VIMERCATI (Giovanni Battista). Dialogo della descrittione teorica et pratica de gli horologi solari. Ferrara: Valente Panizza, 1565. - In-4, 212 x 160 : (4 ff.), 163 pp. misquoted 171, 1 plate. Tan paper boards, smooth spine (19th century binding). Rare first edition of a treatise by the Italian mathematician Giovanni Battista Vimercati on the theory and practice of solar clocks. The author first sets out the principles of sundial design, adaptable to any latitude and incorporating a variety of time scales (astronomical, Italian, Bohemian and planetary hours), enriched with zodiac signs. It then presents a practical method for tracing these dials with precision, using an innovative device: two styli projecting shadows onto a sheet of paper, enabling sundials to be reproduced quickly and faithfully. Although Vimercati did not explain the geometric foundations of his tool, it was later taken up by Barbaro, who revealed its link with perspective, and then by Jean-François Niceron, who used it to create anamorphoses. This device illustrates the physical link between light and vision, marking a key step between gnomonics and optics. The edition is illustrated with 31 woodcut diagrams, 30 of which are full-page and one fold-out hors texte. It was printed without the P section, the pagination being changed from 108 to 117. Copy in a later hardback, damaged at the edges and at the spine with tears. Tears not missing from title and plate. Worm gallery in the inner margin of pages 45 to 160, some soiling. Old annotation on the top of the title and in some margins. Provenance: label of the ancient and modern bookshop Ernest Thorin (18..-19..), bookseller of the Collège de France and the École Normale Supérieure.