On mentioning the subject to Mr. Gassiot, he, with his usual energy and liberality, offered to procure me a sufficiency of Daguerreotypes; and it is owing to his zealous and valuable coöperation that I have been able to get such definite results as appear worth publication. Five points naturally present themselves to the consideration of the experimenter on this subject: first, the quantity of the voltaic current; secondly, its intensity; thirdly, the distance between the anode and cathode; fourthly, the time during which the process should be continued; and fifthly, the solution to be employed. 1st. With regard to the first element or quantity, many previous experiments had convinced me that, to give the maximum and most uniform quantitative[B] action of any voltaic combination, the electrodes should be of the same size as the generating plates; in other words, that the sectional area of the electrolyte should be the same throughout the whole voltaic circuit. It seems strange that this point should have been so generally overlooked as it has been; an electrician would never form a battery, one pair of plates of which were smaller than the rest; and yet the electrodes, which offering of themselves a resistance to the current, from the inoxidability of the anode, are, _a fortiori_, a restriction when of small size, have generally been formed indefinitely smaller than the gene, rating plates; I, therefore, without further experiment, applied this principle to the process about to be detailed. [B] I say the quantitative action; for where great intensity is required, as in decomposing alkalies, &c., it may be advisable to narrow the electrodes, so as to present a smaller surface for the reaction of the liberated elements. 2nd. _The intensity of the voltaic current._--Here it appeared to me that, as in the electrotype, where the visible action is at the cathode, a certain degree of intensity throws down metal as a crystal, an increased intensity as a metallic plate, and a further intensity as a pulverulent mass; that degree of intensity which would show on the negative deposit the finest impressions from the cathode, would also produce on the anode the most delicate excavations, and consequently, an intensity which would just fall short of the point of evolving oxygen from the plate to be etched, would be the most likely to succeed; this point was not, however, adopted without careful experiment, the more so, as in one instance Mr. Gassiot succeeded in procuring a very fair etching with a series of ten pairs of the nitric acid battery; however, the results of repeated experiments, in which the intensity has been varied from a series of sixteen pairs to one of the nitric acid battery, were strongly in favor of the above idea, and, consequently, went to prove that one pair gives the most efficient degree of intensity for the purpose required.