WIND-MILL. 



equidiltant from each other by their centre-pins being fitted 

 into a circular hoop : by thefe means, though the head of the 

 mill with the wheels and fails weigh feveral tons, they can be 

 made to turn round to face the wind by a flight power. 



The head is contrived to turn itfelf about w henever the wind 

 changes in the following manner : — A fmall pair of fails, or 

 fans, M, are fixed up in a frame L, projefting from the back 

 of the head : it has a pinion often leaves upon its axis, engag- 

 ing in a wheel of 60 teeth upon an incUned axis b ; and this 

 has a pinion doi 1 2 leaves at the other end of it, turning a bevil- 

 led wheel of 72 teeth upon a vertical iron axis, at the lower 

 end of which is a pinion e oi 11 teeth : this works in a circle 

 of 1 20 cogs, fixed round on the outfide of the fixed kirb. By 

 thefe means, whenever the fan M is turned, it moves the head 

 of the mill (lowly round, and with proportionate power. 



Now if ever the wind varies in the leaft from the direftion 

 of the main fliaft of the fails, it afts obliquely upon the 

 »anes of the fan, and turns them round, at the fame time 

 fetting the head right again, fo that the axis points to the 

 wind. But when the axis is in this fituation, the wind blows 

 in the planes of the vanes of the fan, and has no effeft upon 

 them. The head of the mill is kept firmly in its place when 

 it turns about by rollers ; the axles of which are bolted 

 to the infide of the framing of the head, and the rollers 

 apply to the infide of the fixed kirb : there are four of thefe 

 rollers. The pivot at the upper end of the vertical fliaft is 

 fupported in a bearing bolted to a crofs-beam in the framing 

 of the head of the mill ; and this is fixed precifely in the 

 centre of the head, that it may not vary in its fituation as 

 the head turns round. Many other things are fo evident in 

 the drawing as to need little farther explanation ; fuch as 

 the different floors of the building, and the circular gallery, 

 I I, all round the mill, for the miller to go round to take the 

 cloth off the fails in high winds, or when the mill is to ftop. 

 This is done by untying the cloth at the extremity of the 

 fail, and twifting it up like a rope ; then tying the end of 

 it again to the lattice, in which ftate it prefents no furface to 

 the wind. At i is a roller turned round by a wheel /, fixed 

 on the middle part of the vertical fliaft : it is ufed to draw 

 up the facks of corn from the bottom of the mill into the 

 upper part, which is ufed as a ftore-houfe for the corn, be- 

 ing divided into as many compartments as the miller requires. 

 The miU-ftones are made the fame as thofe ufed in water- 

 mills. A pairof regulating balls areattached to the upperpart 

 of the miU-ftone fpindle, to regulate the velocity of the mill. 

 The manner of applying this regulator is explained in Jig. 5. 

 Piatt II. Wind-Mill. The lower end of the iron fpindle 

 F is fitted to a fquare, formed on the top of the mill-fl:one 

 axis, and the pinion ^^ is fixed on the upper end, to give mo- 

 tion to the ftones : immediately beneath the pinion two rods 

 are jointed, hanging downwards, having a heavy iron ball, I, 

 fixed faft on the lower end of eacli : two links are jointed to 

 the arms at m, and fufpend a collar, which is capable of 

 Aiding freely up and down upon the fpindle F. It is evident 

 that when the balls fly out from the fpindle by their centri- 

 fugal force, that the collar will be elevated, and the con- 

 trary when the balls approach the fpindle. Tlie Aiding col- 

 lar is embraced by a fork formed at the end of a fteelyard, 

 lying horizontal, and fufpended by the rod^ as a fulcrum ; 

 an iron rod y defcends from the extreme end of the fl;eelyard, 

 baving its lower end formed to a hook, by which it is con- 

 nefted with a lever, r, whofe fulcrum is j ; this, by an iron 

 rod t, fufpends one end of the beam called the bridge, on 

 ■which the lower pivot of the miU-ftone axis refts, the other 

 end bearing on a fulcrum or centre. Now it follows from 

 this arrangement of levers, that by elevating the forked end 



of the fteelyard, or tlie Aiding collar, that tlie fpindle o^ 

 the ftones will be fuffered to defcend a very minute quantity. 

