Smart doorbells
While teaching at the Albany Academy, Mathematics and Natural Philosophy professor Joseph Henry dabbled in a little physics and happened to discover self-inducting currents. Thus followed a period of experimentation with electromagnets, and somewhere around 1831 he found a novel way to apply this newfound knowledge: by stringing a mile of wire around a classroom, attaching a bell to one end and an actuator to the other. The bell rang: he had invented the electric doorbell as we know it. Sure, the doorbell was one of Henry’s least notable inventions (his work on the electrical relay basically gave life to the telegraph, creating modern communication as we know it) but it was so incredibly sound that its fundamentals barely changed for nearly two centuries.
Even today, many of us have an electrically activated bell next to the front door. The doorbell is technology so simple that
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