When the thistle funnel is moved upwards towards the surface of the liquid, the height h of the liquid column in the vertical tube will decrease. This is because as the thistle funnel is moved upwards, the pressure at the bottom of the vertical tube (due to the weight of the liquid above it) decreases. According to Pascal's principle, pressure in a fluid is transmitted equally in all directions. Therefore, as the pressure at the bottom of the vertical tube decreases, the height h of the liquid column in the tube also decreases in order to maintain equilibrium of pressure.
