236 SEC. 7. LIGHT. 



CLASS THE 4TH. 



24. Keproduction of oil painting Diana's toilet, after Devedeux. (Imi- 



tation of photography with salts of silver.) 



25. from nature A hawk ; still life. (Imitation of photo- 



graphy with salts of silver.) 



26. from nature Sevres vases. (Imitation of photography 



with salts of silver.) 



27. from nature Naumachy in the Park Monceaux. (Imi- 



tation of photography with salts of silver.) 



28. of chalk drawing The borders of the Yeres, after 



Allonge. 



29. ,, from nature The bridge of Solferino, Paris. (Imita- 



tion of photography with salts of silver.) 



30. from nature Sevres vases. ( Imitation of photography 



with salts of silver.) 



31. of a print Musings, after de Moussy. 



32. of terra-cotta The Mountebank's, after Deca. 



943. Photo-lithography Process of Simonan and 

 Toovey. Veuve Simonan and Toovey. 



1. Plan of the town of Liege. 



2, Portrait of Archbishop St. Lambert, after an old engraving. 

 3-7. Topographical plans, photographed by Capt. Hanot. 



8-13. Six drawings of the " Campagnie des bronzes " at Bruxelles. 



14-15. Two reproductions from a line drawing by Licot de Nivelles. 



16-19. Four archaeological drawings. 



20. Frontispiece of an ancient MS. 



This is a photo-lithographic process, and depends on the fact that if gum 

 be mixed with potassium dichromate, and when dry be exposed to the action 

 of light, it becomes insoluble. A paper is coated with gum and potassium 

 dichromate, and exposed under the negative of a line subject, or under an 

 etching on glass, having a non-actinic ground. When light has sufficiently 

 acted, the paper which has a faint impression of the lines is placed under a 

 pile of damped paper on the surface of a polished lithographic stone, and sub- 

 mitted to pressure for about an hour. The paper is then removed from the 

 surface of the stone, the insoluble part forming the lines coming away with 

 it. The lines of the engraving are thus left ungummed on the stone. A little 

 olive oil is brushed over the surface, when the gum on the stone has been 

 allowed to dry in a dark room. The surface is next washed, which dis- 

 solves away the gum, leaving the lines of the picture only. The stone 

 is then rolled up with a lithographic roller, and is ready for giving impres- 

 sions. 



944. Specimens of Paul Pretsch's Photo-typography. 



Warren De La Rue, F.R.S. 



945. Electro-chemical Process for reproducing lithogra- 

 phic impressions on copper. M. Erhard. 



A proof freshly pulled from an autograph, lithograph, auto-lithograph, or 

 a copper-plate which is intended to be reproduced, is, by this process, trans- 

 ferred to a copper- plate, and furnishes in a few minutes an intaglio copy of 

 the plate, as clean and good as the original, Avhich is in no wise injured by 

 the operation. 



By means of this process : firstly, it is unnecessary to preserve the cum- 

 brous and fragile lithographic stones ; secondly, a plate in use may be repro- 



