Windmill: Wikis


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From Wikipedia, the free encyclopedia

This Dutch windmill in Amsterdam was built in 1757 and is identified as De 1100 Roe. It is a smock mill of the type called by the Dutch a grondzeiler ("ground sailer"), since the sails almost reach the ground.

A windmill is a machine which converts the energy of wind to rotational motion by means of adjustable vanes called sails. The main use is for a grinding mill powered by the wind, reducing a solid or coarse substance into pulp or minute grains, by crushing, grinding, or pressing.[1][2] Windmills have also provided energy to sawmills, paper mills, hammermills, and windpumps for obtaining fresh water from underground or for drainage (especially of land below sea level).



The windmills of Campo de Criptana were immortalized in chapter VIII of Don Quixote.

The windwheel of Heron of Alexandria in the 1st century marks one of the first known instances of wind powering a machine in history.[3][4] Another early example of a wind-driven wheel was the prayer wheel, which was used in ancient Tibet and China since the 4th century.[5]


Vertical-axis windmills

The first practical windmills were the vertical axle windmills invented in eastern Persia, as recorded by the Persian geographer Estakhri in the 9th century.[6][7] The authenticity of an earlier anecdote of a windmill involving the second caliph Umar (AD 634–644) is questioned on the grounds that it appears in a 10th-century document.[8] Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water, and were quite different from the later European horizontal-axis versions. Windmills were in widespread use across the Middle East and Central Asia, and later spread to China and India from there.[9]

Some popular treatments of the subject have speculated that, by the 9th century, the Afghanistan-style vertical-axle mills spread to Europe through Al-Andalus (Islamic Spain).[10] This has been denied by the specialist of medieval European technology, Lynn White Jr., who points out that there is no evidence (archaeological or documentary) that the Afghanistan-style vertical-axle windmill spread as far west as Al-Andalus,[11] and notes that "all Iberian windmills rotated on horizontal axles until towards the middle of the fifteenth century."[12] Another historian of technology, Michael Jonathan Taunton Lewis, suggested an alternative route of transmission for the Islamic horizontal-shaft windmill, with its diffusion to the Byzantine Empire and its subsequent transformation into the vertical-shaft windmill in Europe.[13] Late medieval verticle-axle windmills similar to the Islamic/Persian design can be found along this route, particularly in Karpathos, Greece, and Kandia, Crete. The Crusades has also been suggested as another possible route of transmission, though in the sense of "stimulus diffusion," where the idea was diffused rather than the technology itself.[14] However, the debate about whether the European vertical-shaft windmill evolved from the Islamic horizontal-shaft windmill or was an independent development remains unresolved.[13]

Horizontal-axis windmills

Medieval depiction of a windmill

Fixed windmills, oriented to the prevailing wind were extensively used in the Cyclades islands of Greece. The economies of power and transport allowed the use of these 'offshore' mills for grinding grain transported from the mainland and flour returned. A 1/10th share of the flour was paid to the miller in return for his service. This type would mount triangular sails when in operation.[citation needed]

A similar type of vertical-shaft windmill with rectangle blades, used for irrigation, can also be found in 13th-century China (during the Jurchen Jin Dynasty in the north), introduced by the travels of Yelü Chucai to Turkestan in 1219.[15]

