The extraordinary ingenuity shown by spies in securing the plans of other countries' fortifications has been amply illustrated in the war, although, of course, we know but a little part of what the spies have accomplished.
A woman was caught at the French frontier seeking to enter Switzerland and presumably intending to return to Germany or Austria. She was thoroughly searched by a matron, as is customary in such cases, but nothing was found.
Certain actions of hers, however, had given rise to serious suspicions, and one of the cleverest officers of the French Secret Service was detailed to examine her. He applied several tests to her. He finally obtained what he wanted by seating her, in an undraped condition, tied to a chair, before a warm fire.
"Brutes, you are going to burn me alive!" she shrieked as she was forced into a chair.
"Be calm, madame," said the officer. "We only want to admire your beautiful back."
There appeared on the ample back of this fair-haired lady an elaborate design. To the experienced eye of the officer it represented a plan of one of the most important French fortresses. The number of guns, their sizes and positions were shown. The angles, sallies and extent of the fortifications were clearly indicated. The weak spots in the defense were made clear. This fortress had been entirely made over since the outbreak of the war, and it was of vital importance to the Germans to know its present arrangements.
A German spy in France, evidently a man with military knowledge, had obtained access to the fortress, but there was but slight chance of his getting home with his knowledge. He had, therefore, used the young woman as an innocent looking agent.
The master spy had traced the plans on her back with sulphate of copper. This liquid leaves no mark on the skin under normal conditions, but when exposed to considerable heat it shows up dark blue. For further secrecy, it is stated, the plan of the fortress was concealed within another design in the manner described by General Sir Robert Baden-Powell. He carried with him an illustrated book on butterflies and from this he made what would appear to be specimens of butterflies seen in the surrounding country. Then when he had obtained the details of a fortress he drew them in among the complicated markings on the wings of the butterfly. There they would escape notice by any but the most expert "spy trappers."
Miss Sari Petrass, the beautiful Hungarian dancer, who was for some time a great favorite in London, is reported to have been shot in Budapest as a spy. She is supposed to have been engaged in gathering military information in her native country for the benefit of England, where she made her greatest artistic success.