It used to amuse some of us to watch the foreign spies at work on our ground.  One especially interested me, who set himself up ostensibly as a coal merchant, but never dealt in a single ounce of coal.  His daily reconnaissance of the country, his noting of the roads, and his other movements entailed in preparing his reports, were all watched and recorded.  His letters were opened in the post, sealed up, and sent on.  His friends were observed and shadowed on arriving—­as they did—­at Hull instead of in London.  And all the time he was plodding along, wasting his time, quite innocent of the fact that he was being watched, and was incidentally giving us a fine amount of information.

Another came only for a few hours, and was away again before we could collar him; but, knowing his moves, and what photographs he had taken, I was able to write to him, and tell him that had I known beforehand that he wished to photograph these places, I could have supplied him with some ready made, as the forts which they recorded were now obsolete.

On the other hand, the exceedingly stupid Englishmen who wandered about foreign countries sketching cathedrals, or catching butterflies, or fishing for trout, were merely laughed at as harmless lunatics.  These 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: