406 KJNEMA TICS OF MA CHINEE Y.
cylindric ring whose inner and outer radii are those of the bottom and top of the teeth respectively, the annular space, that is, between the point and root cylinders. This we may call shortly the tooth-ring.
If, therefore, it be desired to increase the amount of water delivered per revolution without changing the diameter of any part of the wheel, it is only necessary to lengthen a and I in the direction of their axes. If the head of water be not great, and the angular velocity of the wheels not too small,, careful construction may so reduce the loss of water as to make it not worth considering. The arrangement, therefore, is one which in many cases may furnish a really useful water-pump.
As a pump, indeed, the machine is already very old. Weisbach calls it* Bramah's rotary pump, and says that Leclerc improved it (by placing packing wedges in the ends of the teeth) ; other writers ascribe it to Leclerc himself. This would take back the date of the invention to the end of the last century. But long before this, in 1724, the pump had been described as old by Leupold,f and called "Machina Pappenheimiana" ; he headed it "A chamber ap- paratus with two moving wheels, called by D. Becher Machina Pappenheimiana," Now Becher's work J appeared in the first half of the 17th century. Besjfes this, however, Kircher, Schott, Leurechin, and also Schwenter, in his " Mathematischen Erquickstunden " (A.D. 1636, p. 485), have described the same machine with the alteration that the wheels have four teeth instead of six, and that they do not name Pappenheim. The machine is now therefore over 230 years old ; it was already known in the time of the Thirty Years' War, and all accounts agree in making it a (ir^rman invention. Whether Pappenheim was the name of its inventor, or of his city only, remains uncertain ; we are quite justi- fied, however, in any case in calling it the Pappenheim pump. In France Grollier de Servieres (1719) is often named as its inventor.|| But this date is that only of the appearance of a description by the yt>unger de Servieres of the mechanical collection of his grandfather,
- Weisbach, Mechanik, iii.,p. 843. t Theatrum Macli. ffydraul, vol. i., p. 123.
Trifolium Ilecherianum, which is unfortunately not to be found either in the Konigl. Bibliothek in Berlin or in the Library of the British Museum.
Kasper Schott, Mechanica Hydraulica Pneumatica, Mainz, 1657. The wheels shown in a little copper-plate engraving have here nineteen teeth.
|| Propay. fndustr., 1868, iii.,'p. 20.
