THERE is a point in connection with the ordinary expositions of Fresnel's theory of double refraction to which, on account of its frequent occurrence, it is perhaps worth while to direct attention.

Making a glass Fresnel lens with its concentric rings requires even more work, but as the ever-resourceful [Robert Murray-Smith] shows us, a Fresnel lens can be made from far more mundane materials.

If you are a Hackaday reader, you probably know what a Fresnel lens is. You find them in everything from overhead projectors to VR headsets. While it seems commonplace now, the Fresnel lens was an ...