New eBay listing
http://www.ebay.com/itm/VINTAGE-BRANDIS-SONS-NAUTICAL-SEXTANT-Original-Box-Amazing-L-K-/191524090278?ssPageName=ADME:SS:SS:US:3160Looks to me like the serial number is on the right end of the arc and it indicated NO 2539. Typically the Brandis numbers are 4 digits at the left end of the arc.
And it has a hand etched number on the frame of 161-U(?)SN-252222. Usually the USN number is hand etched at the middle of the arc.
This one is interesting. It is an F.E. Brandis, Sons & Co, Brooklyn NY unit, which would seem to pre-date the Brandis & Sons Mfgr Co. Here is a quick history from the Smithsonian site:
http://amhistory.si.edu/surveying/maker.cfm?makerid=5Frederick Ernest Brandis (1845–1916) was born in Germany, came to the United States in 1858, worked for Stackpole & Brother for a few years, and then opened his own instrument shop in 1871. The firm became F. Brandis & Co. in 1875, F. E. Brandis, Sons & Co. in 1890, and Brandis & Sons Mfg. Co. in 1916. The Pioneer Instrument Company purchased control of Brandis in 1922, and sold it to the Bendix Aviation Corporation in 1928. The manufacture of Brandis instruments ceased in 1932.
So, it would seem that this unit had to be manufactured between 1890 and 1916. Perhaps it pre-dates most of the sextants we've seen, hence the unusual placement of the serial number.
I've asked the seller if there are any other numbers on the instrument or the box.
Andrew