I haven't yet been able to get my hands on the 1844 article by Jules Dupuit in "Annales des Ponts et Chauss?es, 6e cahier 1844". But I did find his 1849 follow-up article, repeating, discussing, and expanding his original ideas: "De l'influence des peages sur l'utilite des voies de communication", in: "Annales des Ponts et Chauss?es, nos. de mars et avril 1849". It is on pp.308-390 in the 1877 collection - by the Library of the French Department of Finance - of articles on the political economy of transport and communications, entitled "Des voies de communication en France; recueil de brochures". You can download it - for free: a considerable utility at zero exchange value! - at "gallica.bnf.fr", signature: BNF N0035549_PDF_1_448.pdf . For your convenience, I have also extracted the 1849 article, cropped the pages, and put it on top of the download section in my website at www.condorcet.nl. With kind regards, Marcel Claessen