Mechanics.

213

to have an equal Momentum , or to produce the sameEffect as in the Overjhot or Breajl-Whecl. Whence agreater Expence of Water will be made here, than inany other Sort of Mill, and can only be supplied for aConstancy by a River ; and where there is not a Wantof Water, this is the easiest, cheapest, and most simpleStructure a Mill is capable of.

23. In this Cafe, the Float-Boards are to be placedperpendicular to the Sole or Periphery of the Wheel,because when they come into a vertical Position at theBottom or lowest Part of the Wheel, they will then re-ceive the horizontal Er pet us of the Water directly, andtherefore with the greatest Force. If the Water-Coursebe sufficient to cover the Float-Boards, that is enough ;all that is more, runs waste, either by the Sides orunder the Floats, or both.

24. Let XYZ be an Underfhot-Whecl, and PIC the pj jfjjjWater coming upon it in the Direction HC. Now ifthere were so few Float-Boards, that when one, as **

DE, became vertical, the next on each Side IK, LM,should but just touch the Surface of the current Water,then would the Water strike the said Float-Board DEwith all its Force. But when the two Floats K and Ecome into the Situation C and G, then will the Waterstrike but a Part of the Float C, viz. BC, and that tooobliquely, which is to be estimated by A C, the Sine ofthe Angle of Incidence; and since we suppose theSection of the Water equal to the Area of a Float-Board, it is plain the Float C will intercept the Waterfrom the Float G, so that none can strike it; and there-fore the Force of Water will be every where less thanupon the Float-Board in the Site D E. So that theForce upon the Wheel will always be fluctuating be-tween AC and DE, which will be the two Extremes.

25. If the Float-Boards are so many, that while oneis vertical as DE, others on each S de, as C and G,are also partly in the Water-Way ; then in this Cafe itis best to have the Stream of Water larger than theFloats, that some may run beside, and fill up the Spacebetween, that so the Floats C, E, G, mav all be im-pell’d at once ; for the Back-Water, here, having agreater Velocity than that of the Wheel, will still ke- p

P 3 the

O.J