in the arrangement of the _libro di pittura_ which is here presented
to the reader. They are however but few.]. But its axioms being laid
down at great length, I shall abridge them to a conclusive brevity,
arranging them on the method both of their natural order and of
mathematical demonstration; sometimes by deduction of the effects
from the causes, and sometimes arguing the causes from the effects;
adding also to my own conclusions some which, though not included in
them, may nevertheless be inferred from them. Thus, if the Lord--who
is the light of all things--vouchsafe to enlighten me, I will treat
of Light; wherefore I will divide the present work into 3 Parts
[Footnote: 10. In the middle ages--for instance, by ROGER BACON, by
VITELLONE, with whose works Leonardo was certainly familiar, and by
all the writers of the Renaissance Perspective and Optics were not
regarded as distinct sciences. Perspective, indeed, is in its widest
application the science of seeing. Although to Leonardo the two
sciences were clearly separate, it is not so as to their names; thus
we find axioms in Optics under the heading Perspective. According to
this arrangement of the materials for the theoretical portion of the
_libro di pittura_ propositions in Perspective and in Optics stand
side by side or occur alternately. Although this particular chapter
deals only with Optics, it is not improbable that the words _partiro
la presente opera in 3 parti_ may refer to the same division into
three sections which is spoken of in chapters 14 to 17.].

The plan of the book on Painting (14--17).

14.

ON THE THREE BRANCHES OF PERSPECTIVE.