And that's because the air molecules found on the outside, such as oxygen molecules, carbon dioxide molecules, nitrogen molecules, exert a certain force on these two sections here on this liquid. And when the force of these molecules equals the force of the gravity on the liquid, when these two forces equal, it will stop pulling down, and it will level off at some height H. So then you can calculate that height H from this point to this point. And you can use this formula to find the pressure of the atmosphere where pressure is equal to density of liquid times gravitational constant times height H.
So let's see what happens when the atmosphere pressure increases. Suppose you decrease the altitude where you are measuring the pressure, so the pressure increases. If the pressure increases, then the force will increase. That's pushing down this liquid.