474 FARM MOTORS 



through a magnetic field a current will be set up. This 

 is the most important part of electricity, for upon it is- 

 based the operation of nearly all forms of commercia* 

 electrical machinery. 



633. Currents induced in a coil by a magnet. A sensi- 

 tive galvanometer is connected in a circuit with a wire 

 (Fig. 355) in such a manner that the galvanometer is not 

 affected by the magnet and yet the wire can come into 

 the magnetic field. If that part of the wire between A 

 and B be very quickly moved down across the field the 

 galvanometer needle will be deflected. When the needle 

 comes to zero and the wire is moved across the field in 

 the opposite direction the needle is again deflected, but 

 the opposite way. If the wire be moved into the mag- 

 netic field and held still the needle will come to zero and 

 remain there until the wire is set in motion. Again, if 

 the wire is moved back and forth across the magnetic 

 field the needle will vibrate back and forth across zero, 

 showing that there is a current but an alternating one. 



When the backward and 

 forward motions of the wire 

 have become fast enough the 

 needle of the galvanometer 

 will practically stand at zero, 

 only giving enough vibration 

 to show that there is an al- 

 ternating current affecting 

 it. By trial the following re- 

 sults will be obtained : 



i. When the magnet is 

 moved and the wire held sta- 

 tionary the same results are 

 noted. 

 FIG 255 2 - When the position of 



