El artículo examina tres propuestas de explicación del fenómeno de refracción de la luz formuladas por los pensadores medievales Roger Bacon, John Pecham y Erazmus Ciolek Witelo. Se muestra, en el caso de Bacon, que la explicación estaba soportada en una metafísica de la propagación de los poderes causales y anidaba un conflicto insalvable. En el caso de Pecham se muestra un mayor compromiso con la necesidad de una ley cuantitativa que, desafortunadamente, conduce a una explicación frustrada. Finalmente, se valora (...) el deseo de Witelo por introducir elementos cosmológicos en su explicación. (shrink)

The idea that nature is governed by laws and that the goal of science is to discover and formulate these laws, rose to prominence during the Scientific Revolution of the seventeenth century. It was manifestly held by the most significant actors of that revolution such as Galileo, Descartes, Kepler, Boyle, and Newton. But this idea was not new. In fact, it made an appearance in the Middle Ages, and it is likely to have emerged already in Antiquity.1In this paper we (...) pay close attention to the concept of law of nature in the writings of Roger Bacon, the outspoken Franciscan who promoted experimental science. We will be using Bacon as a test case to show that long before the... (shrink)

At the beginning of the seventeenth century, the sine law of refraction had been discovered. Thus, natural philosophers tried even more to find a cause of refraction and to demonstrate the law. One of them was Thomas Hobbes, who was the author of the Leviathan and also worked on optics. At first, in the Hobbes analogy , he was influenced by Ibn al-Haytham, just as Descartes was in his famous proof in the Dioptrique . In his later optical scripts Tractatus (...) Opticus I , Tractatus Opticus II , and A Minute or First Draught of the Optiques , he developed a new explanation. Rejecting a corpuscular theory of light, Hobbes conceived a ray not as a body but as a motion originating from the light source: a ray can only be the motion of a body. The normal to the sides of a ray is called 'linea lucis'. If a ray is incident into another medium with a different density, one part of the linea lucis will be in the rarer and the other in the denser medium during an imperceptibly short period. Because the resistances in the two media are different, the parts of the linea lucis will move with different velocities; as a result the linea lucis will rotate and the direction of the ray will be changed. The next explanation given in De Corpore comes closer to the first one that Hobbes set down in the analogy. It must be asked why he replaced the theory of rotation by one which seems to carry less conviction. The reason could be that the dropped theory is founded in part on basic requirements of a corpuscular theory of light. Abandoning the whole theory might have been the lesser evil for Hobbes. In two later works, the Problemata Physica and the Decameron Physiologicum , Hobbes varied his explanation without giving any proof for the sine law. It should be noted, however, that in the Decameron he refers to the proof contained in the Tractatus Opticus I, but not that given in De Corpore. (shrink)

Snell's law of refraction did not affect the study of optics until twenty‐five years after its publication in 1637 and by then its universality threatened to break down already. Two optical phenomena—colour dispersion and strange refraction—were discovered that did not conform to the sine law. In the early 1670s, Isaac Newton and Christiaan Huygens respectively investigated these phenomena. They tried to describe the irregular behaviour of light rays mathematically and to reconcile it with ordinary refraction. This paper discusses their investigations (...) and aims at throwing new light on the history of seventeenth‐century optics. Both initially approached the problem in a mathematical way in which they built on Descartes' analysis of refraction. This is surprising because it contradicts their earlier dismissal of Descartes' account and it does not fit our picture of them as mathematical physicists. By looking more closely at their early investigations it becomes clear that Newton and Huygens first had to develop the approach to optics of their later writings. After Descartes placed the issue of the physical nature of light rays on the scientific agenda in 1637, they recognized its purport in their struggles with colour dispersion and strange refraction. It was at this point that their physical optics evolved from the traditional geometrical optics with which they had started. (shrink)