Treatise on light : $b In which are explained the causes of that which occurs in reflexion, & in refraction and particularly in the strange refraction of Iceland crystal

"Treatise on Light" by Christiaan Huygens is a scientific treatise written in the late 17th century. The work delves into the properties of light, focusing on phenomena like reflection and refraction, and makes significant observations about the unusual behavior of Iceland crystal. Huygens aims to rationalize the behavior of light through principles drawn from both mathematics and experimental evidence, offering explanations that reflect the scientific inquiries of his time. The opening of the treatise introduces the author’s motivation for writing and the context in which his findings were presented, specifically to the Royal Academy of Science in France. Huygens describes the foundation of his work as based on both logical deductions and empirical observations, expressing a desire to clarify misconceptions about light propagation. He discusses the perception of light as a movement of ethereal matter, critiques previous theories, and lays the groundwork for exploring the principles of light's straight-line propagation, reflection, and refraction, ultimately leading to a detailed investigation of the unique properties observed in Iceland crystal. The discussion sets the stage for the treatise's exploration of optical phenomena and the pursuit of scientific truth.