Editing Mercury switch (section)

==Description==
Mercury switches have one or more sets of [[electrical contact]]s in a sealed [[glass]] envelope that contains a small quantity of mercury. The envelope may also contain hydrogen at pressure, an [[inert gas]], or a vacuum. Gravity constantly pulls the drop of mercury to the lowest point in the envelope. When the switch is tilted in the appropriate direction, the mercury touches a set of contacts, thus completing an electrical circuit. Tilting the switch in the opposite direction moves the mercury away from that set of contacts, breaking that circuit.<ref>{{cite book |first=Jacob |last=Fraden |title=Handbook of Modern Sensors - Physics, Designs and Applications |edition=3 |publisher=Springer - Verlag |year=2004 |pages= 256–257 }}</ref> The switch may contain multiple sets of contacts, closing different sets at different angles, allowing, for example, single-pole, double-throw (''[[Changeover switch|SPDT]]'') operation.