Horizontal-axle windmills that turn to face the wind

In northwestern Europe, the horizontal-axle or vertical windmill (so called due to the dimension of the movement of its sails) dates from the last quarter of the 12th century in the triangle of northern France, eastern England and Flanders. Lynn White Jr. claims that the first certain reference to the European horizontal-axle windmill is dated to 1185 in Weedley, Yorkshire.[16] (This predates Joseph Needham's claim that the earliest known reference is from the 1191 chronicle of Jocelin of Brakelond, in which a Dean Herbert of East Anglia supposedly competed with the mills of the abbey of Bury St Edmunds).[17] These earliest mills were used to grind cereals. The evidence at present is that the earliest type was the sunk post mill, so named because of the large upright post on which the mill's main structure (the "body" or "buck") is balanced. By mounting the body this way, the mill is able to rotate to face the wind direction; an essential requirement for windmills to operate economically in North-Western Europe, where wind directions are variable. By the end of the thirteenth century the masonry tower mill, on which only the timber cap rotated rather than the whole body of the mill, had been introduced. In the Netherlands these stone towerlike mills are called "round or eight-sided stone stage mills, ground-sailers (windmills with sails reaching almost down to the ground), mound mills, etc." (Dutch: ronde/achtkante stenen stelling molens, grond-zeilers, beltmolens, etc.). Dutch tower mills ("torenmolens") are always cylindrical (such as atop castle or city wall towers). Because only the cap of the tower mill needed to be turned the main structure could be made much taller, allowing the sails to be made longer, which enabled them to provide useful work even in low winds. Such mills often have a small auxiliary set of sails called a fantail at the rear of the cap and at right angles to the sails; this rotates the cap through gearing so the sails face into the wind.

  • Post mills in Germany are Bockwindmühlen, Paltrockmühlen or Wippmühlen.
  • Smock mills in Germany can be Sockelgeschoßholländer or Galerieholländer.
  • Tower mills in Germany can be Turmholländer, Galerieholländer, Erdholländer or Bergholländer

Windmills were often built atop castle towers or city walls, and were a unique part of a number of fortifications in New France, such as at Fort Senneville.

Diagram of the smock mill at Meopham, Kent which uses a fantail and Cubitt's patent sails

The familiar lattice style of windmill sails (also called "common" sails) allowed the miller to attach sailcloths to the sails (while applying a brake). Trimming the sails allowed the windmill to turn at near the optimal speed in a large range of wind velocities. The fantail, a small windmill mounted at right angles to the main sails which automatically turns the heavy cap and main sails into the wind, was invented by Edmund Lee in 1745, in England. The smock mill is a later variation of the tower mill, constructed of timber and originally developed in the sixteenth century for land drainage. With some subsequent development mills became versatile in windy regions for all kind of industry, most notably grain grinding mills, sawmills (late 16th century), threshing, and, by applying scoop wheels, Archimedes screws, and piston pumps, pumping water either for land drainage or for water supply. In 1772, Scottish millwright, Andrew Meikle developed the spring sail made from a series of connected parallel shutters that could be opened or closed according to windspeed. To do this the sails had to be stopped, but the sails also incorporated a spring which allowed the shutters to open a little more to prevent damage if the wind suddenly strengthens. In 1789, Stephen Hooper invented the roller reefing sail, which allowed automatic adjustment of the sail whilst in motion. In 1807, William Cubitt a Norfolk engineer, invented a new type of sail, known there on as patent sails, using a chain and a rod that passed through the centre of the windshaft. These sails had the shutters of Meikle's spring sails and the automatic adjustment of Hooper's roller reefing sails. This became the basis of self-regulating sails. These avoided the constant supervision that had been required up till then.

A windmill on the background of the 1792 Battle of Valmy, France.

By the 19th Century there were some 10,000 corn mills operating in Britain,[18] but with the coming of the industrial revolution, the importance of wind as primary industrial energy source was replaced by steam and internal combustion engines. The increased use of steam, and later diesel power, however, had a lesser effect on the mills of the Norfolk Broads, these being so isolated (on extensive uninhabitable marshland) that some of them continued in use as drainage pumps powered by diesel until as late as 1959. More recently windmills have been preserved for their historic value, in some cases as static exhibits when the antique machinery is too fragile to put in motion, and in other cases as fully working mills. There are around 50 working mills in operation in Britain as of 2009.[18]

Such was the importance of the corn mills of Britain that a number of phrases used in their operation have found their way into common usage in the English language: When the wind was not strong enough to turn the sails the millstones would "grind to a halt", and the coarseness of the ground flour was assessed by the miller rubbing it between his thumb and forefinger, giving rise to the term "rule of thumb".[18]

See Flood control in the Netherlands for use of windmills in land reclamation in the Netherlands.

