Editor’snote: This is a reprint (slightly edited) of a paper of the same title that appeared in the bookPhysicsandOurWorld:ASymposiuminHonorofVictorF.Weisskopf, published by the American Institute of Physics (1976). The personal tone of the original talk has been preserved in the paper, which was itself a slightly edited transcript of a tape. The figures reproduce transparencies used in the talk. The demonstration involved a tall rectangular transparent vessel of corn syrup, projected by an overhead projector turned on its side. Some essential hand waving could not be reproduced.