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The lantern house was surrounded a central bull's-eye lens with a series of concentric glass prismatic rings. By adding triangular prism sections above and below
the main lens, it steepened the angle of incidence at which rays shining up and down (lost light) could be collected and made to emerge horizontally. All the collected light emerged through the bull's-eye as a
narrow, horizontal pencil-like beam. This is known as the Fresnel catadioptric system. Fresnel designed different size apparatus for different requirements for different lighthouses. They were
designated First (1st) through Sixth (6th) Order and varied in size from 7 feet 10 inches (1st Order) down to 1 foot 5 inches (6th Order) inside diameter. Refer to our History page for additional information about
the Cape Meares first order Fresnel lens. |
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