Andy's Blog: Cannonball In Mercury: "He's saying Mercury can be short, as in a short column of Mercury in a barometer. Sure, it's 30 inches, give or take (erm 75ish cm), because of its density.
Torricelli's experiment was that you could put a liquid (preferrably a heavy one) in a column that's sealed at the bottom, turn it upside-down, and place it in a further container of mercury as the liquid draws down from the top, a space with a vacuum is created at the top. Doing so struck a blow to the existing thought that nature abhors a vacuum.
I'm not sure if the barometric propeties of Torricelli's apparatus were obvious, but they must've become obvious as people around the world measures different heights of the mercury.
As for Mercury being short and portable, it's true-- you can hold something 30' tall in your hands. To do the same thing with water requires 33 feet, or about 10 meters."