In Canada and the United States

An isometric drawing of the machinery of the Beebe Windmill. It was built in Bridgehampton, NY in 1820.

Windmills feature uniquely in the history of New France, particularly in Canada, where they were used as strong points in fortifications.[19] Prior to the 1690 Battle of Québec, the strong point of the city's landward defenses was a windmill called Mont-Carmel, where a three-gun battery was in place.[19] At Fort Senneville, a large stone windmill was built on a hill by late 1686, doubling as a watch tower.[20] This windmill was like no other in New France, with thick walls, square loopholes for muskets, with machicolation at the top for pouring lethally hot liquids and rocks onto attackers.[20] This helped make it the "most substantial castle-like fort" near Montreal.[21]

In the United States, the development of the water-pumping windmill was the major factor in allowing the farming and ranching of vast areas of North America, which were otherwise devoid of readily accessible water. They contributed to the expansion of rail transport systems throughout the world, by pumping water from wells to supply the needs of the steam locomotives of those early times. Two prominent brands were the Eclipse Windmill developed in 1867 (which was later bought by Fairbanks-Morse) and the Aermotor, which first appeared in 1888 and is still in production. The effectiveness of the Aermotor's automatic governor, which prevents it from flying apart in a windstorm, led to its popularity over other models. Currently, the Aermotor windmill company is the only remaining water windmill manufacturer in the United States. They continue to be used in areas of the world where a connection to electric power lines is not a realistic option.[22]

The multi-bladed wind turbine atop a lattice tower made of wood or steel was, for many years, a fixture of the landscape throughout rural America. These mills, made by a variety of manufacturers, featured a large number of blades so that they would turn slowly with considerable torque in low winds and be self regulating in high winds. A tower-top gearbox and crankshaft converted the rotary motion into reciprocating strokes carried downward through a rod to the pump cylinder below.

Windmills and related equipment are still manufactured and installed today on farms and ranches, usually in remote parts of the western United States where electric power is not readily available. The arrival of electricity in rural areas, brought by the Rural Electrification Administration (REA) in the 1930s through 1950s, contributed to the decline in the use of windmills in the US. Today, the increases in energy prices and the expense of replacing electric pumps has led to an increase in the repair, restoration and installation of new windmills.

1980's Wind Energy Experiment

In the early 1980s, several small companies started wind farms for commercial energy production in the San Joaquin valley region of California. The first such wind farm was created in 1981 when John Eckland, of Fayette Manufacturing Corporation placed the first windmills on land leased from Joe Jess, Sr. on the Altamont Pass. Later, as a gift to Mr. Jess for the continued use of his land, Fayette created a ‘stars and stripes’ themed windmill for Mr. Jess.[23][24][25]

At one point in the mid-80’s there were over twenty-six wind farm companies operating in this area of the United States. This eventually expanded to areas outside of Palm Springs, as seen as backdrops in several films of the era, such as Less Than Zero. However, later legislative efforts by California lawmakers eliminated the financial incentives and tax breaks that made these early alternative energy projects feasible (Fisher, 1985). Similar tax credits and incentives have brought a resurgence in interest in renewable energy sources in other areas of the country (Maloney, 2006).[23][24][25]

Multi-sailed windmills

An eight sailed Windmill at Heckington, Lincolnshire, UK

The majority of windmills had four sails. An increase in the number of sails meant that an increase in power could be obtained, at the expense of an increase in the weight of the sail assembly. The earliest record of a multi-sailed mill in the United Kingdom was the five sail Flint Mill, Leeds, mentioned in a report by John Smeaton in 1774. Multi-sailed windmills were said to run smoother than four sail windmills. In Lincolnshire, more multi-sailed windmills were found than anywhere else in the United Kingdom. There were five, six and eight sail windmills.[26]

If a four sail windmill suffers a damaged sail, the one opposite can be removed and the mill will work with two sails, generating about 60% of the power that it would with all four sails. A six sail mill can run with two, three, four or six sails. An eight sail mill can run with two, four, six or eight sails, thus allowing a number of options if an accident occurs. A five sail mill can only run with all five sails. If one is damaged then the mill is stopped until it is replaced.[26] Apart from the UK, multi-sail mills were built in Malta and the USA.

