nts in connexion with the
measurements on the base line, and the upper measuring line _TPK_.

LXVI

HOW TO DRAW AN INTERIOR AT AN ANGLE

Here we make use of the same points as in a previous figure, with the
addition of the point _G_, which is the vanishing point of the diagonals
of the squares on the floor.

[Illustration: Fig. 128.]

From _A_ draw square _Abcd_, and produce its sides in all directions;
again from _A_, through the opposite angle of the square _C_, draw a
diagonal till it cuts the horizon at _G_. From _G_ draw diagonals
through _b_ and _d_, cutting the base at _o_, _o_, make spaces _o_, _o_,
equal to _Ao_ all along the base, and from them draw diagonals to _G_;
through the points where these diagonals intersect the vanishing lines
drawn in the direction of _Ab_, _dc_ and _Ad_, _bc_, draw lines to the
other vanishing point V1, thus completing the squares, and so cover
the floor with them; they will then serve to measure width of door,
windows, &c. Of course horizontal lines on wall 1 are drawn to V1, and
those on wall 2 to V2.

In order to see this drawing properly, the eye should be placed about
3 inches from it, and opposite the point of sight; it will then stand
out like a stereoscopic picture, and appear as actual space, but
otherwise the perspective seems deformed, and the angles exaggerated.
To make this drawing look right from a reasonable distance, the point of
distance should be at least twice as far off as it is here, and this
would mean altering all the other points and sending them a long way out
of the picture; this is why artists use those long strings referred to
above. I would however, advise them to make their perspective drawing on
a small scale, and then square it up to the size of the canvas.

LXVII

HOW TO CORRECT DISTORTED PERSPECTIVE BY DOUBLING THE LINE OF DISTANCE

Here we have the same interior as the foregoing, but drawn with double
the distance, so that the perspective is not so violent and the objects
are truer in proportion to each other.

[Illustration: Fig. 129.]

To redraw the whole figure double the size, including the station-point,
would require a very large diagram, that we could not get into this book
without a folding plate, but it comes to the same thing if we double the
distances between the various points. Thus, if from _S_ to _G_ in the
small diagram is 1 inch, in the larger one make it 2 inches. If from _S_
to M2 is 2 inches, in