The Fourth Order Fresnel Lens Seeing The Light

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Application

The Fourth Order lens was used in major harbor lights which lead the mariner into the channel at the entrance of a harbor mouth. It was also frequently used on rivers and in harbors to mark shoals and islands. This was by far the most commonly used lens on the Great Lakes. Three of the lights outfitted with this lens were Eagle Harbor, Crisp Point and Marquette Harbor.

Specifications
Lens height: 28.43"
Focal length:  9.8"
Weight of assembly:  440 to 660 lbs.
Relative brightness (over sixth order): 2.31x
Useful range:  Up to 15 nautical miles.
Number in US Lighthouses in 1884: 221
Number in US Lighthouses in 1922:  350
Oil consumption per hour 5.25 oz.

References

Annual Report of the Lighthouse Board
, 1884
The United States Lighthouse Service
, Dept of Commerce, 1915
Aids to Navigation Manual, US Coast Guard, 1945
Comparative Table of Lens Orders, Mabel A. Baiges, 1988
Letter from Al & Helen Gademsky, 07/02/01

Terry Pepper. This page updated 12/02/2007

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