Clovis Chitwood Heavy Industries

I really wanted to bust it open and play with the mercury. I refrained. I bet there’s not enough to really have fun with anyway. Not like the switches in those old style thermostats. I always wanted to stick them in my guitars so that the would automatically switch off when they went vertical. Maybe if I ever upgrade my thermostat I’ll savage the one in there. I wonder if you can still buy them? The old school thermostats or the mercury switches. Ever look at one of those old thermostats. They are pretty clever. They use a spring to measure the temperature. As it gets hotter the spring expands. That’s what made is so complicated to make an accurate spring powered clock. Temperature changes would cause the spring rate to change and the clock would go faster or slower (or was it the rate changed as the spring unwound?). The solution was to make a main spring of two different types of metal that had different rates of expansion. That way the differences would cancel each other out. Those guys were clever. What made the spring the bane of chronometerers makes it perfect for thermostats. You just position the mercury switch, oh yeah I never explained what a mercury switch is did I. A mercury switch is a glass tube with a wire embedded on each end. It is partially filled with mercury which is conductive. When the switch is vertical the mercury collects at the bottom of the switch and there is no connection. As you tilt the switch towards the horizontal at some point the mercury comes into contact with both wires and completes the circuit. So you just stick the mercury switch on the spring so that when it expands the switch goes from on and off. If you look in the thermostat you will see how adjusting the temperature control moves the switch around on the spring. The cool bit is if you watch the thermostat with the cover off and the lights out if you move the temperature control at the point the mercury makes contact with both wires there is a blue flash through the little tube. Of course those new fancy computerized thermostats still can’t switch automatically from heat to cool and you can’t amuse yourself in the dark with them. So much for progress.