Begin from the line _m f_ with the eye below; then go up and do the same with the line _n f_, then with the eye above and close to the 2 gauges on the ground look at _m n_; then as _c m_ is to _m n_ so will _n m_ be to _n s_. If _a n_ goes 3 times into _f b, m p_ will do the same into _p g_. Then go backwards so far as that _c d_ goes twice into _a n_ and _p g_ will be equal to _g h_. And _m p_ will go into _h p_ as often as _d c_ into _o p_. [Footnote: The first three lines are unfortunately very obscure.] 102. I GIVE THE DEGREES OF THE OBJECTS SEEN BY THE EYE AS THE MUSICIAN DOES THE NOTES HEARD BY THE EAR. Although the objects seen by the eye do, in fact, touch each other as they recede, I will nevertheless found my rule on spaces of 20 braccia each; as a musician does with notes, which, though they can be carried on one into the next, he divides into degrees from note to note calling them 1st, 2nd, 3rd, 4th, 5th; and has affixed a name to each degree in raising or lowering the voice. 103. PERSPECTIVE. Let _f_ be the level and distance of the eye; and _a_ the vertical plane, as high as a man; let _e_ be a man, then I say that on the plane this will be the distance from the plane to the 2nd man. 104. The differences in the diminution of objects of equal size in consequence of their various remoteness from the eye will bear among themselves the same proportions as those of the spaces between the eye and the different objects. Find out how much a man diminishes at a certain distance and what its length is; and then at twice that distance and at 3 times, and so make your general rule. 105. The eye cannot judge where an object high up ought to descend. 106. PERSPECTIVE. If two similar and equal objects are placed one beyond the other at a given distance the difference in their size will appear greater in proportion as they are nearer to the eye that sees them. And conversely there will seem to be less difference in their size in proportion as they are remote from the eve. This is proved by the proportions of their distances among themselves; for, if the first of these two objects were as far from the eye, as the 2nd from the first this would be called the second proportion: since, if the first is at 1 braccia from the eye and the 2nd at two braccia, two being twice as much as one, the first object will look twice as large as the second. But if you place the first at a hundred braccia from you and the second at a hundred and one, you will find that the first is only so much larger than the second as 100 is less than 101; and the converse is equally true. And again, the same thing is proved by the 4th of this book which shows that among objects that are equal, there is the same proportion in the diminution of the size as in the increase in the distance from the eye of the spectator. On natural perspective (107--109). 107. OF EQUAL OBJECTS THE MOST REMOTE LOOK THE SMALLEST.