A very interesting photo illustration from the 1903 volume of the Book of Knowledge with fourteen photographs with descriptions on How to Signal Across a Field. The semaphore system was used to convey messages over long distances. This illustration depicts a woman in turn of the century dress showing the use of flags. The top row shows the signal "ready to start"; the second means "the signs that follow are to be read as letters" and the third means "The signs that follow are to be read as numbers. The fourth means "cancel previous signal." Finally, the other pictures convey the message "tea is ready" each picture representing a letter. Just a little more involved than text messaging.