See also


  1. ^ Mill definition
  2. ^ Windmill definition stating that a windmill is a mill or machine operated by the wind
  3. ^ A.G. Drachmann, "Heron's Windmill", Centaurus, 7 (1961), pp. 145-151
  4. ^ Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995), pp.1-30 (10f.)
  5. ^ Lucas, Adam (2006), Wind, Water, Work: Ancient and Medieval Milling Technology, Brill Publishers, p. 105, ISBN 9004146490 
  6. ^ دانره المعارف بزرگ اسلامی - اصطخري‌، ابواسحاق‌
  7. ^ Ahmad Y Hassan, Donald Routledge Hill (1986). Islamic Technology: An illustrated history, p. 54. Cambridge University Press. ISBN 0-521-42239-6.
  8. ^ Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995), pp.1-30 (8)
  9. ^ Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69. (cf. Donald Routledge Hill, Mechanical Engineering)
  10. ^ Farrokh, Kaveh (2007), Shadows in the Desert, Osprey Publishing, p. 280, ISBN 1846031087 
  11. ^ Lynn White Jr. Medieval technology and social change (Oxford, 1962) p. 86
  12. ^ Lynn White Jr. Medieval technology and social change (Oxford, 1962) p. 161-162
  13. ^ a b Lucas, Adam (2006), Wind, Water, Work: Ancient and Medieval Milling Technology, Brill Publishers, pp. 106-7, ISBN 9004146490 
  14. ^ Bent Sorensen (November 1995), "History of, and Recent Progress in, Wind-Energy Utilization", Annual Review of Energy and the Environment 20: 387-424, doi:10.1146/ 
  15. ^ Needham, Volume 4, Part 2, 560.
  16. ^ Lynn White Jr. Medieval technology and social change, Oxford, 1962, p. 87.
  17. ^ Needham, Volume 4, Part 2, 555.
  18. ^ a b c Episode 1: Directed and produced by Naomi Benson: BBC Television
  19. ^ a b Chartrand, French Fortresses in North America 1535–1763: Québec, Montréal, Louisbourg and New Orleans
  20. ^ a b Chartrand, p 41
  21. ^ Chartrand, p. 38
  22. ^ Quirky old-style contraptions make water from wind on the mesas of West Texas
  23. ^ a b Land Use Cooperative article from 1985
  24. ^ a b (2006) Maloney, P. New York Times, May 17th. 2006.
  25. ^ a b The threat to wind energy, special report. (1985). Fisher, B. New York Times, October 26, 1985.
  26. ^ a b Wailes, Rex (1954). The English Windmill. London: Routlege & Kegan Paul. pp. 99–104. 


  • A.G. Drachmann: "Heron's Windmill," Centaurus, 7 (1961), pp. 145–151

Further reading

  • Ahmad Y Hassan, Donald Routledge Hill (1986). Islamic Technology: An illustrated history. Cambridge University Press. ISBN 0-521-42239-6.
  • Chartrand, French Fortresses in North America 1535–1763: Québec, Montréal, Louisbourg and New Orleans.
  • Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995)
  • A.G. Drachmann, "Heron's Windmill", Centaurus, 7 (1961).
  • Needham, Joseph (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering. Taipei: Caves Books Ltd.
  • Hugh Pembroke Vowles: "An Enquiry into Origins of the Windmill", Journal of the Newcomen Society, Vol. 11 (1930-31)
  • Roy Gregory and Laurence Turner (2009) Windmills of Yorkshire ISBN 9781840334753
  • Edwin Tunis (1999), Colonial living, The Johns Hopkins University Press ", ISBN 0-8018-6627-2, pp. 72 and 73

External links

Source material

Up to date as of January 22, 2010
(Redirected to The Windmill article)

From Wikisource

The Windmill
by Henry Wadsworth Longfellow
From Ultima Thule.

