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Computers and computing; from the beginning.
Recent
For most of human history the passage of time has been measured by the Sun, and the distance you could walk in a day. Now all of humanity is synchronized to the vibrations of the same Cesium atoms.
Local Time Until very recently telling the time meant how much daylight was left in the sky from where you were standing. Since Biblical times the “hour of the day” meant which fraction (usually 1/12th) of the daylight had expired. The first hour was sun up, the last hour was sundown. An “hour” was not a fixed duration of time, but varied throughout the seasons.
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The first commercial use of electricity was not lighting, but communicating over wires. And it was done with nothing more than batteries, switches and coils.
The word telegraph means writing from a distance and the term was first used in France in the 1790’s to describe an optical network called the Chappe Telegraph. This system used special flags with moveable arms that were placed at the top of towers, six miles apart, and could encode various letters and numbers based on the positions of the arms. Residents of the towers used special telescopes to observe the signals from other towers. This system was so successful that at it’s peak, in 1846, there were over 522 towers covering over 3000 miles across France, Belgium and part of Italy. Messages could be sent from Paris to Northern Italy in about 30 minutes. That’s a 13 hour train ride today, or eight days on foot.
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Voltage is what makes electrons flow, and when they flow in one direction we call it direct current.
People have found it helpful to think of electricity as a fluid that flows along a wire. Voltage is like a pressure, pushing that fluid along. We now know it’s not a fluid, but when it flows we still call it a current. When this current flows through a wire a pretty astounding thing happens. It immediately forms a magnetic field around the wire. Magnetism is as mysterious as electricity; it shouldn’t surprise us that the two are so intertwined, but there you have it.
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