2 optical views, Annam and China, XVIIIth century,... Lot 10

2 optical views, Annam and China, XVIIIth century, framed. "le grand lac de barbarie" (ed. Basset) and "vue de la Cochinchine" (ed. Chéreau), 31 x 48,5 each (marginal tears, small folds, oxidation) The panoramic engravings called "optical views" were widely distributed from the 18th century, around 1740 in Europe, from 3 main production centers, in Paris, London and Amsterdam. They have known a considerable development which was maintained until 1790, then declined strongly from 1820, replaced by other techniques. They can be seen as they are, but are meant to be viewed with a special device called a zograscope. The zograscope allows, with the help of an inclined mirror and a deforming lens, to create a perspective by optical effect, with a predetermined focal length. The views are in fact engraved in such a way that the lines obey a three-dimensional game. It is extremely ingenious.