Balloon Mail 
In the Franco-Prussian War of 1870, the Germans encircled Paris, cutting off all communications with the rest of France – or so they thought. The French developed two ways to evade the blockade.
The first was to seal the outgoing mail in metal containers known as Boules de Moulins, in and float them down the Seine to be retrieved by the French Army. These provided target practice for the Germans in trying to sink them, but some made the passage successfully.
The second way around (or rather over) was by gas filled balloons which would float over the German line and land in friendly territory. This was more successful, but these were “free balloons” which were not controlled by the pilot. Normally, the pilot could only release gas to descend. The distance and direction depended on the wind. One balloon went as far as Norway/ But what does this have to do with Irish philately? Simple – 36 letters are known to exist addressed to Ireland. They were sent by British citizens trapped in Paris communicating to their families and business partners.
Figure 1 is a scan of a cover addressed to Co. Wicklow. This was in an article appearing in O.E.78 , the journal of the now defunct Irish Airmail Society. This particular flight was the balloon Lavoiser which was posted in Paris on19 December 1870. It flew on the 22nd and arrived in La Meenitre on the same day. It was forwarded to Newtown Mt Kennedy, Co. Wicklow on 26 December.(extracted from O.E.78 Vol. 6 No. 1, October 2001).
O.E.78 Vol. 6, No.1, Oct.2001 “Additional Balloon Montes” by Bill Murphy.
Articles in Irish Philately:.
The Revealer “Seige of Paris Balloon Flights”, Spring 1990, Bill Murphy