How does a weathervane work? It has to rotate quite freely on a vertical shaft and it has to be perfectly balanced, but crucially it has to have an unequal surface area on the two sides divided by the shaft, the tail and the head.

This is traditionally achieved using an asymmetric, mainly two-dimensional, design created in metal, or another material with similar properties. The thickness of the material may vary to ensure the asymmetric design can balance correctly.

The wind forces the feature with the larger surface area round into its path, so that the arrow on the head points back in the direction from which the wind is blowing.

But as at Brixton Windmill, the design can also be very basic – it simply has to have an equal mass but unequal surface area on the two sides. And of course, it has to be located on the top of a tall structure, as far as possible from other buildings.

These days Brixton Windmill’s flour is milled using the modular mill installed by the Ashby family in 1902. It was powered by steam initially, then later by gas. Today it is powered by electricity, mostly generated from fossil fuels.

But renewable energy sources, such as the sun’s heat and windpower, are being introduced, and about 17% of UK electricity is now generated from windpower. Occasionally the sails at Brixton Windmill are freed to catch the wind again, and this involves first aligning the sweeps to the wind, using the little red weathervane as a guide.

Image: Urban 75

A recent addition to the Brixton skyline is the large heron weathervane created by artist Maggi Hambling, situated on top of the Prince of Wales pub/KFC, opposite the Town Hall.

At Lords cricket ground, there is a famous silhouette of Old Father Time removing the bales from the wicket.

On the spires or towers of many older churches you can see weathervanes with designs of cockerels. This is because in the 9th century AD there was a papal edict that every church in Christendom must have a weathervane with this design, as a reminder of Peter’s denial of Christ. Such ‘weathercocks’ were an important community facility in agricultural villages across Europe.

John Ashby’s windmill was built in 1816, halfway up the north-facing Brixton Hill. This was not an ideal location to catch the prevailing south-westerly winds. A windmill at the top of the hill, or even in central Streatham looking south-west towards Sutton, might have been more successful. But this would have been further from the customers of Ashby’s Mill, and a suitable piece of land might not have been available to purchase.

In the event, Brixton Windmill was only powered by wind up until 1862, after which the development of the surrounding area was sheltering the windmill from its vital power source and making it unviable, until steam power was introduced in 1902.