THE HISTORY OF SOT^IE DISCOVERIES OF 

 PHOTOGRAPHY." 



By Robert Hunt. 



A. Heliograpiiy — line Process of Monsieur Niepce. 



Monsieur Niepce Avas the first inquirer Avho appears to have pro- 

 duced permanent pictures by the influence of the sun's rays. This 

 process — lieliography- — is in many respects peculiar, which renders it 

 necessary, although his preparation was only acted on l\v an exposure 

 of many hours to full sunshine, to give a particular account of it ; 

 the more so, as some points of considerable interest require further 

 elucidation. 



The sul)stance employed by Monsieur Niepce was asphaltum, or 

 bitumen of Judea. He thus directs its jirepa ration : "I about half 

 fill a wineglass with this pulverized bitumen; I pour upon it, drop 

 by drop, the essential oil of lavender '' until the bitumen is completely 

 saturated. I afterwards add as much more of the essential oil as 

 causes the whole to stand about three lines above the mixture, which 

 is then covered and submitted to a gentle heat until the essential oil is 

 fully impregnated with the coloring matter of the bitumen. If this 

 varnish is not of the recpiired consistency it must be allowed to evap- 

 orate slowly, without heat, in a shallow dish, care being taking to 

 protect it from moisture, by which it is injured, and at last decom- 

 posed. In winter or during rainy weather the precaution is doubly 

 necessary. A tablet of plated silver or Avell cleaned and warm glass 

 IS to be highly polished, on which a thin coating of the varnish is to 

 be applied cold, with a light roll of very soft skin. This will im})art 

 to it a fine vermilion color and coA^er it with a \ery thin and ecjual 

 coating. The plate is then placed upon heated iron, which is wrapped 

 around with several folds of j)aper, from which by tills method all 

 moisture had been previously expelled. When the varnish has ceased 

 to simmer the plate is withdrawn from the heat and left to cool and 



o Revised by T. W. Suiillie, U. S. National .Museum, from Cliaptfrs Il-H' of 

 A Manual of Photography, by Robert Hunt. FouiMli cditidii. Ldudon and 

 Glasgow, 1854. Octavo, pp. 329. 



& The English oil ot' lavender is too expensive for this pui'iiose. .\n article 

 sold as the French oil of lavender, redrawn, is very much cheaper and answers 

 iu every respect as well, if not better. 



287 



