Mi*. Faraday on certain Magneto- electric Phenomena. 349 



forming a chain by which the galvanic current, including the 

 multipliers attached to each end of the chain, has to run 

 through a length of wire of nearly 9000 feet. The wire is mostly 

 copper, of the thickness known in trade as number 3, and of 

 which a length of one metre weighs 8 grammes. The wire 

 of the multiplier in the magnetical observatory is of plated 

 copper number 14, of which one gramme gives 2'6 metres. 

 This arrangement is likely to produce the most interesting re- 

 sults. It is wonderful how a single pair of plates placed at 

 the other extremity immediately impart to the magnetic rod 

 a motion equal to considerably more than a thousand divisions 

 of the scale. But what is still more remarkable is, that a pair 

 of plates, of perhaps no more than one inch in diameter, 

 will produce, with the application of mere spring or distilled 

 water, an effect not much less than that produced by a very 

 large pair of plates with the application of a strong acid. 

 This circumstance, however, is after all not surprising, as it 

 only tends to confirm the beautiful theory first established by 

 Ohm. On the other hand, by adding to the number of the 

 pairs of plates the effect increases, and almost in exact pro- 

 portion to it. The facility and certainty by which, through 

 the means of the commutator, the current and the movement 

 of the needle dependent on it are commanded, suggested 

 the idea of trying telegraphic experiments with the apparatus, 

 which have perfectly succeeded with whole words, and even 

 short phrases. Nor is there a doubt that by this means tele- 

 graphic communications might be formed between towns many 

 miles apart ; but this is, of course, not the place where we 

 could enter on a further development of this subject. 



XL VI I. On the Magneto- electric Spark and Shock, and on 

 a peculiar Condition of Electric and Magneto-electric In- 

 duction. By Michael Faraday, Esq., D.C.L., F.R.S., §c. 



To Richard Phillips, Esq., F.R.S., fyc. 

 My dear Sir, 

 TF you think well of the following facts and reasoning, you 

 A will, perhaps, favour them with a place in the Philosophical 

 Magazine. 



When I first obtained the magneto- electric spark*, it was 

 by the use of a secondary magnet, rendered for the time active 

 by a principal one ; and this has always, as far as I am aware, 

 been the general arrangement. My principal was an electro- 

 magnet; Nobili's w T as, I believe, an ordinary magnet; others 



* Philosophical Transactions, 1832, p. 132. [See also Phil. Mag. and 

 Annals, N.S. vol. xi. p. 401, &c— Edit.] 



