Alang wrote:
wrote:
A mercury switch has a curved or bent glass tube with 'contacts'
typically at the middle and one end, and obviously containing a bit of
mercury. As it's tilted the mercury bridges the contacts to complete
the circuit.

The one have in the shed is a straight glass tube with contacts at one
end. The tube has to be tilted to at least 30 deg from horizontal to
let the contacts be bridged. In actual use they were set to flip up to
a vertical position.

I've seen them. What I've never seen is an open one - all the ones I've
seen have been a *sealed* tube.

Andy