Here is a lovely piece of mechanical folk now housed at the American Folk Art Museum. The piece has a remarkable history. It probably dates to around 1875. At some point in the early twentieth century, it was stashed inside the plaster wall of a house. When the house was renovated years later, the piece was rediscovered. Some unknown person left a little treasure for later generations! Thank you whoever you are.
More about the knife-grinder:
Knife grinders such as the gentleman depicted here were a common sight in urban areas and larger towns in the nineteenth century, at a time when tradesmen and vendors plied the streets in search of business. By mounting a grinding stone on a handmade cart, knife grinders could offer a convenient service to customers, particularly in residential neighborhoods where the periodic sharpening of blades used in the home and garden was best accomplished on a large wheel.
The large wheel has a number of interior vanes that allowed the wind to power the piece, moving the man's leg as if he were treading the wheel to sharpen the knife.
Here is where you can learn more about the knife-grinder whirligig.[ Thanks Eric! ]