Behold! a giant am I!
Aloft here in my tower,
With my granite jaws I devour
The maize, and the wheat, and the rye,
And grind them into flour.

I look down over the farms;
In the fields of grain I see
The harvest that is to be,
And I fling to the air my arms,
For I know it is all for me.

I hear the sound of flails
Far off, from the threshing-floors
In barns, with their open doors,
And the wind, the wind in my sails,
Louder and louder roars.

I stand here in my place,
With my foot on the rock below,
And whichever way it may blow
I meet it face to face,
As a brave man meets his foe.

And while we wrestle and strive
My master, the miller, stands
And feeds me with his hands;
For he knows who makes him thrive,
Who makes him lord of lands.

On Sundays I take my rest;
Church-going bells begin
Their low, melodious din;
I cross my arms on my breast,
And all is peace within.

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

WINDMILL, a term used, in the widest sense, for a machine by which the energy of the wind is applied to useful purposes. Windmills were certainly used as early as the 12th century and are still largely employed in Holland i n draining t h e polders and grinding trass. They are somewhat extensively used in America for pumping and driving agric ult u ral machinery. In spite of the competition of more powerful and tractable motors, they are serviceable, especially in new countries, where fuel is scarce and where work can be done intermittently. An inquiry was made in India in 1879 as to the possibility of using windmills for irrigation (Professional Papers on Indian Engineering, July 1879), with the result that it was concluded their usefulness would be very limited.

A windmill is not in any case a very powerful or efficient motor, and its work is variable and intermittent. In favourable positions, it will run on an average for eight hours out of the twenty-four. For pumping on a small scale, the intermittent action is least an objection, because there is generally a tank or storage reservoir regulating the delivery of the water. For driving dynamos windmills are least suitable, on account of the variation of speed, though some attempts to generate electricity by wind power have been made, special arrangements being adopted for automatically regulating the speed.

European Windmills

In all the older windmills a shaft, called the wind shaft, carried four to six arms or whips on which long rectangular narrow sails were spread. The wind shaft was placed at an inclination of 10° or 15° with the horizontal, to enable the sails to clear the lower part of the mill. The whip carrying the sail was often 30 to 40 ft. in length, so that the tips of the sails described a circle 60 to 80 ft. in diameter. The sails were rectangular, 5 to 6 ft. wide, and occupying five-sixths of the length of the whip. A triangular leading sail was sometimes added. Sometimes the sails consisted of a sail-cloth spread on a framework; at other times narrow boards were used. The oldest mill was no doubt the post mill, the whole structure being carried on a post; to bring the sails to face the wind, the structure was turned round by a long lever. The post mill was succeeded by the tower, smock or frock mill, in which the mill itself consisted of a stationary tower, and the wind shaft and sails were carried in a revolving cap rotating on the top of the tower. Andrew Meikle introduced in 1750 an auxiliary rotating fan at right angles to the principal sails, which came into action whenever the wind was oblique to the axis of the sails, automatically veering the sails or placing them normal to the wind. For safety, the sails must be reefed in high winds. In 1807, Sir W. Cubitt introduced automatic reefing arrangements. The sails were made of thin boards held up to the wind by weights. If the force of the wind exceeded a certain value the boards were pressed back and exposed little surface.

American Windmills

These generally have the sails, 18 or more in number, arranged in an annulus or disk. The sails consist of narrow boards or slats arranged radially, each board having a constant or variable inclination to the wind's direction. An American mill presents a larger surface for a given length of sail than the older type, and consequently the construction is lighter. To turn the mill face to the wind a rudder is sometimes used projecting backward in a plane at right angles to the plane of rotation of the sails. Various arrangements are adopted for reefing the sails automatically. (a) In some an action equivalent to reefing is obtained by turning the sail disk oblique to the wind. The pressure on a side vane in the plane of rotation, controlled by a weight, turns the sail disk edgeways to the wind if the pressure exceeds a safe amount. (b) In centrifugal governor mills the slats forming the sails are connected in sets of six or eight, each set being fixed to a bar at the middle of its length. By rotating this bar the slats are brought end on to the wind, the action being analogous to shutting an umbrella. The slats are held up to the wind by a weight. A centrifugal governor lifts the weight if the speed becomes excessive and the sails are partially or completely furled. Many of the veering and reefing arrangements are very ingenious and too complicated to be described without detailed drawings. A description of some of these arrangements will be found in a paper by J. A. Griffiths (Prot. Inst. Civ. Eng., 119, p. 321) and in a "Report on Trials of Wind Pumping Engines at Park Royal in 1903" (J ourn_ Roy. Agric., Soc., 64, p. 174).

