, to
point of sight, and from each division on _SB_, such as 40, 80, &c.,
draw horizontals parallel to base. We thus obtain squares 40 feet wide,
beginning at base _AB_ and reaching as far as required. Note how the
height of the flagstaff, which is 140 feet high and 280 feet distant, is
obtained. So also any buildings or other objects can be measured, such
as those shown on the left of the picture.

[Illustration: Fig. 89.]

XXXVI

MEASURING SCALE ON GROUND

A simple and very old method of drawing buildings, &c., and giving them
their right width and height is by means of squares of a given size,
drawn on the ground.

[Illustration: Fig. 90.]

In the above sketch (Fig. 90) the squares on the ground represent 3 feet
each way, or one square yard. Taking this as our standard measure, we
find the door on the left is 10 feet high, that the archway at the end
is 21 feet high and 12 feet wide, and so on.

[Illustration: Fig. 91. Natural Perspective.]

[Illustration: Fig. 92. Honfleur.]

Fig. 91 is a sketch made at Sandwich, Kent, and shows a somewhat similar
subject to Fig. 84, but the irregularity and freedom of the perspective
gives it a charm far beyond the rigid precision of the other, while it
conforms to its main laws. This sketch, however, is the real artist's
perspective, or what we might term natural perspective.

XXXVII

APPLICATION OF THE REDUCED DISTANCE AND THE VANISHING SCALE TO DRAWING A
LIGHTHOUSE, &C.

[Above illustration:
Perspective of a lighthouse 135 feet high at 800 feet distance.]

[Illustration: Fig. 93. Key to Fig. 92, Honfleur.]

In the drawing of Honfleur (Fig. 92) we divide the base _AB_ as in the
previous figure, but the spaces measure 5 feet instead of 3 feet: so
that taking the 8th distance, the divisions on the vanishing line _BS_
measure 40 feet each, and at point _O_ we have 400 feet of distance, but
we require 800. So we again reduce the distance to a 16th. We thus
multiply the base by 16. Now let us take a base of 50 feet at _f_ and
draw line _fD_ to 16th distance; if we multiply 50 feet by 16 we obtain
the 800 feet required.

The height of the lighthouse is found by means of the vanishing scale,
which is 15 feet below and 15 feet above the horizon, or 30 feet from
the sea-level. At _L_ we raise a vertical _LM_, which shows the position
of the lighthouse. Then on that vertical measure the height required as
shown in the figure.

The 800 feet c