140 DOVE ON THE ELECTRICITY OF INDUCTION. 



cylinder, which, from what has been stated before, and particu- 

 larly when it has a certain thickness, has a weakening effect, 

 there will be, for wires of a definite thickness, a certain number 

 Avhich is quite inactive. Such an inactive combination of wires 

 of the thickest kind of wire was actually very nearly obtained 

 for a certain battery charge. This number must therefore be 

 exceeded when wires are chosen for testing the increasing action 

 of another substance, and the number must be ascertained by a 

 preliminary experiment. 



2. Steel magnetized by the induced current. 



To avoid anomalies, thick needles were chosen, and the length 

 of the wire remained unchanged ; a constant charge was always 

 communicated to the battery by means of a unit jar. 



53. If the equihbi'ium of the current is destroyed, with com- 

 pensating spirals, by the insertion of a conducting substance 

 into one of the spirals, the polarity of a steel needle magnetized 

 by the current in excess shows, that the current proceeds 

 from the empty spiral when the inserted substance* is a foil of 

 iridium, platinum, gold, silver, or a rod of copper, brass, tin, 

 zinc, lead, or an alloy of 1 copper and 1 bismuth, of 3 copper 

 and 1 bismuth, of 3 copper and 1 antimony, of 1 zinc and 1 

 bismuth, of copper, tin, lead, zinc and antimony, of lead and 

 iron, of brass and iron, of bell-metal ; lastly, strips of copper and 

 antimony melted together crossways, of bell-metal and antimony, 

 of antimony and bismuth. The equilibrium of the current re- 

 mained undisturbed when this rod was composed of antimony 

 or of bismuth, or of an alloy of 1 bismuth and 1 antimony, or of 

 3 bismuth and 1 antimony. On the contrary, the polarity was 

 in the direction of the current proceeding from the filled spiral 

 when it contained an unenclosed bundle of wire, or one enclosed 

 in an entire tube, or a column of steel, iron, or tinned iron discs, 

 a solid cylinder of forged iron, of soft or hard steel, of white 

 or gray pig iron ; and lastly, a rod or tube of nickel. A division 

 of the mass of iron into wii-es increases in an extraordinary man- 

 ner the magnetizing effect ; for bundles of wire opposing cylinders 



* The results which were obiained when that metal, which, in the form of a 

 rod, was non-magnetic, was inserted into the magnetizing spirals in the form of 

 an insulated bundle of wire, will be given afterwards at § 62. 



