The practical working of the gelatine emulsion process (1880)
Abney, William de Wiveleslie, Sir, 1843-1920, author · London : Piper and Carter · leaf 38
28 GELATINO-BROMO-IODIDE EMULSION. thick plate glass about three feet long by one foot broad, and quarter-inch thick. This we level by means of three mahogany wedges and an ordinary spirit level. To level the shelf, we place two wedges opposite one another. … Fig. 7. The level is placed first across the plate, and the two wedges are altered till the bubble of the level D is cen¬ tral ; the level is then turned lengthways along the plate, and the bubble caused to occupy its proper position by shifting C, not touching A or B. This should cause the plate,…
Photography
Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.
