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IN 1738 BOURNELLI expounded his theory of hydrodynamics. He was concerned with the explanation of why water running through a pipe constricted somewhere in its course seemed to leave at the same speed and in the same quantity as it entered. What took place at the constricted section? Certainly the water must speed up there. What caused this increased flow? He reasoned that the internal pressure at the constricted section must be lower than elsewhere along the pipe, and he actually proved this theory by setting up a series of water gages along the course of this pipe. The same phenomenon was found to prevail with reference to gases. In other words, a rapidly moving body of fluids or gases always has a lower internal pressure than that same substance in a state of rest or slower motion. The more rapid the movement the lower the internal pressure.
N. VERN PETERSON. AERODYNAMICS IN THE PHYSIOLOGY OF THE UPPER RESPIRATORY TRACT. Arch Otolaryngol. 1947;45(1):117–120. doi:10.1001/archotol.1947.00690010124011