MAN'S CO-LABORER: THE DYNAMO 



magnet which has replaced the old permanent magnet 

 in all modern commercial dynamos. 



An electromagnet may be sufficiently powerful to lift 

 tons of iron. The force it exerts, therefore, is very 

 tangible in its results. Yet it seems mysterious, because 

 so many substances are unaffected by it. You may 

 place your head, for example, between the poles of the 

 most powerful magnet without experiencing any sen- 

 sation or being in any obvious way affected. You may 

 wave your hand across the lines of force as freely as you 

 may wave it anywhere else in space. Apparently 

 nothing is there. But were you to attempt to pass a 

 dumb-bell or a bar of iron across the same space, the 

 unseen magnetic force would wrench it from your grasp 

 with a power so irresistible as to be awe-inspiring. 



Similarly, the armature, when its coils of wire are ad- 

 justed between the poles of the magnet, is held in a vise- 

 like grip by the invisible but potent lines of magnetic 

 force which tend to make it revolve. It requires a 

 tremendous expenditure of energy supplied by the 

 steam-engine or by water power to enable the coiled 

 wires of the generating armature to stem the current of 

 magnetic force, which is virtually what is done when the 

 armature revolves in such a way as to produce electrical 

 energy. Part of the mechanical energy thus expended is 

 transformed into heat and dissipated into space; but 

 the main portion is carried off, as we have seen, through 

 the coiled wires of the armature in the form of what we 

 term the current of electricity, to be re-transformed in 

 due course into the mechanical energy that moves the 

 car. 



[181] 



