Pigeongrams

A pigeongram
A pigeongram. Source: Museum of the French Postal Service.

The pigeongram was a small microfilm designed to be transported by carrier pigeon.
It was invented during the time of the Franco-Prussian War of 1870 and the Siege of Paris.
Corps 1

On 7 October 1870, Léon Gambetta, France's Ministry of the Interior, fled besieged Paris by hot-air balloon. The minister escaped to Tours, and then Bordeaux.
On 4 November, the system of transporting dispatches by carrier pigeon was inaugurated. Some 302 pigeons (other sources give a higher number of 409) were loaded into the wicker baskets of hot-air balloons. The majority of these pigeons belonged to Paris citizen who patriotically donated them to the services of the authorities.
Sources: www.philatelistes.net
Corps 2

Pigeongram on collodion (a transparent material made from cellulose nitrate in ether and alcohol). Source: Musée colombophile Crespin (Crespin Pigeon-fancying Museum).

After their arrival in Tours (or Bordeaux), they were fitted with small tubes containing 3-4 cm microfilms on collodion (a transparent material made from cellulose nitrate in ether and alcohol). The pigeons were then released as near to Paris as they could get, the idea being they would hopefully reach their original points of departure in Paris. Yet only 50 pigeons or so managed to find their way home. For the pigeons that made it back, the microfilms they delivered were placed between sheets of glass and projected onto a large screen using a magic lantern. The texts were then carefully transcribed then distributed to the intended recipients.

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