Daguerreotype Plates. 19 



I have not seen any plates thus prepared, but the few ex- 

 periments which I have made with nitric acid, have given 

 me a burred and imperfect outline ; and I have experienced 

 extreme difficulty of manipulation from the circumstance of 

 the acid never attacking the plate uniformly and simulta- 

 neously. My object, however, in this communication, is not to 

 find fault with a process which I have never perhaps fairly 

 tried or seen tried by experienced hands, and the inventor of 

 which deserves the gratitude of all interested in physical 

 science ; but to make public another, which possesses the ad- 

 vantage of extreme simplicity, which any one, however un- 

 skilled in chemical manipulation, may practise with success, 

 and which produces a perfect etching of the original image; 

 so much so, that a plate thus etched can scarcely be distin- 

 guished from an actual Daguerreotype, preserving all the mi- 

 croscopic delicacy of the finest parts of the impression. 



One sentence will convey the secret of this process ; it is to 

 make the Daguerreotype the anode* of a voltaic combination, 

 in a solution which will not of itself attack either silver or 

 mercury, but of which, when electrolyzed, the anion will at- 

 tack these metals unequally. This idea occurred to me soon 

 after the publication of Daguerre's process ; but, being then 

 in the country, and unable to procure any plates, I allowed 

 the matter to sleep; and other occupations prevented for some 

 time any recurrence to it. Recently having heard much con- 

 versation as to the practicability or impracticability of Da- 

 guerreotype engraving, I became anxious to try a few experi- 

 ments in pursuance of my original notion; and for this pur- 

 pose applied in several quarters for Daguerreotypes ; but, 

 thanks to the exclusiveness of M. Daguerre's patent, I found 

 that to procure a sufiicient number of plates for any reason- 

 able chance of success was quite out of the question. 



On mentioning the subject to Mr. Gassiot, he with his 

 usual energy and liberality, offered to procure me a suffi- 

 ciency of Daguerreotypes ; and it is owing to his zealous and 

 valuable cooperation that I have been able to get such definite 

 results, as appear worth publication. 



Five points naturally present themselves to the considera- 

 tion of the experimenter on this subject : first, the quantity, 

 of the voltaic current ; secondly, its intensity ; thirdly, the di- 

 stance between the anode and cathode ; fourthly, the time 



• Strictly speaking this is a misapplication of Faraday's term : he applied 

 it to the surface of the electrolyte ; as, however, all continental and man}-. 

 English writers (among whom 1 may name Whewell) have applied it to the 

 positive electrode, and as an expression is most needed for that, I have not 

 hesitated so to apply it. 



C2 



