Pass a little ether through the mercury in the tube, and as soon as
it reaches the empty space it will boil violently, depressing the
mercury, until the pressure of its own vapor is sufficient to prevent
its ebullition. If you now cool the upper part of the tube, so as to
condense the vapor, the pressure being thus removed, the ether will
again begin to boil, and so alternately, as often as you please. In
order to show this fact with effect, the bore of the tube should not be
less than half an inch in diameter.