  Tilt switch from old thermostat.
I replaced an old thermostat at our square house in Urbana, Illinois in late 2001, and this is the tilt switch from it. It had probably been there for decades. A thermostat works by mounting this kind of tilt switch on a coiled bi-metallic strip, which coils and uncoils slightly as the temperature changes. When the switch tilts out of level the mercury flows to one side or the other, turning on the heat or air-conditioning depending on the direction of tilt. The weight of the mercury tips the balance slightly further in the direction it went, providing a built-in hysteresis effect.
Reports Kathy Tattersall from Wolfram Research, Inc:I just clicked on Mercury and saw the switch you used. It brought back fond memories of my Dad who used to invent so many gadgets that are now used in our everyday lives (but he never patented any of them!!) :(
Back in the mid to late 50's he made a mercury switch...it was a glass tube with the mercury in it and it was then connected by a long electrical cord to our TV so when commercials came on he would "tip" the switch and shut off the sound!!! He made one for my grandfather and uncles he even got fancy and made a wood box around the glass tube to protect the tube from breaking and the left over Mercury my brother and I used to play with!! (horrors!!) I loved to watch the mercury split then pull itself back together again!
Source: Hardware Store
Contributor: Theodore Gray
Acquired: 15 April, 2002
Text Updated: 11 August, 2007
Price: $10/new thermostat
Size: 1"
Purity: >95%
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