If you and your friends wish to share a secret, you can write it in code (编码), and no one else will be
able to read it.
     Codes are one way of writing in secret. Ciphers (暗码) are another. In a code each word is written as a
secret code word or code number. In a cipher each letter is changed. Codes and ciphers have played an
important role in the history of the world. Julius Caesar, the Roman ruler who defeated almost all the countries
in Europe about 2, 000 years ago, used a cipher when he sent secret messages to his troops. During the
American Revolution, George Washington's spies used a kind of code to send him information about the enemy
before his military (军事的) action. In World War Ⅱ, the Americans "broke", or figured out, Japan's most
important navy codes and got enough information to destroy a powerful Japanese fleet( 舰队).
     Storekeepers use codes to mark their goods. The codes show how much was paid for the goods or when
 they were added to the stock (商品). Businessmen use codes to hide plans from their business enemies.
Sometimes personal letters or diaries are written in code. Many people enjoy figuring out codes and ciphers
simply as a hobby.
     In the 16th century, codes and ciphers were very popular among scientists. They wrote messages to each
other in code so that no one else would learn their secrets. Geronimo Gardano, an Italian astrologer (星相家),
mathematician, and doctor, invented the trellis cipher. He took two sheets of paper and cut exactly the same
holes in each one. Then he sent one sheet, which he called a trellis, to a friend and kept the other for himself.
Whenever he wanted to write a message, he put his trellis over a clean sheet of paper and wrote the secret
message through the holes. Then he removed the trellis and filled the rest of the paper with words that would
make sense. When his friend received it, he put his trellis over the writing and read the secret message.