English: Cutaway drawing of a lighthouse lantern room from mid 1800s showing the Fresnel lens. Source says this was a lens of the 'largest size', made by M. Souter and exhibited at the Paris Universal Exposition in 1855. The cylindrical lens with 8 faces stood 10 feet high. A clockwork mechanism (M), driven by weight (P), slowly turns the entire lamp-lens assembly (A,B) on six rollers. This system, invented by Augustin-Jean Fresnel, scans the 8 beams from the lens around the whole horizon. The resulting regularly flashing light seen by mariners served to distinguish the lighthouse from stars or shore lights. Alterations: removed caption.