Missing image

Warner's Annular Sail Windmill

Messrs Warner of London make a windmill somewhat similar to American mills. The shutters or vanes consist of a frame covered with canvas, and these are pivoted between two angle-iron rings so as to form an annular sail. The vanes are connected with spiral springs, which keep them up to the best angle of weather for light winds. If the strength of the wind increases, the vanes give to the wind, forcing back the springs, and thus the area on which the wind acts diminishes. In addition, there are a striking lever and tackle for setting the vanes edgeways to the wind when the mill is stopped or a storm is expected. The FIG. 1 - Windmill near Delft.

wheel is kept face to the wind by a rudder in small mills; in large mills a subsidiary fan and gear are used. Fig. 2 shows a large mill of this kind, erected in a similar manner to a tower mill. The tower is a framework of iron, and carries a revolving cap, on which the wind shaft is fixed. Behind is the subsidiary fan with its gearing acting on a toothed wheel fixed to the cap.

It is important that wind-mill should control itself so that it works efficiently in moderately strong winds and at the same time runs in very light winds, which are much more prevalent. It should also, by reefing or otherwise, secure safety in storms.

Table I. gives the mean velocity of the wind in miles per hour for an inland station, Kew, and a very exposed station, Scilly, for each month during the period 1890-1899.

The pressure of the wind on a plane normal to its direction, composed partly of an excess front pressure and negative back pressure, is given by the relation p=0.003 v2, where p is in pounds per square foot and v the velocity of the wind in miles per hour.

It varies a little with the form and size of the surface, but for the present purpose this variation may be disregarded. (See experiments by Dr Stanton at the National Physical Laboratory, Proc. Inst. Civ. Eng. 156, p. 78.) For velocities of 5, to and 20 m. per hour the pressures on a plane normal to the wind would be about 0.075, 0.3 and 1.2 lb per sq. ft. respectively, and these may be taken to be ordinary working velocities for windmills. In storms the pressures are much greater, and must be reckoned with in considering the stability of the mill. A favourable wind velocity for windmills is 15 m. per hour.







Kew .

8 o






Scilly .


19 5











Kew .



6 o




Scilly .







Table Pressure on Surfaces oblique to the Wind.-Let fig. 3 represent a plane at rest on which a wind current impinges in the direction YY, making an angle 0 with the normal Oa to the plane. Then the pressure n normal to the plane is given very approximately by Duchemin's rule n=p o cos + o lb per sq. ft.

where p is the pressure in pounds per square foot on a plane struck normally by the same wind.

In fig. 3 let AB be part of a windmill sail or vane at rest, XX being the plane of rotation and YY the direction of the wind. The angle 0 is termed the weather of the sail. This is generally a constant angle for the sail, but in some cases varies from a small angle at the outer end to a larger angle near y the axis of rotation. In.' mills of the European type, 0 = 12° to 18°, and the speed of the tips of the sails is 21 to 3 times the velocity of the wind. In mills of the American type, 0=28° to 40°, and the speed of the tips of the vanes is 4 to 1 time that of the wind. Then if Oa =n be the normal pressure on the sail or vane per square foot, ba=t is the effective component of pressure in the direction of rotation and 2 sin o cos t= n sin o- '1' -+-cos t B' When the sail is rotating in a plane at right angles to the wind direction the conditions are more complicated. In fig. 4 let XX be the plane of rotation of the vane and YY the direction of the wind. Let Oa be the normal to the vane, 0 being the weather of the vane. Let Ov =v be the velocity of the wind, Ou =u the velocity of the vane. Completing the parallelogram, Ov r =vr is the velocity and direction of the wind relatively to the vane.

