Extraordinary refraction, 55, 56.
Fermat, principle of, 42.
Figures of transparent bodies, 105.
Hooke, Robert, 20.
Iceland Crystal, 2, 52 sqq.
Iceland Crystal, Cutting and Polishing of, 91, 92, 98.
Leibnitz, G.W., vi.
Light, nature of, 3.
Light, velocity of, 4, 15.
Molecular texture of bodies, 27, 95.
Newton, Sir Isaac, vi, 106.
Opacity, 34.
Ovals, Cartesian, 107, 113.
Pardies, Rev. Father, 20.
Rays, definition of, 38, 49.
Reflexion, 22.
Refraction, 28, 34.
Rock Crystal, 54, 57, 62, 95.
Romer, Olaf, v, 7.
Roughness of surfaces, 27.
94