A vintage (possibly antique, though we can't verify that) Permissible Flame oil lamp for mineshafts by Koehler Mfg. Co. out of Marlboro, Massachusetts. The upper part of it, which is mesh on other mining lamps, is instead a perforated cylinder. This was to test the air in mineshafts for methane gas, which could cause the mine to explode if ignited. The flame inside a mining lamp wouldn't be enough to light the methane on its own, and the Permissible Flame lamps allow enough outside air near the flame to check the amount of methane- if the flame began turning blue at the edges and closer towards the wick, it meant there was a high amount of methane in the mineshaft, which would tell miners whether or not they could have candles lit- hence, "Permissible Flame." This one's in great shape and is ready to serve as a collection piece or as a functioning lantern when you go camping!