I hope this is not too off topic I but found it fascinating. I had the good fortune to ride in the cab of the Baldwin Steam locamotive operated by the Tenn Valley Rail Road Musium two years ago and the engineer was explaining to me what he was doing as he operated the engine. There are two main levers that control forward motion. The first is the throttle that controls the amount of steam to the cylinders. The second basically does the same thing the transmission does in an automobile and has the effect of changing gears. This provides more torque at start up and more speed with less steem when cruising.
Question. How is this accomplished?