Primary Laws. 85 



illustrated as follows : — In passing a compass along 

 a level bar-magnet we reach a point where the force 

 is equal, and the needle lies east and west instead of 

 north and south. This point, if measured, proves to 

 be the centre of the bar. If the compass be moved 

 either way even in the slightest, the needle also 

 moves. In a magnetic battery, similarly, the force is 

 from the dissolving materials in the battery to the 

 poles or extremity of the wires. This law is a potent 

 one in organic life, as we shall show in vegetal and 

 animal evolution, for all organisms possess a virtual 

 magnetic battery in their vacuole or stomach, in which 

 all their life or energy is generated, and from which 

 it is distributed to the extremities. 



Section 5. Fifth Law : Magnetic Induction : 



Definition : Every magnet both attracts and repels 

 every other magnet, but the greater governs the 

 lesser. 

 By this law the energy of a magnet varies accord- 

 ing to its size and density, the greater magnet revers- 

 ing the polarity of the lesser. 



The facts of magnetic induction are numerous and 

 familiar. For instance, a needle suspended near a 

 magnet is attracted by either pole, and by both head 

 and point indifferently ; but by drawing it over a 

 magnet and producing in it magnetic induction, it 

 becomes a magnet with a definite polarity. From 

 thenceforth it is attracted and repelled only polarly. 

 The scientific explanation of induction is as follows:* 

 * "Magnetism," Prof. Chrystal. Ency. Brit. 



