No. Vin.] APPENDIX. 183 



origin in the discovery of the constant battery by Professor Daniell, for in 

 that instrament the copper is continually reduced upon the negative plate. 

 In his first experiment, this distinguished author observed, on removing a 

 piece of the reduced copper from a platina electrode, that scratches on the 

 latter were copied with accuracy on the copper. In this experiment we 

 have the electrotype ; but the author, in the first paper detailing his expe- 

 riments, had devoted aU his attention and centred all his energies to the 

 construction of the battery itself, and this valuable fact atti-acted but 

 little of his notice. 



"It was but a short time after the discovery of this battery that 

 Mr. De la Rue experimented on its properties. In a paper printed in the 

 'Philosophical Magazine' for 1836, after describing a peculiar form of 

 battery which he adopts, the following remarkable passage is found : — 

 ' The copper-plate is also covered with a coating of metallic copper, which 

 is continually being deposited ; and so perfect is the sheet of copper thus 

 formed, that, being stripped off, it has the counterfeit of every scratch of 

 the plate on which it is deposited ! ' This paper seems to have attracted 

 very little attention; and, what seems still more singular, the author, 

 although well qualified, from his scientific attainments, to have applied 

 these facts, never thought of any pi-actical benefit to which this experi- 

 ment might lead. 



" In this state the subject remained tUl October 1838, when Professor 

 Jacobi first announced that he could employ the reduction of copper, by 

 galvanic agency, for the purposes of the arts. His process was called 

 galvano-plastic. Immediately upon his discovery being announced in this 

 countiy, in 1839, Mr. Spencer stated that he had executed some medals in 

 copper, to which the public afterwards gave the name of electrotypes or 

 voltatypes, or, what is better, electro-medaUions." The exact value of 

 these primary discoveries " is simply the idea of the application of these 

 facts; but that idea has been everything for Electro-Metallurgy. The 

 only apparatus which Mr. Spencer employed was, in fact, a simple 

 Daniell's battery. He employed various metals for the reception of the 

 precipitated metal, which, however, was nothing new ; but he does not 

 seem to have succeeded with any non-conducting substances. He executed 

 medals, and perhaps duplicate copper-plates ; but he does not give any 

 details as to the different methods for the reduction of the copper in 

 different states, neither did he succeed with the reduction of any other 

 metal. However, to Mr. Spencer the British public are principally in- 

 debted for the idea of the electrotype ; and perhaps the idea, as far as 

 relates to its application in Great Britain, originated entirely with him- 

 seK. I may further notice, in order to confirm what I have already stated, 

 that the galvano-plastics of Jacobi, and the electrotype of Spencer, are not 

 inventions the result of inductive reasoning and laborious research, like 

 Professor Wheatstone's electro-telegraph, or certain elaborate machines, 

 but merely an application of a fact formerly known to DanieU, recorded 

 particularly by De la Rne, and observed by hundreds of others ; that both 

 Spencer and Jacobi could work only in copper, and in no other metal; 

 whilst, had they prosecuted their subject as a science, they woidd have 

 seen that the same laws regulate the reduction of all the metals. 



" Electro-Metallurgy, as first made known to the world by Jacobi and 

 Spencer, was the simplest of all inventions — the application of a fact 



