A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Sean C
Date: 2020 Jan 3, 21:45 -0800
I am told that it was not uncommon for instrument makers to sell their sextants to resellers who would then attach their own names to the instruments. However, I believe it is more likely that J. Sewill was the person who ordered the sextant and would be the end user.
And yes, there are collectors who would be interested in it. You have what appears to be a very nice example with all of the bits and pieces. If the mirrors, shades and telescopes are in as good a condition as the arc and box appear to be, you could get top dollar for this type of sextant. Of course ... top dollar is only what someone is willing to pay for it. But I would not be surprised if you sold it for U.S.$600 ( ≈ €540 or £460) or more.
In fact, if you could provide pictures of the condition of the mirrors, shades, telescopes and as many more detailed pictures of the arc, frame, etc. as possible - I might even make an offer. But in all honesty, I think your best bet is to list it on eBay.