ameter
varies in accordance with the angle of the square in which it is placed,
as in Fig. 181, _cc_ is the diameter of the circle and _ee_ the diameter
of the ellipse. In parallel perspective the diameter of the circle
always remains horizontal, although the long diameter of the ellipse
varies in inclination according to the distance it is from the point of
sight, as shown in Fig. 182, in which the third circle is much elongated
and distorted, owing to its being outside the angle of vision.

[Illustration: Fig. 181.]

[Illustration: Fig. 182.]

XCVII

HOW TO CORRECT DISPROPORTION IN THE WIDTH OF COLUMNS

[Transcriber's Note:
The column referred to as "1" in the text is marked "S" in both
Figures.]

The disproportion in the width of columns in Fig. 183 arises from the
point of distance being too near the point of sight, or, in other words,
taking too wide an angle of vision. It will be seen that column 3 is
much wider than column 1.

[Illustration: Fig. 183.]

[Illustration: Fig. 184.]

In our second figure (184) is shown how this defect is remedied, by
doubling the distance, or by counting the same distance as half, which
is easily effected by drawing the diagonal from _O_ to 1/2-D, instead
of from _A_, as in the other figure, _O_ being at half base. Here the
squares lie much more level, and the columns are nearly the same width,
showing the advantage of a long distance.

XCVIII

HOW TO DRAW A CIRCLE OVER A CIRCLE OR A CYLINDER

First construct square and circle _ABE_, then draw square _CDF_ with its
diagonals. Then find the various points _O_, and from these raise
perpendiculars to meet the diagonals of the upper square at points _P_,
which, with the other points will be sufficient guides to draw the
circle required. This can be applied to towers, columns, &c. The size of
the circles can be varied so that the upper portion of a cylinder or
column shall be smaller than the lower.

[Illustration: Fig. 185.]

XCIX

TO DRAW A CIRCLE BELOW A GIVEN CIRCLE

Construct the upper square and circle as before, then by means of the
vanishing scale _POV_, which should be made the depth required, drop
perpendiculars from the various points marked _O_, obtained by the
diagonals, making them the right depth by referring them to the
vanishing scale, as shown in this figure. This can be used for drawing
garden fountains, basins, and various architectural objects.

[Illustr