was expected to return to the shaft to perform relighting, a round trip of up to a few miles. For men on piece work, this meant a loss of income (perhaps 10% of their day's pay), which men wished to avoid and thus took the risk. From the mid-century onwards, and particularly after the 1872 act, lamps had to have a lock mechanism which prevented the miner opening the lamp. Two schemes existed: either a special tool was required which kept at the pit head or else opening the lamp extinguished the flame. The latter mechanism can be seen in the Mueseler, Landau, and Yates lamps below. Such a lamp was known as a protector lamp, a term picked up and used as a company name. Only on the return to the bank could the lamp man open the lamp for refilling and service. Various different locking mechanisms were developed; miners tended to be ingenious in finding ways of circumventing them. A number of additional lamps were supposed to accompany each gang of men, but restricting the number was an obvious economy for the pit owners. The light given out by these lamps was poor (particularly the Davy where it passed through the gauze); indeed, in early lamps, worse than candles. The problem was not solved until the introduction of electric lighting around 1900 and the introduction of battery-powered helmet lamps in 1930. The poor light provided yet another reason for miners to try to circumvent the locks. Early lamps (the Davy, Geordie and Clanny) had the gauze exposed to air currents. It was quickly discovered that an air current could cause the flame to pass through the gauze. The flame playing directly on the gauze heats it faster than the heat can be conducted away, eventually igniting the gas outside the lamp. The following data is compiled from : Following accidents such as Wallsend (1818), Trimdon Grange (1882) and the Bedford Colliery Disaster (1886), lamps had to be shielded against such currents. In the case of the Davy, a "Tin-can Davy" was developed which had a metal cylinder with perforations at the bottom and a glass window for the light from the gauze. Clanny derived lamps had a metal shield (typically tinned iron) in the shape of a truncated cone, called a bonnet covering the gauze above the glass cylinder. The important principle is that no direct current of