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Brixton Windmill

Image: Owen Llewellyn

The millís construction

Brixton Windmill is a tower mill – a design that was first introduced in the late 13th century. The advantage of a tower mill over the earlier post mill was that it was not necessary to turn the whole body of the mill with all its machinery into the wind.

The windmill is 15 metres (49.5 feet) high and is arranged over five storeys – a modest size compared with England’s tallest tower mill at Moulton in Lincolnshire, which is nine storeys and 30 metres high. The base of Brixton Windmill is 6.6 metres (22 feet) in diameter and 3.65 metres (12 feet) at the top.

Brixton Windmill has four sails, or sweeps, but some millwrights on other mills experimented with more sails to increase efficiency. Some tower mills have six or even eight sails to increase the surface area that catches the wind.

Generally, tower mills were more powerful than watermills but less reliable due to the unpredictable nature of the wind. 

Windmill cap

Image: Owen Llewellyn

The cap

The cap (at the top) is an attractive boat-shaped structure – timber framed and weatherboarded.

The cap can be turned using a chain arrangement; you can see the wheel of this chain system at the back of the cap. 

Brixton Windmill

Image: Owen Llewellyn

The sails

South of the River Thames sails were traditionally called ‘sweeps’. The original sails were removed and burnt in 1864. The design of the newly restored sails was based on old photographs of Ashby’s Mill showing two different pairs of sails – common sails and patent sails.

The trellis-like common sail was the standard sail in the 18th century. Canvas sailcloth was laid along each sail frame. In light winds the whole canvas would be unfurled; in stronger winds the sails would be ‘reefed’, or rolled back, so that only a part of the surface was exposed.

The common sail was light, simple, inexpensive and fairly efficient, so its use continued well into the 20th century. However, to adjust them from the ground, each sail had to be stopped in turn in a vertical position. So with four sails, the rotation had to be stopped four times. 

The invention of patent sails in 1807, by William Cubitt, eliminated this problem. Patent sails are made up of shutters that can be opened and closed on the same principle as a Venetian blind. This design provided a system for automatically changing the amount of sail exposed as the strength of the wind varied. This saved time and meant that the miller could produce more flour.

Here is an extract from an advertisement of Cubitt’s patent in the Norfolk Chronicle on the 13 June 1807:

"CUBITT’s new invented SAILS or VANES for WINDMILLS will preserve an even and uniform velocity in the most unsteady wind and will clothe and unclothe themselves by the wind’s impulse (without altering their angle of weather) whether they be in motion or at rest; by which means they are rendered perfectly safe in any gale of wind, however sudden and strong it may be. These vanes will be found to be a very valuable acquisition to every one whose interest consists in having their Mills make the most possible of weak winds and never exceed a proper velocity in the strongest; they are easily applicable either to Post or Tower Mills, are very simple and durable in their construction and not in the least liable to be out of order. They will be found extremely useful in draining of marshes as they may be left to work night and day, perfectly safe without any person attending them."

There was probably a stage – a gallery or platform – running round the outside of Brixton Windmill to let the miller reach the sails and haul the canvas onto them. At the first floor level there are two doors which would have given access to this gallery.