Joseph-Nicholas Delisle and his nephew by marriage, Philippe Buache, were obsessed by the idea of a vast sea, connected to the Pacific in northwestern North America. Beginning in 1752, Delisle and Buache published a series of maps and memoirs describing this mythical 'Mer de 1'ouest'; some of their maps appeared as late as 1779 in Diderot's Encyclopédie. The 'Mer de l'ouest' had been a strong motive for exploration but as early as the 1740s few others dared place it on a map.

Original map: Carte des nouvelles découvertes au nord de la mer du Sud tant à l’est de la Siberie et du Kamtchatka qu’à l’ouest de la Nouvelle France / dressée sur les mémoires de Mr. Del’Isle ... par Phillippe Buache
Source:  Library and Archives Canada/NMC 21056