage telegraph key is depressed (from miles away, remember?), the nail becomes an electromagnet and pulls the strip down. This closes the higher-voltage circuit, lighting the bulb. When the key is released, the electromagnetic field collapses, the strip springs upward, and the bulb circuit opens.