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A freeper said something about Mercury fuses, and I just did a web search... Found this interesting page:

http://isuisse.ifrance.com/emmaf/terhand/4_2.html

Interesting website located in FRANCE (Gee thanks France!)...http://isuisse.ifrance.com/emmaf/indterhand.html...

Mercury Switches

Mercury switches are a switch that uses the fact that mercury metal conducts electricity, as do all metals, but mercury metal is a liquid at room temperatures. A typical mercury switch is a sealed glass tube with two electrodes and a bead of mercury metal. It is sealed because of mercury's nasty habit of giving off brain-damaging vapors. The diagram below may help to explain a mercury switch.

______________
A / \ B
_____wire +______/___________ \
\ ( Hg ) | /
\ _(_Hg_)__|___/
|
|
wire - |
|
|

When the drop of mercury ("Hg" is mercury's atomic symbol) touches both contacts, current flows through the switch. If this particular switch was in its present position, A---B, current would be flowing, since the mercury can touch both contacts in the horizontal position.

If, however, it was in the | position, the drop of mercury would only touch the + contact on the A side. Current, then couldn't flow, since mercury does not reach both contacts when the switch is in the vertical position.

This type of switch is ideal to place by a door. If it were placed in the path of a swinging door in the verticle position, the motion of the door would knock the switch down, if it was held to the ground by a piece if tape. This would tilt the switch into the verticle position, causing the mercury to touch both contacts, allowing current to flow through the mercury, and to the igniter or squib in an explosive device. Imagine opening a door and having it slammed in your face by an explosion.

Mecury switchs are quite common. The most common place they have been used is in home heating thermostats. If you have a good quality thermostat in your home then pull off the cover and have a look. You will see the glass bulb and ball of mercury that shorts the terminals inside to start your furnace. The tilting of this switch is done by a coil of spring metal that is sensitive to temperature. I also remember seeing these used in security devices and even as a switch to sense when the washing machine lid was open so that the machine would not engage the spin cycle with the lid open.

more HERE

This is datelined: The New Yorker

The Talk of the Town

December 13, 1999, p. 44

Although Iraq remains under a strict United Nations embargo, the embargo does not cover medical supplies. Last year, the Iraqi government ordered half a dozen lithotripters, which are state-of-the-art machines for getting rid of kidney stones. (The word "lithotripter" comes from the Greek for "stone breaker.") A lithotripter uses a shock wave to pulverize these painful objects without surgery. Machines like the ones Iraq bought require a high-precision electronic switch that triggers a powerful burst of electricity. In addition to the lithotripters, Iraq wanted to buy a hundred and twenty extra switches. That is at least a hundred more than the machines would ever need