Ostensive demonstration is that which concludes directly to that which is in question. Reduction ad impossibile is that which, when something the opp… - Robert Grosseteste

I hold that the first form of a body is the first corporeal mover. But this is light, which as it multiplies itself and expands without the body of matter moving with it, makes its passage instantaneously through the transparent medium and is not motion but a state of change. But, indeed, when light is expanding itself in different directions it is incorporated with matter, if the body of matter extends with it, and it makes a rarefaction or augmentation of matter; for when light is itself charged with the body of matter, it produces condensation or rarefaction. So when light generates itself in one direction drawing matter with it, it produces local motion; and when light within matter is sent out and what is outside is sent in, it produces qualitative change. From this it is clear that corporeal motion is a multiplicative power of light, and this is a corporeal and natural appetite.

This part of optics, when well understood, shows us how we may make things a very long distance off appear as if placed very close, and large near things appear very small, and how we may make small things placed at a distance appear any size we want, so that it may be possible for us to read the smallest letters at incredible distances, or to count sand, or seed, or any sort of minute objects.

The highest part of the human soul, which is called the intelligence and which is not the act of any body and does not need for its proper operation a corporeal instrument—this intelligence, if it were not obscured and weighed down by the mass of the body, would itself have complete knowledge from the irradiation received from the superior light without the help of sense, just as it will have when the soul is drawn forth from the body, and as perhaps those people have who are free from the love and the imaginings of corporeal things.