Strange Electrical switches

Hi, I bought my home in 1976. For some ungodly reason, the light switches
were retrofit with these small, flat, half-oval switches. They are connected
to a central 15 volt(?) transformer in a closet; when you push one of these
switches down, you can hear a slight buzzing noise a few feet above it,
where a relay turns on the A.C. Someone told me that these are "mercury"
switches, but I cannot validate this. This is a MAJOR pain in the butt for
me, as it will not allow me to put a dimmer anywhere in the house, but the
REAL problem is that I cannot find these things ANYWHERE, and no electrician
seems to know anything about them. They are starting to break, and I am
getting nervous. Any insight that you might be able to part with here?
Thanks, C