It was the first autonomous volatile machine of antiquity. It consisted of a light but powerful shell that had the form of a pigeon and had internally the bladder of a big animal. The aerodynamic pigeon was placed with the opening of the bladder adapted to the utmost opening of a heated airtight boiler (or a powerful piston air-pump). When the pressure of the steam or air exceeded the mechanical resistance of the connection, the pigeon was launched and continued its flight for some hundreds of meters, with the help of the compressed air force coming out of the bladder, according to the principles of aerodynamics.