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XXXVIII. On Electro-dynamic Induction in Liquids, 

 Bij Professor Faraday, F.R.S. ^-c* 



To Prof. Aug. de la Rive, For. Mem. R.S. &;c. 



Royal Institution, 

 My dear Friend, March 7, 1854. 



YOUR question, " whether I have ever succeeded hi produ- 

 cing induction currents in othei* liquids than mercury or 

 melted metals, as, for instance, in acid or saline solutions V has 

 led me to make a few experiments on the subject ; for though I 

 believed in the possibility of such currents, I had never obtained 

 affirmative I'esults : I have now procured them, and send you a 

 description of the method pursued. A powerful electro-magnet 

 of the horse-shoe form was associated with a Grove's battery of 

 twenty pairs of plates. The poles of the magnet were upwards, 

 their flat end faces being in the same horizontal plane ; they are 

 3*5 inches square and above 6 inches apart. A cylindrical bar 

 of soft iron, 8 inches long and 1'7 in diameter, was employed 

 as a keeper or submagnet : the cylindrical form was adopted, 

 first, because it best allowed of the formation of a fluid helix 

 around it ; and next, because when placed on the poles of the 

 magnet, and the battery connexions made and broken, the mag- 

 net and also the keeper rises and falls through much larger 

 variations of power, and far more rapidly than when a square or 

 flat-faced keeper is employed ; for the latter, if massive, has, as 

 you know, the power of sustaining the magnetic conditions of 

 the magnet in a very great degree when the battery connexion 

 is broken. A fluid helix was formed round this keeper, having 

 12 convolutions and a total length of 7 feet ; the fluid was only 

 0*25 of an inch in diameter, the object being to obtain a certain 

 amount of intensity in the current by making the inductive 

 excitement extend to all parts of that great length, rather than 

 to produce a quantity current l)y largeness of diameter, i. e. by 

 a shorter mass of fluid. This helix was easily constructed by 

 the use of 8"5 feet of vulcanized caoutchouc tube, having an 

 internal diameter of 0*25, and an external diameter of 0-5 of an 

 inch : such a tube is sufficiently strong not to collapse when 

 placed round the iron cylinder. The twelve convolutions occu- 

 pied the interval of inches, and two lengths of 9 inches each 

 constituted the ends. This helix was easily and perfectly filled 

 by holding it with its axes perpendicular, dipping the lower end 

 into the fluid to be used, and withdrawing the air at the upper ; 

 then two long, clean, copper wires, 0-25 of an inch in diameter, 

 were introduced at the ends, and being thrust forward until they 

 reached the helix, were made secure by ligaments, and thus 



* From the Bibliotheque Universelle de Geneve. 

 Phil. Mag. S. 4. Vol. 7. No. 45. April 1854. T 



