通訊(Communication)
when men began to like together in small communities, they it was necessary to find ways of sending messages from one community to another.
even in earliest times there were several different ways this could be done. really rapid communication was not possible until electricity was put to work. in 1844 the first electric telegraph was constructed. thirty years later the telephone was invented. soon a whole succession of inventions was produced: the wireless telegraph and the radio, the motion picture, and television.
earth satellites today bring valuable information almost instantaneously to our homes by means of electrical signals.