I have a question about a particular phenomenon that I've noticed for some time. When light comes in through the window and projects onto the floor. It seems like I can see the air moving upward when there is a heater in the room. It seems like the upward movement of the air is somehow visible on the floor, but when I look at the air with my eyes, I can't see any movement. Is there some reason for this? I was thinking that maybe our eyes don't focus on a particular part of the air, so we don't see the movement, but maybe the light on the floor is a projection of one particular spot, and so you can see the air moving? I hope this is understandable.