Siege of Paris night balloon. 19th-century illustration of a balloon ascent by night during the Siege of Paris in the Franco-Prussian War (July 1870-May 1871). The flights distributed mail (upper left) and carrier pigeons (upper right). Cigarette paper confetti, a paper streamer and a wind vane help assess wind direction. During the siege, 168 people, 3 million letters, 363 pigeons, and 5 dogs, left Paris on 66 balloons. The flights were with coal gas, which didn't require heating. Artwork from 'Aerostation - Aviation' (1911) by French civil engineer Max de Nansouty (1854-1913), part of the 'Les merveilles de la science' series of 1867-1891 by Louis Figuier.