The Tympanum and Scoop Wheel.

111

Chap. 14.]

ed, and its having been described as represented in the last figure by aRoman philosopher and engineer; it was most likely used as thus con-structed, tbrough tbe remote ages of antiquity, to the early part of the lastCentury, when a member of the Royal Academy of Sciences, of France ,M. De La Faye, developed by geometrical reasoning, a beautiful andtruly philosophical improvement. It is described by Belidor , (Tom.ii, 385,

No. 45. Tympanum improved by La Faye.

387,) together with the process of reasoning that led to it “ When thecircumference of a circle is developed ; a curve is described, (the invo-lute) of which all the radii are so many tangents to the circle ; and arelikewise all respectively perpendicular to the several points of the curve de-scribed, which has for its greatest radius, a line equal to the periphery ofthe circle evolved. Hence, having an axle whose circumference a littleexceeds the height which the water is proposed to be elevated, let thecircumference of the axle be evolved, and make a curved canal, whosecurvature shall coincide throughout exactly with that of the involute justformed; if the further extremity of this canal be made to enter the waterthat is to be elevated, and the other extremity abut upon the shaft whichis turned ; then in the course of rotation, the water will rise in a verticalmhection, tangential to the shaft, and perpendicular to the canal, in what-ever position it may be.” See No. 45.

The above figure from Belidor , is composedof four tubes only, but it is frequently con-tructed with double the number. Instead oftubes, curved partitions between the closed sidesof the wheel are offener used, as in the scoopwheel —which consists of a number of semi-circular partitions, extending from the axle tothe circumference of a large flat cylinder. Asit revolves in the direction of the arrows, the ex-tremities of the partitions dip into the water,and scoop it up, and as they ascend, dischargeNo. 46. Scoop Wheel. it into a trough placed under one end of theshaft, which is hollowed into as many compart-Ments as there are partitions or scoops. Wheels of this description, andpropelied by steam, are extensively used to drain the fens of Lincolnshire.