APPARATUS FOR THE ELECTRIC LIGHT. 151 



head of soft iron, and at a suitable distance a head ot in- 

 sulating substance. The external extremities of the cores 

 were covered with insulated copper wire, and were connected 

 together, as well as to the principal wire (or to the generator), 

 in such a manner as to produce two opposite magnetic poles. 

 Between the soft iron heads and the coils spirals of finer 

 wire were wound, the fineness depending on the tension re- 

 quired. 



To one of the iron heads an iron arm was jointed capable 

 of turning and being applied to the other head, and thus 

 magnetically connecting the N. and S. poles. In a system 

 thus arranged, if a current is sent through the principal wire, 

 and quickly reversed in the opposite direction, the polarities 

 of the magnetic cores will change, and these changes will 

 produce an induced current of high tension in the smaller 

 coils ; this second current, if it is carried to a lamp by suit- 

 able wires, will maintain the carbon or platinum in a high 

 state of incandescence. Two or four induction coils may be 

 connected together for lights of the highest power. 



