If you are a Hackaday reader, you probably know what a Fresnel lens is. You find them ... reasons you can’t see them. A lighthouse often marked an important point that you either wanted to ...

and in 1871 a fog signal was installed at Pigeon Point. In 1872, the lighthouse was completed and first lit on Nov. 15 using a first-order Fresnel lens — which is made up of 1,008 prisms ...