y r = -4 (v 2 + u 2) = v sec 4), tan 4)=u/v, and the angle between the relative direction of wind and normal to the vane is 0+4). It is clear that 0+4 cannot be greater than 90°, or the vane would press on the wind instead of the wind on the vane. Substituting these values in the equations already given, the normal pressure on the oblique moving vane is 'n= 003 v2 sec2 cos(o-}-4) I +cos (o+4)) The component of this pressure in the direction of motion of the vane is sin (0+0) cos (0+0) t = 003 v 2 sec2¢ +cos t (o+0) and the work done in driving the vane is to =iv tan = 003 v 3 sec' 4) tan 45 sin (0+4)cos (0+0) I + cos t (0+4) foot lb per sq. ft. of vane per sec., where v is taken in miles per hour. For such angles and velocities as `are usual in windmills this would give for a square foot of vane, near the tip about 0.003 v 3 ft. lb perY sec. But parts of the vane or sail nearer the axis of rotation are less effective, and there are mechanical fric tion and other causes of ineffici ency. An old rule FIG. 4. based on experi ments by Coulomb on mills of the European type gave for the average effective work in foot lb per sec. per sq. ft. of sail W =o ooI I v3.







Revolutions of wheel .







Double strokes of pump







Gallons lifte







Average effective horse-power. .







Table -In 150 Working Hours. I. Goold Shapley and Muir, Ontario; wheel 16 ft. diameter, 18 vanes, 131 sq. ft. area (first prize). II. Thomas && Son (second prize). III. W. Titt. IV. R. Warner. V. W. Titt. VI. H. Sykes.

FIG. 2

.-Warner's Annular Sail Windmill.

Missing image
Missing image

X; Some data given by Wolff on mills of the American type gave for the same quantity W = o 00045v3.

From some of the data of experiments by Griffiths on mills of the American type used in pumping, the effective work in pumping when the mill was working in the best conditions amounted to from 0 0005v 3 to 0 0003v 3 ft. lb per sec. per sq. ft.

In 1903 trials of wind-pumping engines were carried out at Park Royal by the Royal Agricultural Society (Journ. Roy. Agric. Soc. lxiv. 174). The mills were run for two months altogether, pumping against a head of 200 ft. The final results on six of the best mills are given in Table II.

A valuable paper by J. A. Griffiths (Proc. Inst. Civ. Eng. cxix. 321) contains details of a number of windmills of American type used for pumping and the results of a series of trials. Table III. contains an abstract of the results of his observations on six types of windmills used for pumping: eastern doorway of the Erechtheum, which formed part of the original building of 430 B.C., have lately been found; they were rectangular windows with moulded and enriched architrave, resting on a sill and crowned with the cymatium moulding. Of later date, at Ephesus, remains of similar windows have been discovered. Of Roman windows many examples have been found, those of the Tabularium being the oldest known. A coin of Tiberius representing the temple of Concord shows features in the side wings which might be windows, but as statues are shown in them they are possibly only niches. Over the door of the Pantheon is an open bronze grating, which is thought to be the prototype of the windows which lighted the large halls of the Thermae, as it was absolutely necessary that these should be closed so as to retain the heat, the openings in the gratings being filled with glass. In some cases window openings were closed with thin slabs of marble, of which there are examples still existing in the churches of S. Martino and the Quattro Santi Incoronati at Rome. Similar slabs exist in the upper storey of the amphitheatre at Pola; it still remains, however, an open question TABLE III.







Diameter of wheel, feet. .







Sail area, square feet. .. .







Weather angle, outer ends. .. .

18° 47'






inner ends. .. .

38° 20'






Pitch of vanes, outer ends, feet.. .





