ese have even invited officials to look at their sketch-books,
which, had they had any suspicion or any eyes in their heads, would
have revealed plans and armaments of their own fortresses interpolated
among the veins of the botanist's drawings of leaves or on the
butterflies' wings of the entomologist. Some examples of secret
sketches of fortresses which have been used with success are shown on
the following pages.

[Illustration: _This sketch of a butterfly contains the outline of a
fortress, and marks both the position and power of the guns. The marks
on the wings between the lines mean nothing, but those on the lines
show the nature and size of the guns, according to the keys below._]

[Illustration: The marks on the wings reveal the shape of the fortress
shown here and the size of the guns.

[Illustration: FORTRESS GUNS.]

[Illustration: FIELD GUNS.]

[Illustration: MACHINE GUNS.]

_The position of each gun is at the place inside the outline of the
fort on the butterfly where the line marked with the spot ends. The
head of the butterfly points towards the north._]

[Illustration: _A smart piece of spy-work. Veins on an ivy leaf
show the outline of the fort as seen looking west (Point of the leaf
indicates north.)_]

[Illustration: _Shows where big guns are mounted if a vein points to
them._]

[Illustration: _Shows "dead ground," where there is shelter from
fire._]

[Illustration: _Shows machine guns._]

[Illustration: _Here is another of the methods by which I concealed
the plans of the forts I made._

_First of all, I would sketch the plan as shown in the picture above
giving the strength and positions of the various guns as shown below:_

_A. Kaponiers with machine guns._
_B. 15 cm. gun cupola._
_C. 12 cm. guns cupolas._
_D. Q.-F. disappearing guns._
_E. Howitzer cupolas._
_F. Searchlight._]

[Illustration: _Having done this, I would consider the best method of
concealing my plans. In this case I decided to transform the sketch
into that of a stained glass window, and if you will carefully examine
the picture above you will see how successfully this has been done.
Certain of the decorations signify the sizes and positions of the guns.
These signs are given below, together with their meaning._]

[Illustration: 1. 15 _cm. gun._

2. _Howitzers._

3. _Q.-F. disappearing guns._

4. 12 _cm. guns._

5. _Machine guns._

6. _Searchlight._]

[Illustration]

CONCEALING