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2022-02-15 10:21:55
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long-distance
Bill invented telephone,but four years later,he invented another talking device-- photophone.the photophone used a beam of light travelling through the air.he believed that this invention was very important,but the sun was not constant and it only travelled short miles.as the technology developed,laser \ optical fibra can carry light beam long distances,these developments made his dream came into true.
in early days,when people in danger they put an evenlope into a bottle, and threw it in the sea,in case some fisher man or seaman may found it. know what had happened.
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