How do changes in atmospheric pressure affect the height of the column of mercury in a barometer?
Well, we know that
And thus a mercury column, a mercury barometer, is an excellent means to monitor atmospheric pressure, or pressures LOWER than atmospheric pressure. Mind you, mercury has all but disappeared from laboratories and doctors' surgeries in that (i) it is toxic; and (ii) if you spill the mercury it is very difficult to clean it up.
And the length of the column is proportional to the pressure exerted on the column, i.e.
Of course, daily variations in atmospheric pressure will cause the length of the column to vary. Would the length of the column be the same at altitude? Why or why not?