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Light switch
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===Mercury switch=== <!--"Mercury (element)" links here.--> [[File:mercurylightswitch.jpg|thumb|upright|Mercury light switch from General Electric {{Circa|1960}}, 120Β V 15Β A]] Around the middle of the 20th century, "quiet" switches were introduced that used mercury to make the connection, avoiding the loud snap made by the spring-loaded toggle switches that were then the norm. One form of mercury light switch uses a sealed glass vial that is tipped by the toggle lever, causing a drop of liquid metallic [[mercury (element)|mercury]] to roll from one end to the other, bridging a pair of contacts to complete the circuit. Another style of mercury light switch uses a metal wheel with an insulator separating the two halves that has a hole which allows the mercury to connect either side of the wheel in only one position.<ref>{{cite patent | country = US | number = 2101115 | status = patent | title = Electric switch of the fluid flow type | pubdate = 1937-12-07 | gdate = 1937-12-07 | fdate = 1935-10-29 | pridate = 1935-10-29 | inventor = Warren R Walker | invent1 = Walker | assign1 = General Electric Vapor Lamp Co }}</ref> Some of these switches were also equipped with a [[neon lamp]] connected across the contacts, and thus in series with the electrical load. This caused the indicator to glow faintly when the switch was off, as an aid to finding the switch in a dark room. By the 1970s, other quiet switch designs that did not require mercury (and were thus simpler and cheaper to produce) came into widespread use, gradually replacing both conventional "snap" toggle switches and mercury-based quiet switches. {{Clear}}
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