原文 / 英語
コピー
There is the heliograph, that device used by the U.S.Navy to catch and reflect the sun's rays into the eyes of men miles away and spell out a message to them. Then there are thousands of ear-signals. The whistle of a policeman or referee, the siren of an ambulance or fire engine, the bell at your door or in the classroom, all convey messages as clearly as though they were spoken.