4500. Imagine a silver thread descends from your aircraft straight down to the ground, and at the end of that thread is a brass plumb bob and its point is not touching the ground but is just one inch above it.
4501. The ground is level, the plum bob, attached to the plane by a string is traveling along the road. Since the plane is going one hundred miles an hour, so also will the plumb bob be going one hundred miles an hour.
4502. The farm with the silver roof comes into the sight of the plumb bob and it roars past, it passes the mailbox and the yew bushes to either side of the mailbox so fast that the letters of the name on the mailbox, and its number cannot be seen, they are just a blur.
4503. So the plum bob goes on its way down the highway still roaring along at a hundred miles an hour, but you, up in your passenger seat in your little plane, see that the barn with the silver roof is going past you as slow as it is possible for a thing to move.