The demonstration apparatus below is variously called Segner's Reaction Turbine, Parent's Mill, the Scotch Turbine, the Hydraulic Tourniquet or Barker's Mill. It was probably first invented in 1760 by Andreas Segner using Hero's steam reaction turbine as a model. Water from above pours into the funnel at the top of the central rotor, pivoting freely about its axis. Projecting from the bottom of the rotor are two pipes, each closed at the end, but with a rearward-facing hole. Water spouts out of these holes, making the rotor spin.
We can all have sympathy with the author of the 1856 Benjamin,
Pike, Jr. Catalogue who wrote that "the action of the machine does not,
as sometimes stated, depend on the resistance of the atmosphere to the
jet from the cross-pipe, but is wholly owing to the hydrostatic pressure
of the column of water on the vertical tube." The ready acceptance of jet
and rocket propulsion has not made students any less likely to have trouble
with Newton's third law.
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