Professor Duhem supported his case by citation of Greek, Byzantine, and Arabic sources and by use of writings of fourteenth century physicists available only in manuscripts. But unfortunately for his main contention he overlooked a remarkable passage written by Adelard of Bath over a century before Roger Bacon. In the fifty-eighth chapter of the _Natural Questions_ the nephew says, “There is still one point about the natures of waters which is unclear to me.” He then asks his uncle to explain a water jar, similar to that just described, which they had once seen at the house of an enchantress. Adelard replies in his clear, easy style, so different from the scholastic discussion in Bacon’s corresponding passages. “If it was magic, the enchantment was worked by violence of nature rather than of waters. For although four elements compose the body of this world of sense, they are so united by natural affection that, as no one of them desires to exist without another, so no place is or can be void of them. Therefore immediately one of them leaves its position, another succeeds it without interval, nor can one leave its place unless some other which is especially attached to it can succeed it.” Hence it is futile to give the water a chance to escape unless you give the air a chance to enter. Be it noted that Adelard not only thus anticipates the theory of universal continuity, but also in the last clause of the quotation approaches the doctrine of chemical affinity in the formation and disintegration of molecules. Finally, he describes what actually occurs in the experiment more accurately than Roger Bacon or the other physicists cited by Duhem. “Hence it comes about that, if in a vessel which is absolutely tight above an aperture is made below, the liquid flows out only interruptedly and with bubbling. For as much air gets in as liquid goes out, and this air, since it finds the water porous, by its own properties of tenuity and lightness makes its way to the top of the vessel and occupies what seems to be a vacuum.” [Sidenote: Experiment and magic.]