The liquid runs out of the submerged open end of the tube and into the dish until the level in the tube falls to 76 centimeters. Like a see-saw in balance, the barometer balances the when the weight of the liquid in the tube exerts the same pressure as the air outside. Thursday Hold a plastic bag of water and you can feel its weight. But hold the bag while you're submerged in the swimming pool and you won't notice the weight anymore. It's sort of the same with air- air has weight, but we don't notice it because we've become acclimated to the pressure it exerts.
Air presses in all directions.
To demonstrate this, fill a glass to the brim with water. Place a square of cardboard on top of the glass, making sure it makes a strong seal. Now, holding the cardboard in place with one hand, carefully turn the glass upside down. Anyway, if you carefully release the cardboard . . . Air is pressing up on the cardboard with enough force to hold the water in the glass.