Caption:

Two early safety lamps. The carbon filament Swan lamp was introduced in 1878 and electric lamps were used for stationary purposes underground in Glasgow and Nottingham as early as 1881. The lamp shown on the left has a rheostat, which reduced the current consumption when only a dim light was required. Both have on-off switches and springs to keep the filament loops in contact. The space between outer casing and lamp bulb was made airtight, but with sufficient air to consume the filament if the bulb should break.