246 EXPERIMENTAL INVESTIGATIONS. 



of these exquisite images is destroyed. If, on the other hand, 

 the process be only continued long enough to leave an exact 

 etching of the original design, which can be done to the mi- 

 nutest perfection, the very cleaning of the plate by the printer 

 destroys its beauty ; and, the molecules of the printing-ink 

 being larger than the depth of the etchings, an imperfect im- 

 pression is produced. For this reason it appeared to me that 

 at present the most important part of this process is the 

 means it offers of multiplying indefinitely Daguerreotypes 

 by means of the electrotype. An ordinary Daguerreotype, 

 it is known, will, when electrotyped, leave a faint impression ; 

 but in so doing it is entirely destroyed, and this impression 

 cannot be perpetuated ; but one thus etched at the voltaic 

 anode will admit of any number of copies being taken from 

 it. To give an idea of the perfect accuracy of these, I may 

 mention, that in one I have taken, on which is a signboard 

 measuring on the electrotype plate 0*1 by 0*06 of an inch, 

 five lines of inscription can, with the microscope, be distinctly 

 read. The great advantages of the voltaic over the chemical 

 process of etching appear to me to be the following : 



1. By the former, an indefinite variety of menstrua may 

 be used ; thus, solutions of acids, alkalies, salts, more espe- 

 cially the haloid class, sulphurets, cyanurets, in fact any ele- 

 ment which may be evolved by electrolysis, may be made to 

 act upon the plate. 



2. The action is generalised, and local voltaic currents are 

 avoided. 



3. The time of operation can be accurately determined, 

 and any required depth of etching produced. 



4. The process can be stopped at any period, and again 

 renewed if desirable. 



The time I have given is calculated for experiments made 

 with one pair of the nitric acid battery ; it is, however, by no 

 means necessary that this be employed, as probably any other 

 form of voltaic combination would be efficient. It seems 

 more advisable to employ a diaphragm battery, or one which 

 produces a constant current, as otherwise the time cannot be 

 accurately determined. It is very necessary that the silver 

 of plates subjected to this process be homogeneous. Striae, 

 imperceptible in the original Daguerreotype, are instantly 



