Musicians need to practice, and for organists this historically presented a problem: someone had to be engaged to pump a bellows to provide air pressure. One solution was the pedal harpsichord, a practice instrument that didn't require an assistant.
When the electric fan came along, there was no longer a need for a bellows, much less a bellows pumper. Soon the expensive and cumbersome pedal harpsichord disappeared as well -- until a revival a half century or so ago. This once nearly extinct instrument will be featured in a couple of Bach trio sonatas this week.