TO THE LOVER OF TRUTH, BROTHER WILLIAM OF MOERBEKE,

Witelo, son of Thuringians and Poles, wishes a happy intuition of the eternal light with an unrefracted ray of the mind, and a clear understanding of the things written below.

A large decorative drop-cap 'V' featuring a detailed woodcut scene of a landscape with rolling hills, a gabled building, and clouds in the sky.

The studious love of universal beings, holding you bound, has so joined me to you as one desiring the same thing, that your will is a command to me, and it also keeps me from the effects of those passions which are displeasing to you. Since, therefore, as a diligent searcher of all being, while you were joining the intelligible being—proceeding from its first principles—to individual sensible beings by way of cause through an act of the mind, and were investigating the individual causes of individual things, it occurred to you that the influence of divine virtues upon lower corporal things happens in a wonderful way through superior corporal virtues. For lower corporal things in the order of the parts of the universe are not partakers of divine virtue incorporeally, but they participate in a contracted virtue through the higher things of their order as far as they are able, just as in the other order of intellectual substances, you perceived with the sharpness of your mind that lower substances are made through the illumination of the higher of their order derived from the fountain of divine goodness, according to the nature of each, by way of intelligible influences. Thus, all the entity of things flows from the divine entity, and all intelligibility from the divine intelligence, and all vitality from the divine life; of which influences divine light is the principle, the medium, and the end in an intelligible way: as that from which, through which, and toward which all things are disposed.

But the sensible light of corporal influences is the medium connecting the superior bodies—which are perpetual in substance and exist only in potency regarding location—to the lowest bodies, which vary wonderfully according to forms and location, illuminating and connecting them. For light is the diffusion of the highest corporal forms, applying itself by the nature of corporal form to the matters of lower bodies, and impressing upon transitory bodies, in a divisible way, the forms of divine and individual craftsmen brought with it, and by its incorporation with them, always producing new specific or individual forms, in which there shines back, through the act of divine light, the craftsmanship of both the moved orbs and the moving powers. Because, therefore, light has the act of corporal form, it equals itself to the corporal dimensions of the bodies into which it flows, and extends itself with the extension of the capable bodies; yet because it always has the fountain from which it flows according to the beginning of its power, it takes on the dimension of distance, which is a straight line, as an accident, and thus fits to itself the name of "ray." And since a natural straight line is always in some natural surface, and the property of surfaces which happens to them through their bounding lines is an angle: therefore, angular consideration is adjacent to the luminous ray, and the perpendicularity of the rays is the cause for right angles. But the slant of the irradiating body over the irradiated body causes acute and obtuse angles, and they vary according to the influences of such luminaries. When, therefore, the skillful diligence of your genius saw fit to imitate the divine power of these celestial influences with respect to receptive things, and saw that things acted upon differ not only according to the active virtues but according to the diversity of the mode of action, it pleased you to be occupied in the hidden investigation of that matter, and to apply your studious soul to its diligent inquiry.

To you, therefore, searching the books of the ancients on this business, there occurred the boredom of Arabic verbosity, the complexity of the Greek, and also the scarcity of Latin writing, especially because the office of the Penitentiary of the Roman Church committed to you, a part of whose care you bear—believing that you should assist penitents more by the practical intellect than the speculative—restrained you from the multitude of things to be seen; for you preferred to assist the ailments of languishing souls with a divine antidote rather than to relieve the ignorance of those same men. And thinking me to be at leisure, you wished to bind me by the bond of love by which I am joined to you, so that I might undergo this burden of labor pleasing to you, and apply my mind to these matters not yet known to me. But I, who desire to obey all your commands, regarding your will as a mandate, have set aside for a time a chapter of a greater work which I had once undertaken to write concerning the order of beings, and the expense of the present work according to the strength of my ability, to which I confess myself unequal here, [I have added...]