17 o


„ „ inner ends, feet. .. .

20 6






Height of lift, feet. .. ... .

25 100

29.2 61.2





Velocity of wind at maximum efficiency, miles

per hour. ... .

4.3 7 o

5.8 6.5

6 o




Ratio of velocity of tips of vanes to velocity of wind

.93 '77







Revolutions of mill, per minute .

5 o 6.8

13.o 13'3





Actual horse-power. .. .


o18 o


0.011 0.025





In too average hours in a calm locality-

Quantity of water lifted, gallons per hour .

495 306

153 135





In too average hours in a windy locality-

Quantity of water lifted, gallons per hour .

816 629

287 271





I. Toowoomba; conical sail wheel with reefing vane. II. Stover; solid sai wheel with rudder; hand control.

III. Perkins; solid wheel, automatic rudder. IV. and V. Althouse; folding sail wheel, rudderless. VI. Carlyle; special type, automatic rudder.

Table IV. gives the horse-power which may be expected, according to Wolff, for an average of 8 hours per day for wheels of the American type.

Diameter of

Wheel in Feet.

Velocity of

Wind in Miles

per Hour.

Horse-power of


Revolutions of

Wheel per Minute.







O 12


























Further information will be found in Rankine, The Steam Engine and other Prime Movers; Weisbach, The Mechanics of Engineering; and Wolff, The Windmill as a Prime Mover. (W. C. U.)

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Simple English

[[File:|thumb|A Dutch tower windmill surrounded by tulips]]

A windmill is an engine that is powered by the wind to produce energy. Often they are in a large building like traditional post mills, smock mills and tower mills. The energy windmills produce can be used in many ways, traditionally for grinding grain or spices, pumping water, sawing wood or hammering seeds. Modern wind power machines are used for generating electricity and are more commonly called wind turbines.



Hero's wind-powered organ (reconstruction)

A windwheel that operated an organ was described as early as the 1st century AD by the Greek engineer Hero. That could have been the first machine in history that used wind power.[1] [2] Vertical axle windmills were used in eastern Persia (Sistan) by the 9th century AD as described by Muslim geographers.[3] Horizontal axle windmills of the type generally used today were invented in Northwestern Europe in the 1180s.[4]

Early history

The first windmills had long vertical shafts with rectangle shaped blades and appeared in Persia in the 9th century.[3] The authenticity of an earlier anecdote of a windmill involving the second caliph Umar (634-644 AD) is questioned on the grounds of being a 10th century amendment.[5] Made of six to twelve sails covered in reed matting or cloth, these windmills were used to grind corn or draw up water, they were quite different from the European versions. A similar type of vertical shaft windmill with rectangle blades, used for irrigation, can also be found in 13th century China.

Windmills in culture and literature

[[File:|thumb|left|A windmill in Seacroft, Leeds, UK converted to a hotel.]] Miguel de Cervantes' book Don Quixote de La Mancha, - which helped cement the modern Spanish language and is one of the greatest works of fiction ever published [6] - features an important scene in which Don Quixote attacks windmills that he believes to be violent giants. This gave worldwide fame to La Mancha and its windmills, and is the origin of the phrase "tilting at windmills", to describe an act of uselessness. The 'Moulin Rouge' translated directly in French to mean the 'Red Windmill'.


  1. A.G. Drachmann, "Heron's Windmill", Centaurus, 7 (1961), pp. 145-151
  2. Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995), pp.1-30 (10f.)
  3. 3.0 3.1 Ahmad al-Hassan, Donald Hill: Islamic Technology. An illustrated history, 1986, Cambridge University Press, p.54f. ISBN 0-521-42239-6
  4. Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995), pp.1-30 (18ff.)
  5. Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995), pp.1-30 (8)
  6. "BBC". 

Further reading

  • A.G. Drachmann: "Heron's Windmill," Centaurus, 7 (1961), pp. 145-151
  • Hugh Pembroke Vowles: "An Enquiry into Origins of the Windmill", Journal of the Newcomen Society, Vol. 11 (1930-31)

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