Our balloons, for example, used to give the alarm to our chasers on the field every time an enemy plane arose. They observed all the movements of trains, so that we were able to compile a schedule of all arrivals and departures of Austrian trains, a feat which greatly aided us in the correct concentration of our fire. The Drago balloons are also entrusted with the task of recording the aerial activities of the enemy. Every fifteen days, the observers in the balloons must record upon a special chart, the number of enemy planes and balloons which have passed over our lines, and indicate the exact line over which they passed. The study of these charts is extremely interesting. An attack is usually directed against the spot which has been most photographed, and over which the enemy planes have passed most frequently. Therefore, if a record of the enemy flights is kept, it is easy to deduct which points of our defense are most interesting to the enemy. A practical method of discovering secrets of the enemy is the interception of the radio-telegrams which the enemy stations exchange among themselves. These telegrams, however, are always in code, and it is very difficult to learn the key to the code. There are certain cryptographers, highly experienced, who spend the entire day trying to decipher the hissing sounds which are intercepted by our receiving stations. At times they succeed in unraveling a few threads, but often, the enemy, who knows the heavy penalties to be paid by not changing codes frequently, has changed the mode of the cipher just when our experts had begun to understand it. It is all a duel of wits, a complicated game of stratagems and deceits, in which the adversaries study each other vigilantly in an attempt to take such advantage of any slight slip as may afford the opportunity for the striking of a fatal blow. Another element of great importance are the intercepting telephone stations. Special detachments, highly trained and equipped with special devices, leave our trenches by night to lay telephone lines along the ground as near the enemy trenches as possible. Powerful microphones, capable of enlarging the smallest sound, receive the sound vibrations in their travel along the ground and transmit them to our lines where a person who knows German well, and all the languages and dialects spoken on the other side is delegated to listen day and night to such messages as are intercepted. But counter-schemes have been found even for this method of espionage.