Hi Bernard, Frank, David, et al.... glad you find my site interesting. it's an entirely different area of glass, something we're usually familiar with but overlook. People here don't recognize insulators on the shelf, but take them outsite and point at a telephone/power pole and they get it. In the UK, porcelain was king so you'll not see any glass telegraph or telephone insulators; suspension insulators yes (Pilkington, EIV, Sediver, etc). Likewise a vault light in captivity draws a blank, but "remember those grids of square purple glass blocks set in downtown sidewalks" almost always rings a bell.
Bernard, back in the eBay saddle again, good. I have a hexagonal Hayward Bros. vault light wending its way from Canada right this minute, so yours will have a friend. Also have a St. Pancras light now, so the UK collection is starting to shape up (everything's up from NIL).
Re the thingy: the embossing is hand engraved in a typical save-effort sans-serif font, very much like insulators of the period. Yes, it's strange that a paperweight/magnifier would have the patent date on it, especially upside-down. I am assuming it's a US patent-- the form of the patent declaration is typical, and don't they say "Registered" in the UK? Of course there are other countries too, but it smells American to me. The original owner thought it was a paperweight, but then changed his mind when he got it. I thought it might be a vault light, so bought it from him. Seems we're both wrong, but it's an interesting piece nonetheless. Seems optical one way or another, but isn't designed to be attached easily, which is why I'm leaning toward desk magnifier.
I will go the library and use their fast connection to page through all 200+ patents of that date and see what I find. I did check the optics classes I could identify, but didn't find anything from the right time-period. When I win the lottery I will pay a big team to make a proper patent#/date/inventor/title index of the USPO, all N millions of them.
P.S. Chips in vault lights are not a problem, usually it's a dream to find any new pattern, even a specimen (Bernard's light is slobber-inducing to all 3 of us who collect them). I only have a dozen or so different kinds out of the hundreds patented. They are very rare and getting more so, since the old ones are just smashed when removed, not saved. They're usually set in steel and concrete, so removal is very difficult. In the UK you can find entire panels of the set-in-iron kind at architectural salvage places, but they typically want Â£500+ for them. (salvo.co.uk has some Haywards listed, and retrouvius.com has some unidentified types). The cost of shipping entire panels to the US would be just a bit stiff, alas.