238 SEC. 7. LIGHT. 



952b. Photolithography. 



The Topographical Department of the Imperial Russian 

 General Staff, St. Petersburg. 



Transfer on stone of a printing picture, well covered with ink, which has 

 been produced on a gelatine ground rendered primarily sensitive by double 

 chromate of potash. 



Reproduction of a Hebrew manuscript of the 10th century, belonging to the 

 Imperial Russian Public Library. 



952c. Helio-Engraving. Sediment of galvanic copper on a 

 photographical gelatine relief. 



The Topographical Department of the Imperial Russian 

 General Staff, St. Petersburg. 



Copies of a heliographical edition of the survey of Bessarabia, on the scales 

 of 1 : 100,000, and 1 : 126,000, and the survey of Finnland, scale, 1 : 42,000; 

 map of Khiva, scale, 1 : 580,000, transferred on stone, and prepared as colour 

 print. 



952d. Examples of Heliographic and other Processes. 



Imperial Establishment for the preparation of official 

 papers, St. Petersburg. 



1 . Portfolio of heliographic copper-plate and mezzo-tint engravings by the 

 process of G. Scamoni (manager of the Heliographic Department of the 

 Establishment), containing : 



27 reproductions of historical portraits ; 



10 reproductions of fine engravings ; 



12 reproductions of etchings ; 



8 reproductions of drawings executed with pen and ink, water-colour, 



and crayon ; 



17 reproductions of pen and ink drawings ; 

 6 reproductions of wood engravings. 



2. Heliographic plate in electrotyped copper. 



3. Heliographic plate in electrotyped iron. 



4. Typographic printing form in electrotyped iron, from type. 



5. Typographic printing form in electrotyped iron, net-work from type. 



6. Typographic printing form in electrotyped iron, net-work from relief. 



7. Typographic printing form in electrotyped iron, guilloched net-work. 



8. Typographic printing form in electrotyped iron, id-annealed. 



9. Glass plate, with the surface irregularly broken up into floral and 

 other forms through a coating of gelatine ( millimeter thick), springing up 

 from it when dried at a temperature of about 70 C., thereby producing a 

 form from which an inimitable printing-plate can be made. 



10. Handbook of heliography, by G. Scamoni. 



b. PHOTOGRAPHIC APPARATUS. 



953. Photographic Lenses for Landscape, Architec- 

 ture, and Copying, showing progressive improvements from the 

 original single meniscus lens : 



(a.) Single meniscus lens, used from 1851 to 1861. 

 (b.) Triplet, consisting of front combination. Double convex 

 crown and plane concave flint ; middle combination. 



