I believe this is a visibility meter made by the English firm W Ottway of Ealing, London. Founded around 1904, Ottway was primarily known for their telescopes, microscopes, and gun scopes. I don't know the manufacturing date for it, but Ottway was in Ealing around 1910-1950 and was absorbed into Hilger and Watts in 1963.

I believe the six metal objects on the left were holders for filters of varying optical density, numbered 1 through 12. I don't have the filters. The eyepiece opens so that the individual filters can be inserted. The visibility is determined by seeing which filter just allows observation of a standard luminosity light at a specified distance. The instrument itself is of metal construction and is about 5 inches long x 1.75 inches high.

If anyone can provide more information about this device, please email me.

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