perforated metal tube, to surround and protect the glass. Air intake was via an annular chamber around the base of the lamp (instead of previous tubes) into which air entered through small (") holes then passed through gauze into the lamp. If the glass surrounding the lamp was broken, the Geordie became a Davy. A strong enough current of air could travel through the tubes (later holes and gallery) and enlarge the flame, eventually leading to it becoming red-hot. The lamp becomes unsafe in a current of from 8 to 12 feet per second, about twice that of the Davy. Purdy lamp A development of the Geordie lamp was the Purdy. A galley with gauze provided the inlet, above the glass was a chimney with perforated copper cap and gauze outer. A brass tube protected the upper works, shielded them and kept them locked in position. A sprung pin locked the whole together. The pin could only be released by applying a vacuum to a captive hollow screw; not something that a nicotine starved miner could do at the coal face . Improved Clanny lamp Clanny abandoned his pumps and candles and developed a safety lamp which combined features of both the Davy and Geordie. The oil lamp was surrounded by a glass chimney with no ventilation from below. Above the chimney is a gauze cylinder with a double top. Air enters from the side and spent gases exit from the top. In the presence of firedamp the flame intensifies. The flame must be kept fairly high in normal use, a small flame permits the enclosed space to fill with firedamp/air mixture and the subsequent detonation may pass through the gauze. A larger flame will keep the upper part full of burnt gas. The Clanny gives more light than the Davy and can be carried more easily in a draught. Lupton notes however it is superior in no other respect, particularly as a test instrument. The glass on a Clanny was secured by a large diameter brass ring which could be hard to tighten securely. If a splinter occurred at the end of a crack, or indeed any other unevenness, then the seal might be compromised. Such an incident occurred at Nicholson Pit in 1856 on a lamp being used by an overman to test for firedamp. The mines inspector recommended that only Stephenson lamps were used for illumination and