THIS DAY IN SCIENCE: Email in the 18th century: The Optical Telegraph in 1791

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A pendulum is constructed from a 1.0-kg mass suspended from the ceiling, with a length of strong string long enough so that, when pulled about 40o from the vertical, the mass comes to nose level. The pendulum will be released from this position. The demonstrator is to remain absolutely still until the pendulum makes at least one full cycle. This very-simple-to-perform demo can be made very memorable by playing up the drama. The possibility of seeing the teacher’s blood will excite the class. It will even test one’s faith in the laws of Physics.

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