Augustin Fresnel forever,

at least for more than one century…
The coast line is very rugged and often in fog. So by the end of the 19th century lighthouses were set up all along the coast. There is one every 40 miles, each has a singular lightening pattern for recognition. Most of them are still in use. Nowadays the big container ships do not come so close to the shore that they could wreck but for the small local boats the light houses still serve for orientation. They are centrally administered and now guards live there anymore, but they still operate the old Fresnel lenses. These things are incredible. They were commissioned in Paris or England at time and shipped over, they consist of a number of glass laminates that focus the light of a very dim light source (still it us a simple light bulb as you have it in your home) such that it can be seen from 20 miles. The entire lense is egg shaped and turns to make the light blink, if it stopped turning you would have to switch off the light immedistely or else draw a curtain because it could cause forest fires at the point where the lightcone points to. So at least it was explained to me at the lighthouse on Cape Blanco where I finally managed to visit one of them.

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