In fact, one is impossible without the other.

Air, though you can neither see it, nor grasp it, nor weigh it, is just as solid as granite when it comes to filling or emptying a room.

Not a foot, not an inch of it can be forced into a room anywhere, until a corresponding foot or inch is let out of it somewhere.
Therefore, never open a window at the bottom until you have opened it at the top.

If you do, the cold fresh air will pour in onto the floor, while the hot foul air will rise and bank up against the ceiling in a layer that gets thicker and thicker, and comes further and further down, until you may be actually sitting with your head and shoulders in a layer of warm foul air, and your body and feet in a pool of cool pure air.

Then you will wonder why your head is so hot, and your feet so cold! Currents and Circulation of Air.