This is an interesting item. It's a hand site level surveying instrument. You look through it and can see a bubble from the spirit level on top. We've included a photo looking through it. This model was first patented by Keuffel and Esser in 1897, but we this one is from about 1921 based on a catalog we found (image included).
The front brass piece can be adjusted by sliding it back and forth, but I'm not very sure exactly the purpose in this. I would think it adjusted the angle to be measured, but the side doesn't have any markings that I would expect if that was the case.
It's made mostly of brass and glass with a black coating. I'm not sure if this was paint or some rubber based product. This is somewhat scuffed in spots, but is has a really cool look. If you want to decorate your home or office with surveyors tools, and have a small space to fill, this is perfect. The leather belt pouch is worn and has some other damage, but also has a cool look.
An interesting item to collect, display, or perhaps even use.