Why doesn't a mercury barometer containing vacuum get crushed by the atomospheric pressure? Here is what I think might be the reason. Although there is vacuum inside a mercury barometer, that vacuum is pressurized by the atmosphere that pushes mercury from the reservoir. That pressure is cancelled out by the pressure exerted by the atmosphere from outside onto the barometer tube containing the vacuum. Did I get it right? Additional question: Suppose I take a test-tube that can contain only 700 mm of mercury. Then, I fill this test-tube up with mercury, and place it in the reservoir. Now, since the atmosphere from outside is putting pressure on the reservoir at 1 atmospheric pressure, should this pressure make the mercury kept in the reservoir try to rise the level of the mercury inside the test-tube, and having failed to do so, expand the volume of the test-tube or break it apart?