Uncle Mark is holding a brace; in turn, the brace is holding a Charles Irwin style bit, invented by William Dimmit in 1884 and improved by Irwin in 1887. By 1934 the Irwin patents had long since run their course.
The context in which Mark is using the brace lends some perspective to this business of collecting old tools. There are no motorized machines anywhere in sight. Mark is apparently repairing a horse-drawn farm implement. That's a buckboard in the background.
The brace (shown in the image below, scanned at maximum resolution and then reduced without losing any significant detail in order to reduce download time) is a well developed design, one we see nowadays at nearly every flea market.
The brace has seen heavy use - one of the ferrules that hold the wrist handle in place has become shifted towards the upper handle. The ferrules are too narrow for them to be affixed by set screws. Yet the plating is still intact and no rust stains mar the appearance of the tool. It appears to have a rosewood wrist handle, making it a quality product.
There seems to be a screw head at about 45 degrees on the ratchet selector sleeve.
For the time being, the maker and inventor of this brace remain undeciphered.