Safety lamp. A design for a miners' safety lamp by George Stephenson made in 1815. This was Stephenson's fourth design, intended to prevent explosions caused in coal mines by 'firedamp' (methane). The tin outer case is punctured with numerous holes to let light. Inside there is a glass bottle. Air enters the bottle through the tube at lower left and passes over a burning wick inside the bottle. Gases leave through a perforated metal disc in the top. This arrangement restricts the volume of oxygen that passes over the flame. If firedamp is in the air, the flame burns temporarily brighter, using up more oxygen and damping itself. This object is preserved at the Royal Institution, London.