L'Aérophile Roman numbering
They may have been used for style or convienience but are not historically correct – or so it very well seems. In My Airships
(pub. 1904) Santos writes all project numbers Arabically. I've looked carefully elsewhere and at this time I can find only three other contemporary sources that use a Roman numeral. An article in Harper's Weekly
written by W. L. McAlpin who uses "Santos Dumont VI," the NY Herald refering to photos of №6 as "Santos-Dumont V," and Will's Cigarette Card # 45, printed somewhat later obviously, titled "Santos Dumont's Monoplane, No. XIX." Everyone else uses an Arabic numbering system, almost always preceded with a №, or the common European n°
Physically lettered projects were:
№ 9 "Baladeuse"
№ 14 (on both the original and enlarged envelope)
№ 14 bis
№ 16 (LTA/HTA airship)
№ 18 (wingless hydroplane)
№ 19 "Demoiselle"
A lot of mistaken identity surrounded S-D airships 5, 6, 7 and 8; even still to this day apparently. Santos-Dumont would have known of this at the time. As for an example, he would have seen postcards sold in Paris identified incorrectly - 5 mistaken for 6, 6 being labeled 7 and so forth. So I wonder if he didn't start lettering his airships to help avoid this confusion?
That aside, attached is a scan of an unusual postcard – postally used April 1904 – that makes no sense to me. Is this an Easter card? Hopefully someone can come up with an explanation.