Frédéric CAILLIAUD (1787-1869), explorer and naturalist; he made several successful expeditions in the upper Nile valley, as far as Abu-Simbel and the ruins of Meroe, becoming the first European to penetrate this region. On his return to France, he turned his attention to natural history, particularly molluscs. Autograph letter signed to Treuttel & Wurtz bookshops. 1 p. ¼ in-4. 8 July 1826. Address on the back with postmarks. On the sale of his work Voyage à Méroé, au Fleuve Blanc au-delà de Fazoql, dans le midi du royaume de Sennâr, à Syouah, et dans cinq autres oasis, fait dans les années 1819, 1820, 1821 et 1822, in 4 volumes of text and 2 of atlas (1826-1827). "I have received your letter of 6 current in which you observe that the discount on the separate text of the work should be the same as that on the plates; I cannot agree to this condition, as I have to realise that the text being detached from the atlas will certainly be detrimental to the sale of these plates; but in order to meet at least part of your request, I will give you the 13th copy, and we are, of course, paying 15 per cent, and the payments will be made closer together than usual. If, under these conditions, you can take on the sale of this work, and you would like me to send you 50 copies so that you have some on hand, please let me know [...]".