rewebster said:
didn't Einstein write a paper on this?
If so, I'm unaware of it, and wonder what his interest
would have been in the topic. It seems like something
that would be very straightforwardly explained by classical
hydraulics / gas law theories long before Einstein's time.
I know that fluid filled manometers were often used for
measuring pressures from atmospheric all the way down
to moderately high vacuum levels in lab settings,
and it wouldn't be uncommon to leave one connected
to one's vacuum system even once the pressure had
gone down to the point where the manometer wouldn't
be able to usefully measure it (p < 1 Torr).
Of course you'd need to use good vacuum pump oil or
mercury or something vacuum compatible in the tubes.