58 nature's /BMracIce, 



again have the conditions, momentarily, for a 

 current of the opposite polarity, and the needle 

 will swing in the opposite direction because 

 the molecules or atoms have, in their recoil to 

 the natural state, moved in an opposite direc- 

 tion. 



Going back to Fig. 1, let us further study 

 the phenomena under other conditions. In 

 our first circuit (A) there is a battery and a 

 circuit-breaker, which is a common telegraph- 

 key. Now close the key so that a current will 

 be established. (Remember that "current" is 

 only a name for a condition of dynamic 

 charge.) Place a piece of soft iron across the 

 wire at right angles with the direction of the 

 wire, when of course it will be at right angles 

 with the direction of the current, and you will 

 find now that the iron is more or less mag- 

 netic, depending upon the amount of current 

 passing through the wire. If we wind a num- 

 ber of turns of insulated wire through which 

 the current is passing around the iron the 

 magnetism will be increased. In practice 

 there are a certain number of turns and a cer- 

 tain sized wire that will give the best results 

 with a given number of cells of battery (or a 

 given voltage or pressure), operating in a 

 closed circuit of a given resistance. All these 

 questions are worked out mathematically in 

 many standard books on the subject. It is not 

 the intention in these talks to develop the 



