It's called a Dashpot or dashpot timer.

It's application here or purpose is usually to slow the return of the playfield shutter (the wood slide plate that allows balls in trap holes to drop down). This also allows certain reset functions to finish. It was one of those "standard" pieces of hardware in that era so they often exist even on games without the shutter wood.

As was already stated, the bell shaped wind up is the electrical timer to disconnect power (either dry cell or AC). Hopefully, long after the player has shot all their balls.