Ruskin, John; Cook, Edward T. [Hrsg.]: The works of John Ruskin: The elements of drawing. The elements of perspective. And the laws of Fésole (London, 1904)

INTRODUCTION

WHEN you begin to read this book, sit down very near
the window, and shut the window. I hope the view out
of it is pretty; but, whatever the view may be, we shall
hnd enough in it for an illustration of the first principles
of perspective (or, literally, of "looking through ').
Every pane of your window may be considered, if you
choose, as a glass picture; and what you see through it, as
painted on its surface.
And if, holding your head still, you extend your hand
to the glass, you may, with a brush full of any thick colour,
trace, roughly, the lines of the landscape on the glass.
But, to do this, you must hold your head very still.
Not only you must not move it sideways, nor up and down,
but it must not even move backwards or forwards ; for, if
you move your head forwards, you will see of the
landscape through the pane; and, if you move it backwards,
you will see or considering the pane of glass as a pic-
ture, when you hold your head near it, the objects are
painted small, and a great many of them go into a little
space; but, when you hold your head some distance back,
the objects are painted larger upon the pane, and fewer of
them go into the held of it.
But, besides holding your head still, you must, when
you try to trace the picture on the glass, shut one of
your eyes. If you do not, the point of the brush appears
double; and, on farther experiment, you will observe that
each of your eyes sees the object in a different place on
the glass, so that the tracing which is true to the sight of
the right eye is a couple of inches (or more, according to
XV. 241 a