Applied Science 799 



The Generator 



Briefly, a generator consists of a coil or coils of wire, wound 

 on a soft iron core to form a drum-like armature (as it is called) ; 

 while the permanent magnet becomes an electro-magnet, or a 

 number of electro-magnets, capable of creating very powerful 

 magnetic fields. The armature is mounted on a shaft or spindle 

 and revolved at high speed between the magnet poles ; or it may be 

 stationary, the magnets revolving round it. It should be noted 

 that the armature coils do not represent our original wire ring 

 completely, as they form only part of the circuit, the main part 

 of which would consist of stationary wires leading the current 

 wherever it is needed. If the armature itself revolves, it must be 

 put in communication with the stationary part of the circuit by 

 means of brushes flat pieces of metal or blocks of carbon which 

 press upon smooth rings connected with the armature coils and 

 revolving with them. 



Such a machine may be compared to a cylinder having its 

 ends connected with the ends of a pipe. Just as a pump piston, 

 moving to and fro in a cylinder, forces water to and fro through 

 the pipe, so the generator drives electrical energy backwards and 

 forwards through the conducting circuit, the reversals of direction 

 occurring many times a second. 



We may say here that for some purposes alternating current 

 is not convenient. The term dynamo is commonly reserved for a 

 class of generator which is so designed that it pumps current con- 

 tinuously in the same direction through the circuit. The current 

 is then said to be "continuous," or "direct." In dynamos the 

 armature is invariably the revolving part. The brushes which 

 connect it with the circuit do not in this case press on separate 

 rings, but on a single cylindrical drum, revolving with the arma- 

 ture and divided lengthwise into a number of insulated segments, 

 each connected with some of the armature coils. The brushes 

 make contact with it at points half a circle apart, so that if there 

 be, say, twelve segments, they will be in contact with Nos. 1 and 



