60 GENERAL PROPERTIES OF LIVING TISSUES 



On the Construction of the Inductorium. Ex- 

 amine the construction of the inductorium. The 

 primary coil consists of a few turns of thick wire. 

 More turns would increase resistance and self- 

 induction, the counter induction set up in each 

 turn of the primary wire by the passage of the 

 primary current through neighboring turns, 

 without increasing the induction effect in the 

 secondary coil. 



*The iron core adds to the number of lines of 

 magnetic induction which pass through the coils. 

 It has been already shown (page 58) that the 

 lines of magnetic induction produced by the pas- 

 sage of an electric current through a wire are 

 closed circles. If the centre of the coil were 

 filled with air, most of these circles would remain 

 closed about their own wire, for air is not readily 

 permeable to magnetism. But when the iron core 

 is placed within the coil the greater part of the 

 magnetic induction follows the iron (because it 

 is more permeable) from end to end of the core, 

 returning outside through the air. Thus the 

 number of effective lines is increased. A bundle 

 of iron wires is used instead of a solid core, be- 

 cause no induced current is then possible through 

 the mass of the iron, as would be the case in a 

 solid core. Such a current would slow the speed 

 of magnetization and demagnetization. 



