the world > the earth > weather and the atmosphere > weather > study or science of weather > meteorological instruments > [noun] > barometer > height of mercury in > (proportional) rise and fall > fall (2)
The sinking down or contraction of the fluid in a barometer or thermometer (said also of the instrument itself); = fall, n.2 14b.
spec. The sinking down or contraction of the fluid in a barometer, thermometer, or similar measuring instrument. Said also of the instrument itself.