And because this Experimental Science is wholly ignored by the general run of students, for that reason I can not convince people of its utility unle… - Roger Bacon

Prudens quaestio dimidium scientiae.

Everything in nature completes its action through its own force and species alone... as, for example, fire by its own force dries and consumes and does many things. Therefore vision must perform the act of seeing by its own force. But the act of seeing is the perception of a visible object at a distance, and therefore vision perceives what is visible by its own force multiplied to the object. Moreover, the species of the things of world are not fitted by nature to effect the complete act of vision at once, because of its nobleness. Hence these must be aided by the species of the eye, which travels in the locality of the visual pyramid, and changes the medium and ennobles it, and renders it analogous to vision, and so prepares the passage of the species itself of the visible object... Concerning the multiplication of this species, moreover, we are to understand that it lies in the same place as the species of the thing seen, between the sight and the thing seen, and takes place along the pyramid whose vertex is in the eye and base in the thing seen. And as the species of an object in the same medium travels in a straight path and is refracted in different ways when it meets a medium of another transparency, and is reflected when it meets the obstacles of a dense body; so is it also true of the species of vision that it travels altogether along the path of the species itself of the visible object.

I have labored much in sciences and languages, and I have up to now devoted forty years [to them] after I first learned the Alphabetum; and I was always studious. Apart from two of these forty years I was always [engaged] in study [or at a place of study], and I had many expenses just as others commonly have. Nevertheless, provided I had first composed a compendium, I am certain that within quarter or half a year I could directly teach a solicitous and confident person whatever I know of these sciences and languages. And it is known that no one worked in so many sciences and languages as I did, nor so much as I did. Indeed, when I was living in the other state of life [as a Magister], people marveled that I survived the abundance of my work. And still, I was just as involved in studies afterwards, as I had been before. But I did not work all that much, since in the pursuit of Wisdom this was not required.