since about Victorian times (roughly 1837 on)+ photographs
The Santos-Dumont airship dipicted (http://2.bp.blogspot.com/_dLSVgS5AxBI/S8ifNyxMnwI/AAAAAAAAqao/kjKUVy5hBfE/s400/Sd_num6_rounding_tower.jpg) is not his No 6, in which he won the prize. Rather, it is of No 5 - a previous similar airship, which he also flew around the Eiffel tower. See http://www.pbs.org/wgbh/nova/space/my-first-balloon-ascent.htmlHats off to the people who got it right. Note the small differences in envelope form and rudder shape!Cheers, Charles
Thank you very much for that.