What are the bellows on the organ?

There are four types of bellows:
1. Feeder bellows: These are much like the familiar fireplace bellows. They are used to "raise the wind" - create wind pressure. In pre-industrial times these were operated by human power, either manually, with the feet and in some cases, both. Occasionally animal power was used. "Mechanical blowing" came in in the mid to late 19th century. Steam engines, internal combustion engines and water pressure motors were used until being rendered obsolete by electric motors.
2. Reservoir bellows: These were often of considerable size and held a reserve of wind. They were necessary before the advent of mechanical blowing due to the relatively meager capacity of the blowing apparatus of the time.
3. Regulator bellows: Similar to reservoir bellows (and often incorrectly called reservoirs) but usually of smaller dimensions. Regulator bellows contain valves that enable them to perform the function of maintaining a constant wind pressure.
4. Concussion bellows: Often called "Winkers." Usually of small dimensions, they are used like a shock absorber to compensate for sudden, small drops caused by multiple notes being played simultaneously and / or aerodynamic resonances withing isolated parts of the wind system.