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Chuck V
Looking at the link again https://www.rmg.co.uk/collections/objects/rmgc-object-43426 , you can see from the view in the box that both horizontal mirrors are half silvered as one might expect.  Also, both are fixed to the frame, so I don’t see how light from the lower mirror can possibly be seen through the telescope unless the telescope is free to swivel.  Is that what you’re assuming?  I’d discounted that possibility, but looking again at the rear view and the in-box view it is just possible that the telescope swivels about the axis of its holder.   This would make sense, but even so, using the law of reflection that states that the angle measured is twice the angle between the mirrors, I think I’ll stick with my statements a. and b for the moment.  DaveP