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64. and by that means it had only 3 on one side wch could receive ye impression of ye wind without being hindered by ye 3 of ye other side: But that engine could not be made in great because of ye enormous greatness wch must be given to ye semicylindrick circumference and that it would be in danger to be carried away by a moderate violent wind: I have seen also a model of horizontal windmills wch are of that sort wch is said to be in use in China, they are made like a lanterne, there is many sayls wch turn upon ye pivots towards ye center, and ye opposite point towards ye top, and ye incounterings wch stop them in certain situations to receive ye wind as directly as may be, and when these sayls have made a half turn by ye revolution of ye engine, they turn and come to ye wind, as weather-cocks and they there receive but small impression not to hinder those wch are on ye other side where ye wind incounters them directly or near it; and to that end those of ye other side receive ye wind but very obliquely, and by that means ye wind acts allways near twice more on one side than ye other, wch makes a sufficient effect to ye whole engine whose (essien) [[space]] is placed in ye middle of ye millstone wch is below wherefore it is not necessary to apply to its wheels and [[?lankiness]] as to other mills by ye rubbing of wch ye forces is diminished: We may by ye same method above calculate ye swiftness of ye wind wch is necessary to overturn trees or pillors wch should be placed at ye end without sustaining anything; here is examples Let there be a square of wood A B C D as that of a frame of paper of a foot large whose weight may be one pound and 1/4 or 20 ounces with its paper neck, exposed directly to ye wind and place perpendicular upon an horizontal plane, and having ye four small square sticks of an inch large. Then a wind of 12 feet in a second striking it will sustain near 6 ounces as hath been shewn above, and because it is but 12 lines thick, ye half thickness where its center of gravity is shall be but 6 lines: For ye weight of ye paper is not considered and because ye distance of its center of gravity to ye [[?supper]] is 6 inches, that wind shall act like a lever as 5 inches to 6 lines or as 12 to 1, and E F being ye axis of ye motion, ye proportion of ye force of ye wind against ye weight of ye square of 29 ounces, shall be as 72 ounces ye product of 6 ounces by 12 to 20 ounces, there must be therefore a lesser wind to make an equilibrium and if we take that of 6 feet in a second, it will have but ye fourth of 72 ounces viz 18 ounces and if 36 ye sq: of 6 gives 18, 40 will give 20 ounces, ye square foot of 40 is something more than 6 1/3 there will need therefore a wind wch makes 6 1/2 there will need therefore a wind wch makes 6 1/3 feet in a second to overturn this square frame: I have made ye experiment at ye top of ye observatory and in ye Samaritane: [[image: Three dimensional block shape annotated A B C D E F]] After ye same manner will be calculated ye force wch is necessary to break ye branch of a tree of half a foot thickness having ye arm 15 feet and 30 feet of [[?various]] branches and leaves shall be 900 superficiall feet wch ye wind will shoc ye absolute resistance of ye branch to be broken shall be 207360 by drawing ye height into ye base for ye absolute resistance of a stick of three lines hath been found to be 350 pound, A B is ye arm of ye branch D E F B ye compass of ye branches and leaves, and C ye center ye distance A C is 30 feet ye proportion of 30 feet to ye 30 of ye thickness towards A wch is but 2 inches is of 180 to 1 dividing 207360 by 180 ye quotient shall be 1152 there is need therefore of ye value of 1152 pounds to break ye branch in A there is 900 superficiall feet in ye leaves and branches of ye tree, and because 2 superficiall feet stroke by a wind of 12 feet in a second sustain 3/4 of a
Transcription Notes:
mandc: Reviewed. "essien" may mean "axis" but blank never filled in.
Image from Desaguliers: http://echo.mpiwg-berlin.mpg.de/ECHOdocuView?url=%2Fpermanent%2Flibrary%2FQERNH1MN%2Fpageimg&start=11&mode=imagepath&pn=211&ww=0.134&wh=0.2153&wx=0.8162&wy=0.1851
