Doug;
Some of the locomotives built by SLM for Swiss Railways had a similiar setup. As you stated, they had two sets of cylinders; one to drive the wheels, another to drive the cog.
I believe the series Great Railway Journeys had a special on Meiringen Railway. It showed HG 3/3 0-6-0cog #1067 at work. Like the 0-10-0 cog in your picture, it has an unusually tall appearing valve chest that in fact contains a second pair of cylinders for the rack.
Both it and the diesel locomotive that replaced it uses regular traction for most of the journey. When it reaches the steeper portions of the railway the rack is engaged; the diesel does it on the fly; but I assume the steam engine was stopped and the rack engine is engaged. It is much slower running on the rack, but of course wheel traction alone would not work; hence the dual drive.
Both Esslingen and SLM built these "mixed drive" engines; E1060 (Esslingen 5316/1966) is/was still operational at Amberawa, Java, Indonesia
I believe most other rack engines such as the Mount Washington cog engines have the wheels and cogs mounted on the same axles.
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