 This regulates the velocity of the mill, becaufe when the 

 wind increafes, and the motion of the mill is accelerated, the 

 balls fly out by the centrifugal force ; this lets the upper 

 ftone down nearer to the lower, thereby increafing the re- 

 fiftance to the mill, and counterafting the increafed force of 

 the wind. On the other hand, if the wind falls, and the 

 mill moves more flowly in confequence, the balls fall toge- 

 ther, and let down the Aiding collar; this raifes the ftone 

 up, and increafes tlie diftance between them, thereby dimi- 

 niftiing the refittance ; for this pnrpofe, a weight i ^g. 5.) 

 is hung upon the fteelyard, fufiicient to elevate the ftone 

 whenever the clofing of the balls and confequent defcent of 

 the collar will permit it to do fo. There are feveral notches 

 made in the fteelyard for different pofitions of the fulcrum p 

 and rod q ; by means of thefe the quantity of the regulation 

 can be adjufted to the following rule. If when the wind 

 blows ftronger the mill goes flower, contrary to the effeft 

 expefted, it ftiews that the regulation is too a£tive ; then in- 

 creafe the leverage of the balls by ftiortening the diftance 

 between the fulcrum p of the fteelyard and the fufpenfion 

 of the rod q, by ftiifting either of them into different 

 notches. On the contrary, if the mill goes much fafter 

 when the wind increafes, it fliews that the regulation does 

 not aft fufiSciently ; then increafe the diftance between the 

 rod q and the fulcrum p. If the whole limits of the 

 notches in the fteelyard fliould not be fufEcient to effeft 

 this, the afting length of the lever rs muft be increafed or 

 diminiflied by removing its fulcrum / to a greater or leffer 

 diftance from the fufpending-rod / ; by means of this con- 

 trivance the miller is enabled, without mnch inconvenience, 

 to regulate the velocity of the ftones to that degree which 

 is found beft for reducing the greateit quantity of grain to 

 flour, without damaging it by heating, as is the cafe when 

 the ftones move too quick. 



Theory of the Motion of a Wind- Mil!, ivith the Poftion of 

 its Sails or Vanes. — The angle which the furfaces of the fails 

 are to make with their common axis, that the wind may have 

 the greateft effeft, or the degree of weathering, as the mill- 

 wrights call it, is a matter of nice inquiry, and has much 

 employed the thoughts of the mathematicians. 



To conceive why a wind-mill moves at all, the theory of 

 compound motions muft be fuppofed. A body moving 

 perpendicularly againft any furface, ftrikes it with all its 

 force. If it move parallel to the furface, it does not ftrike 

 it at all : and if it move obliquely, its motion, being com- 

 pounded of the perpendicular and parallel motion, only afts 

 on the furface, confidered as it is perpendicular, and only 

 drives it in the direftion of the perpendicular. So that 

 every oblique direftion of a motion is the diagonal of a 

 parallelogram, whofe perpendicular and parallel direftions 

 are the two fides. Add, that if a furface, which, being 

 ftruck obhquely, has only received the perpendicular direc- 

 tion, be fattened to fome other body, fo as that it cannot 

 purfue its perpendicular direftion, but muft change it for 

 fome other ; in that cafe, the perpendicular itfelf becomes 

 the diagonal of a new parallelogram, one of whofe fides is 

 the direftion which the furface may follow ; and the other, 

 that which it cannot. 



Thus, a rudder fattened obliquely to the keel of a veffel, 

 being ftruck by the current of water parallel to the keel, 

 and, of confequence, obliquely with regard to itfelf; it 

 will appear, by drawing the line of perpendicular impulfe, 

 that it tends to tear the rudder from the keel, and to carry 

 it away : and that this direftion, perpendicular to the rud- 

 der, 



