Here's some vocabulary you may need to understand the passage on the next page:
cipher - noun: A note written in a secret code.
telegraph - noun: A device used to send a message at a distance over a wire (usually in Morse code).
message - noun: A note to a person, usually brief and written.
key - noun: Something important for explaining.
variation - noun: Something changed a little bit.
cryptography - noun: The act of writing in code or cipher.