NATURAL PHILOSOPHY. 191 



traced by the light. Among the specimens he sent, there were some 

 copies of light tissues ; of crapes folded double, in which the wave-line 

 of the threads that characterize crapes were reproduced with a charm- 

 ing delicacy. It is evident Mr. Talbot has found a burin which will 

 remain very docile to the indications of light, whenever the latter shall 

 have to mark only the lines of bold demarcations between black and 

 white ; but when it is necessary to reproduce gradations of shades, such 

 as those which essentially constitute the images formed in the dark 

 chamber, it may be feared the value of the reactive's attack shall not 

 correspond to the value of the shade sought to be represented. It is 

 especially in vigor that all these purely chemical actions produce in- 

 sufficient effects. The quantity of metal dissolved is, it may be granted, 

 proportional to the value of the shade sought to be represented ; but 

 beyond a certain limit, the desired effect does not increase ; and if the 

 reactive eats the deeper, it does not increase the artistic effect. This 

 Mr. Talbot feels sensibly ; he has neither overlooked, nor sought to 

 diso-uise this truth. He has even indicated that he is thinking on some 

 way of using an artificial grain, to increase the available extension of 

 the scale of shades. 



The communication of the results of Mr. Talbot to the public has 

 induced the publication of a different process devised by MM. Niepce 

 de St. Victor and Lemaitre. The method they employ is but an ex- 

 tension of that used by the partner of Daguerre, M. Joseph Niepce, 

 when he endeavored to take advantage of Judea bitumen. M. Niepce 

 engraved only on tin ; MM. Niepce (nephew) and Lemaitre operate 

 on steel. After having suitably cleaned, and half-scoured the metal, 

 they spread on its surface with a roller covered with skin, a varnish of 

 Judea bitumen, or asphaltum, dissolved in essence of lavender, which 

 they then dry by a gentle heat and in obscurity. Upon the plate thus 

 prepared, they applied the face-side of positive or negative photo- 

 graphic proof upon albumened glass, or upon waxed paper, and ex- 

 posed them to the light, sufficiently long to produce a counter-proof ; 

 a quarter of an hour in the sun, an hour in diffused light, is enough to 

 terminate the operation. To bring this counter-proof out they next 

 employed a dissolvent, composed of three parts of rectified oil of nap- 

 tha, and one part benzoin, whose action is arrested at the proper 

 point by pouring water upon the plate. Then commences the opera- 

 tion of engraving, properly speaking. A first eating is effected by a 

 mixture composed of one part nitric acid, eight parts distilled water, 

 and two parts alcohol. This first eating is intended to indicate only 

 the engraving, for it could not, even were it prolonged, produce 

 vigorous lines. It is then necessary to dry the plate and deposit on it 

 what engravers call a grain of resin. This is a fine resinous powder, 

 which at first is suspended in the air by agitation and then allowed to 

 fall upon the metal like dust upon an article of furniture. The plate 

 being lightly heated, the resin attaches itself to it, and allows the oper- 

 ator to perform another, a vigorous eating, and be certain they shall 

 obtain the grain necessary to retain the ink and form a fine black. 

 The result of ah 1 these operations is a plate engraved, as it were, in the 



