<P> His more general consideration of light as a primary agent of physical causation appears in his On Lines, Angles, and Figures where he asserts that "a natural agent propagates its power from itself to the recipient" and in On the Nature of Places where he notes that "every natural action is varied in strength and weakness through variation of lines, angles and figures ." </P> <P> The English Franciscan, Roger Bacon (c. 1214--1294) was strongly influenced by Grosseteste's writings on the importance of light . In his optical writings (the Perspectiva, the De multiplicatione specierum, and the De speculis comburentibus) he cited a wide range of recently translated optical and philosophical works, including those of Alhacen, Aristotle, Avicenna, Averroes, Euclid, al - Kindi, Ptolemy, Tideus, and Constantine the African . Although he was not a slavish imitator, he drew his mathematical analysis of light and vision from the writings of the Arabic writer, Alhacen . But he added to this the Neoplatonic concept, perhaps drawn from Grosseteste, that every object radiates a power (species) by which it acts upon nearby objects suited to receive those species . Note that Bacon's optical use of the term "species" differs significantly from the genus / species categories found in Aristotelian philosophy . </P> <P> Another English Franciscan, John Pecham (died 1292) built on the work of Bacon, Grosseteste, and a diverse range of earlier writers to produce what became the most widely used textbook on Optics of the Middle Ages, the Perspectiva communis . His book centered on the question of vision, on how we see, rather than on the nature of light and color . Pecham followed the model set forth by Alhacen, but interpreted Alhacen's ideas in the manner of Roger Bacon . </P> <P> Like his predecessors, Witelo (c. 1230--1280 x 1314) drew on the extensive body of optical works recently translated from Greek and Arabic to produce a massive presentation of the subject entitled the Perspectiva . His theory of vision follows Alhacen and he does not consider Bacon's concept of species, although passages in his work demonstrate that he was influenced by Bacon's ideas . Judging from the number of surviving manuscripts, his work was not as influential as those of Pecham and Bacon, yet his importance, and that of Pecham, grew with the invention of printing . </P>

What technological breakthrough did the mesoptamians make in agriculture