Engel,E. u. K.Schellbach. 21 copper plates on descriptive optics. Halle, Schmidt 1856. fol. with 21 folio-sized copper plates. Dplblgr. title. Central hardcover (rubbed and worn). Cf. Poggendorff II, 783 (on Schellbach). - Without the text volume. - Somewhat spotty, n.d.

Composed of several subsidiaries, the Drouot Group is a major player in the art market. Hôtel Drouot, located in the heart of Paris, has been the world's largest public auction center since 1852. 15 salerooms are available to more than 70 auction houses. The emulation generated by an annual offer of 230,000 artworks from 21 major specialities - from Antiquity to street art - attracts some 3,000 visitors every day. The Group's digital platform, Drouot.com, offers digital sales - Live auctions (live broadcasting and participation in auctions), Online-only auctions (dematerialised auctions) and Buy Now sales (sales of lots at fixed prices). Nearly 2 million items are offered annually by 600 auction houses. Auction news is reported every week in La Gazette Drouot, the leading weekly magazine for the art market and culture published by Auctionspress.