THE CONQUEST OF NATURE 



In the early days of experiments the loss was so great 

 as to be commercially prohibitive. With the perfected 

 modern dynamo the loss is not greater than fifteen per 

 cent; but even this, it will be noted, makes electricity 

 a relatively expensive power as compared with steam, 

 except, indeed, where some natural power, like the Falls 

 of Niagara, can be utilized to drive the armature. 



A MYSTERIOUS MECHANISM 



The efficiency of the modern dynamo is due largely 

 to the fact that when the poles of the magnet are made 

 to face each other, the lines of magnetic force passing 

 between these poles are concentrated into a narrow 

 compass. With the ordinary bar magnet, as everyone 

 is aware, these lines of force circle out in every direction 

 from the poles in an almost infinite number of loops, all 

 converging at the poles, and becoming relatively sepa- 

 rated at the equator in a manner which may be graph- 

 ically illustrated by the lines of longitude drawn on an 

 ordinary globe. 



It is obvious that with a magnet of such construction 

 only a small proportion of the lines of magnetic force 

 could be utilized in generating electricity. But, as al- 

 ready mentioned, when the magnet is so curved that its 

 poles face each other, the lines of force, instead of widely 

 diverging, pass from pole to pole almost in a direct 

 stream. The strength of this magnetic stream may be 

 increased almost indefinitely by winding the iron core 

 of the magnet with the coil of wire through which the 

 electric current is passed, thus constituting the electro- 



[180] 



