A diminished object should be seen from the same distance, height
and direction as the point of sight of your eye, or else your
knowledge will produce no good effect.

And if you will not, or cannot, act on this principle--because as
the plane on which you paint is to be seen by several persons you
would need several points of sight which would make it look
discordant and wrong--place yourself at a distance of at least 10
times the size of the objects.

The lesser fault you can fall into then, will be that of
representing all the objects in the foreground of their proper size,
and on whichever side you are standing the objects thus seen will
diminish themselves while the spaces between them will have no
definite ratio. For, if you place yourself in the middle of a
straight row [of objects], and look at several columns arranged in a
line you will see, beyond a few columns separated by intervals, that
the columns touch; and beyond where they touch they cover each
other, till the last column projects but very little beyond the last
but one. Thus the spaces between the columns are by degrees entirely
lost. So, if your method of perspective is good, it will produce the
same effect; this effect results from standing near the line in
which the columns are placed. This method is not satisfactory unless
the objects seen are viewed from a small hole, in the middle of
which is your point of sight; but if you proceed thus your work will
be perfect and will deceive the beholder, who will see the columns
as they are here figured.

Here the eye is in the middle, at the point _a_ and near to the
columns.

[Footnote: The diagram which stands above this chapter in the
original with the note belonging to it: "a b _e la ripruova_" (_a b_
is the proof) has obviously no connection with the text. The second
sketch alone is reproduced and stands in the original between lines
22 and 23.]