242 EXPERIMENTAL INVESTIGATIONS. 



allowed the matter to sleep ; and other occupations prevented 

 for some time any recurrence to it. Recently having heard 

 much conversation as to the practicability or impracticability 

 of Daguerrotype engraving, I became anxious to try a few 

 experiments in pursuance of my original notion ; and for this 

 purpose applied in several quarters for Daguerreotypes ; but, 

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

 that to procure a sufficient 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 sufficiency 

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

 co-operation 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 

 distance between the anode and cathode ; fourthly, the time 

 during which the process should be continued ; and fifthly, 

 the solution to be employed. 



i. With regard to the first element, or quantity, many 

 previous experiments had convinced me that, to give the 

 maximum and most uniform quantitative* action of any vol- 

 taic 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 inoxida- 

 bility of the anode, are, a fortiori, a restriction when of small 

 size, have generally been formed indefinitely smaller than the 

 generating plates ; I therefore, without further experiment, 

 applied this principle to the process about to be detailed. 



* I say quantitative action ; for, where great intensity is required, as in decom- 

 posing alkalis, &c., it may be advisable to narrow the electrodes, so as to present 

 a smaller surface for the reaction of the liberated elements. 



