Pit pony lowering harness. Used to lower work ponies into mines.
https://s3-us-west-1.amazonaws.com/h.../pit_pony1.jpg
https://s3-us-west-1.amazonaws.com/h.../pit_pony2.jpg
More: https://en.wikipedia.org/wiki/Pit_pony
Previously:
https://www.homemadetools.net/forum/...256#post101112
https://www.homemadetools.net/forum/...854#post102669