Mural painted by Alfred R Thomson RA in 1964. This scene shows the huge individually built combine harvesters or 'headers' used on the great wheat belts of California and the mid-west American states in the late 19th century. Up to 40 horses or mules were required to pull such machines. Power for both the cutting mechanism and the threshing head was derived from the machine's ground-wheels and, in soft conditions, chains would be placed around the wheels in order to increase the tractive effort.
© Science Museum / Science & Society Picture Library