ERWIN SCHRODINGER The fundamental idea of wave mechanics Nobel lecture december 12, 1933 On passing through an optical instrument, such as a telescope or a camera lens, a ray of light is subjec reflecting surface. The path of the rays can be constructed if we know the two simple laws which govern the changes in direction: the law of refrac- tion which was discovered by Snellius a few hundred years ago, and the law of reflection with which Archimedes was familiar more than 2,000 years ago As a simple example, Fig. 1 shows a ray A-B which is subjected to refraction at each of the four boundary surfaces of two lenses in accordance with th Fermat defined the total path of a ray of light from a much more general point of view. In different media, light propagates with different velocities, and the radiation path gives the appearance as if the light must arrive at its destination as quickly as possible. (Incidentally, it is permissible here to con- sider any two points along the ray as the starting- and end-points. )The least deviation from the path actually taken would mean a delay this is the fa mous Fermat principle of the shortest light time, which in a marvellous manner determines the entire fate of a ray of light by a single statement and also includes the more general case, when the nature of the medium varies not suddenly at individual surfaces, but gradually from place to place. The at penetrates into it from outside, the more slowly it progresses in an inc oht mosphere of the earth provides an example. The more deeply a ray of lig ingly denser air. Although the differences in the speed of propagation areERWIN SCHRÖDINGER The fundamental idea of wave mechanics Nobel Lecture, December 12, 1933 On passing through an optical instrument, such as a telescope or a camera lens, a ray of light is subjected to a change in direction at each refracting or reflecting surface. The path of the rays can be constructed if we know the two simple laws which govern the changes in direction: the law of refrac￾tion which was discovered by Snellius a few hundred years ago, and the law of reflection with which Archimedes was familiar more than 2,000 years ago. As a simple example, Fig. 1 shows a ray A-B which is subjected to refraction at each of the four boundary surfaces of two lenses in accordance with the law of Snellius. Fig. 1. Fermat defined the total path of a ray of light from a much more general point of view. In different media, light propagates with different velocities, and the radiation path gives the appearance as if the light must arrive at its destination as quickly as possible. (Incidentally, it is permissible here to con￾sider any two points along the ray as the starting- and end-points.) The least deviation from the path actually taken would mean a delay. This is the fa￾mous Fermat principle of the shortest light time, which in a marvellous manner determines the entire fate of a ray of light by a single statement and also includes the more general case, when the nature of the medium varies not suddenly at individual surfaces, but gradually from place to place. The at￾mosphere of the earth provides an example. The more deeply a ray of light penetrates into it from outside, the more slowly it progresses in an increas￾ingly denser air. Although the differences in the speed of propagation are