PART FIVE OF THIS PLEA

CONCERNING OPTICS, IN THREE PARTS

The first part treats of matters common to the other two; the second deals mainly with direct vision; the third with reflected and refracted vision. In Part One there are twelve distinctions.

FIRST DISTINCTION

This distinction deals with the properties of this science, with the parts of the mind and brain, and with the organ of vision, in five chapters.

CHAPTER I

Concerning the properties of this science.

Having explained the fundamental principles of wisdom—both sacred and human—found in the languages from which the sciences of the Latins have been translated, and likewise in mathematics, I now wish to discuss some principles that belong to optics. If the study just mentioned is noble and pleasing, the one in hand is far nobler and more pleasing. This is because we take special delight in vision; light and color possess a particular beauty surpassing the other things brought to our senses. Not only does beauty shine forth, but advantage and a greater necessity appear as well.

For Aristotle says in the first book of the Metaphysics that vision alone reveals the differences of things; by means of it, we search out experimental knowledge of all things in the heavens and on the earth. Those things located in the heavenly bodies are studied by visual instruments, as Ptolemy and other astronomers teach. The same applies to phenomena generated in the air, such as comets, rainbows, and similar things. Their altitude above the horizon, their size, form, number, and all other characteristics are verified by methods of viewing them through instruments. Our experience of things here on earth we owe to vision, because a blind man can have no experience worthy of the name concerning this