It was with this work that Kepler in 1604 made his public entry into the domain of the theory of light and optics and thus effectively created the conditions of a radical renovation that would determine the development of this branch of physics in the seventeenth century. Without suppressing the original, enigmatic title, it seemed important to orient the reader by adding an appropriate title and by giving all of the necessary explanations, even before entering into a detailed presentation - at once scholarly, technical and philosophical - of the work itself. Catherine Chevalley has first of all attempted to satisfy this series of requirements. We can only advise the reader to follow her in the progression leading to the French translation of Kepler's text.
As for the translation, Chevalley has specified the problems and nature of her task, and has thus made an important contribution to the methodology of returning to original sources. But Kepler's text is not only a Latin text of the late sixteenth century written by an author from the Germanic cultural sphere, it is a technical text in which numerous passages - notably Chapter IV - testify more to a pure and simple transcription of personal notes than to a patiently executed draft. Only a work of translation such as the one undertaken here can point out this state of affairs, and the translator, confronted with undeniable instances of Kepler's carelessness, had to resist the temptation of rewriting some hasty or allusive sentences. She has tried to conserve the style and flavor of the text by putting the corrections and indispensable explanations in the footnotes.