T II E 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE, 



[THIRD SERIES.] 



SEPTEMBER 1839. 



XXIX. On the Method of producing Copies of engraved Cop* 



per-plates by Voltaic Action ,- on the supply of mixed Gases 

 for Driimmond's Light, by Electrolysis ; on the Applicatioji 

 of Electro-magnetism as a motive po-joer in Navigation, and 

 on Electro-magnetic Currents. By Dr. M. H. Jacobi : in 

 a Letter to Mr. Faraday.* 

 TT is sometime since, that during my electro-magnetic la- 

 hours, a fortunate accident conducted me to the discovery 

 that we might by voltaic action make copies in relief of an en- 

 graved copper plate, and that a new inverted copy of those in 

 relief might be obtained by the same process, so that the power 

 was obtained of multiplying the copper copies to any extent. 

 By this voltaic process the most delicate and even microscopic 

 lines are reproduced, and the copies are so identical with the 

 original that the most rigorous examination cannot find the 

 least difference. I send you in the accompanying packet two 

 specimens of such plates, which I hope you will accept with 

 kindness. The one which is in relief is the copy of an ori- 

 ginal engraved with the burin; the second is the copy of that 

 in relief, and consequently identical with the original. The 

 third is the original plate, but covered with reduced copper. 

 I had the intention of making a second copy, but unfortu- 

 nately the plates adhere so strongly at times that it is im- 

 possible to separate them. I cannot tell the cause of this in- 

 timate union which occasionally occurs, but it appears to be 

 the case only when the copper at the surface of which the re- 

 duction is effected is brittle, and consequently is lamellar and 

 porous. I may dispense with describing more at large the ' 

 apparatus that I make use of. It is simply a voltaic pair 

 * Communicated by Dr. Faraday. 



Phil. Mag. S. 3. Vol. 15. No. 95. Sept. 1839. M 



