The trouble with them was the cost of the mercury, particularly during war time.
Turing once suggested that "Mercury Line Memory" could be made with Gin... --I've always wanted to try it.
There is some analogy here with bubble memory (though that moved around physical material rather than just set up a wave).
I wonder what the minimum spacing of such waves would be, how this would compare with current estimates on the upper bounds of density for silicon and if material fatigue factors into this somehow. I can't imagine such a system to be very stable mechanically.
I'm really not sure, and I'd rather not speculate blindly. I've read
about the basics of Mercury Line Memory in the past, and have some
books that describe it, but I don't know the hard details.
BTW, Mercury Line Memory was not the first form of memory used in
programmable computers. The "oldest" or "first" is debatable, but
the earliest were switches/relays and vacuum tubes (AFAIK). I'd
bet jgrahamc would know...
I wonder what the minimum spacing of such waves would be, how this would compare with current estimates on the upper bounds of density for silicon and if material fatigue factors into this somehow. I can't imagine such a system to be very stable mechanically.