Graham Reynolds, ‘The Later Paintings and Drawings of John Constable’, New Haven, London 1984, pp. 67-70, pls. 213-215.
Constable made a scientific study of cloud formations; he was determined to represent them accurately, and at the same time he saw that clouds could best express the mood of a landscape. ‘It will be difficult to name a class of landscape in which the sky is not the key note, the standard of scale and the chief organ of sentiment’.
It has been suggested that the reason for the wagon stopping at the ford was to allow the river water to cool the horses’ legs and to soak the wheels. In hot dry weather, the wooden wheels would shrink away from their metal rims. Wetting the wheels reduced the shrinkage and kept the outer metal band in place. 
Sold at the exhibition with three other Constables to the dealer John Arrowsmith, The Hay Wain was brought back to England by another dealer, D. T. White; he sold it to a Mr. Young who resided in Ryde on the Isle of Wight. It was there that the painting came to the attention of the collector Henry Vaughan and the painter Charles Robert Leslie.  On the death of his friend Mr. Young, Vaughan bought the painting from the former’s estate; in 1886 he presented it to the National Gallery in London, where it still hangs today.  In his will Vaughan bequeathed the full-scale oil sketch for The Hay Wain, made with a palette knife, to the South Kensington Museum (now the Victoria and Albert Museum). 
The Haywain itself was created by John Constable in 1821 at the height of his skills and experience. It is a crying shaming that he was to pass away at only 60, just 16 years after he produced The Haywain when surely any further years would likely have included many more classic British landscape paintings.
Haywain will always remain the best art work from Constable’s career and the best place to start for those looking to study and understand his techniques and achievements. Other titles such as Dedham Vale are equally skilled but have never managed to obtain the same level of exposure.
Although the painting evokes a Suffolk scene, it was created in the artist’s studio in London. Working from a number of open-air sketches made over several years, Constable then made a full-size preparatory oil sketch to establish the composition before painting the final picture.
The view is of the millpond at Flatford on the River Stour. Flatford Mill was a watermill for grinding corn, operated by the Constable family for nearly a hundred years. It still survives and is about a mile from Constable’s birthplace at East Bergholt, Suffolk. The house on the left also survives; in Constable’s time it was occupied by tenant farmer Willy Lott.
The different tones all complement each other and are repeated to add harmony to this piece: the blue of the pool is reflected in the sky and the red of the house is highlighted subtly in the trees and in the harness of the horse.
It may be that Constable did not paint images of these problems because he did not want to draw attention away from the natural landscape itself. In The Hay Wain the workers happily fit in with nature and live in harmony with the area.