http://www.ebay.com/itm/1912-William-Ainsworth-Surveyors-Mining-Transit-Orig-Box-Rare-Denver-Maker-/351741014521?hash=item51e565f1f9:g:Z8kAAOSwzhVWtVZH&apos ;">1912 William Ainsworth Survey inst.
This link is to an ebay listing.
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Forked ore veins?
The only superior evidence is that which you haven't yet found.
The outside one allowed a look straight down or up. Very useful when surveying in a mine.
Well, you'll note it IS a mining transit. Think about what is unusual about mine surveying.
From the Internet:
Auxiliary Mining Scopes were developed for use when in locations or situations where the operator had to shoot a line where the plate would interfere with the work at hand. Think up or down mine shafts. They were mounted over or outside of the plate line so that the operator could be sighted in on one line and shoot another without having to re set his instrument.
DDSM
You only get one try instead of the usual two when performing a sunshot astronomical observation with this instrument...
I used to play in mines, as a kid. I have been lots of places. Unusual in mines... lots of things. I was born in Coarsegold Ca. Many abandoned mines around there. But, having two telescopes, seems redundant....