The bubble is a generally a small amount of a salt solution. The rate is
current dependent.

pete@petertodd.ca wrote:

> > > http://www.surplussales.com/Meters/MtrTime.html
> > >
> > > I'm curious, do they still make them? How do they work anyway?
> > >
> >
> > I'd be surprised if anyone makes them anymore, ROHS compliance would
> > be an issue.
>
> Probably very true.
>
> > They work by electroplating the mercury across the bubble. You feed
> > them a small constant current.
>
> Ahh, so basically the current transports the murcury ions from one
> surface of the bubble to the other? Hence why you can put one in
> reverse, and the bubble goes backwards?
>
> So what's the bubble actually made out of?


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