It must have been an impressive sight for friend or foe to witness the departure of each aerial vessel on its venturesome mission. The bold plunge into space above the roofs of the imprisoned city; the rapid climb into the sky and, later, the pearl drop high in air floating away to its uncertain and hazardous haven, running the gauntlet of the enemy's fire by day or braving what at first appeared to be equal danger, attending the darkness of night. It will be seen, however, that, of the two evils, that of the darkness was considered the less, even though, with strange and unreasonable excess of caution, the aeronauts would not suffer the use of the perfectly safe and almost indispensable Davy lamp.

Before any free ascents were ventured on, two old balloons were put to some practical trial as stationary observatories. One of these was moored at Montmartre, the other at Mont-souris. From these centres daily, when the weather permitted, captive ascents were made--four by day and two by night--to watch and locate the movements of the enemy. The system, as far as it went, was well planned. It was safe, and, to favour expedition, messages were written in the car of the balloon and slid down the cable to the attendants below. The net result, however, from a strategic point of view, does not appear to have been of great value.