Within days of the beginning of the siege, the director general of the Posts established the Balloon Post, designed to carry the mails out of Paris. The balloons themselves were filled with coal gas and were fitted with a gondola basket that carried the pilot and occasional passengers. In addition to the bags of mail, the balloons usually carried an allotment of homing pigeons, which were used to send microfilm messages back into Paris. In all, sixty-seven different balloons ascended from Paris during the siege, fifty-five of which were authorized by the Post to carry mails. Since the balloon voyages were at the mercy of the prevailing winds, the pilots had little control over the direction of the flights, and only moderate control over the duration and the actual landing area. Some balloons traveled only a few kilometers from Paris; others traveled great distances (one balloon landed in Norway). In general, the Paris Balloon Post was very successful, transporting more than 11,000 KG of mail out of Paris during the hundred twenty-eight day Siege.
In addition to the use of homing pigeons to send messages into Paris during the siege, attempts were made to place letters into zinc balls, which were then floated down the Seine River from Moulins. Within Paris a series of nets were erected to trap the zinc balls. This 'Boules de Moulins' service began on January 4, 1871, but was not successful as no zinc balls were ever recovered during the period of the Siege. Examples of these balls were retrieved later (some as late as 1982), from which the known letters survived.
Chaintrier, L. Balloon Post of the Siege of Paris, 1870-71. American Airmail Society, 1976.
Yvert and Tellier. Catalogue Spécialisé des Timbres de France. Vol. 1. 1975.
Heyd, G. Die Ballons von Paris 1870-71. December 1970.
Kremer, B. French Philatelic Facts. Vol. 3. No. 2. June 1951.