Right. So you... you think of, well what can I... how can I tell if something is true? And the usual way is to think of better reasons. And at some point you say, well I’ll roll the ball down the hill and see if it... see if it reaches a maximum speed or if it keeps going faster and faster. And of course, you’ll get the wrong answer. It’ll reach a maximum speed, but that's... but for the first minute it’s accelerating and you’d get Newton’s law. After a while, it’s going 80mph and never gets any faster because the air's and... I once was looking at an exhibit in the science museum downtown. And one of the features of the science museum is that it has... it has this tube that's very long, about four or five stories. It’s a glass tube about this big. And they drop a feather and a... stone; I forget what the other thing is. And of course, the stone comes down very quickly, or it's a ball... something. And then, the feather slowly drifts, and then they pump the air out of it and do it again and they both come down at the same time, but if you look very closely after they both come down, then you see little pieces of feathers still coming down very slowly. 'Cause there’s still some air in the thing.