April 23rd, 2012 by Bruce Coast Lighthouse Admin
The main feature of the Ghostly Guardians Exhibit at the Bruce County Museum & Cultural Centre is the Fresnel lens.
The lens is from the Cape Croker Lighthouse, which is on temporary loan from The Canadian Coast Guard in agreement with The Chippewas of Nawash – Unceded First Nation. It was removed in 2007, from the reinforced concrete octagonal tower, the first of its kind on Georgian Bay.
The Fresnel lens is one of two types of lenses used in lighthouses. Augustin Fresnel invented the Dioptric lens in 1823 and it is now named for him. The lenses work on the principal of the refraction of light through lenses and prisms (glass), on to the desired focal plane, by a central light source. Dioptric system lights are categorized in a descending rank of brilliancy. 1st Class being the most powerful to 7th Class.
Fresnel lenses from the Louis Sautter Company of Paris adorned the Point Clark, Chantry Island, and Cove Island lighthouses. All boasted a 2nd order lens. Cape Croker held a 3rd order lens, while Big Tub and Flower Pot Island were 7th order.