... a single principle, that of Maupertuis, and later in another form as Hamilton's Principle of least action... Fermat's... principle..., which nowadays is usually called the principle of least action.... Huygens propounded an undulatory theory of light, while Newton, calling on an analogy with the material point dynamics that he created, developed a corpuscular theory, the so-called "emission theory", which enabled him even to explain, albeit with a contrived hypothesis, effects nowadays considered wave effects, (i.e., Newton's rings).