26 Electric Light 



of the magnet to the South. The current flows in the ring 

 downward in the side nearest to us. When the ring approaches 

 the centre of the magnet, the current gradually gets weaker, by 

 reason of the fewer number of " lines of force" being embraced 

 within it. The current begins to circulate in the ring in the 

 opposite direction, after the centre of the magnet has been 

 passed. The intensity at which the current flows in the ring is 

 due to two things, namely the speed at which the movement is 

 made along the magnet, and the " strength" of the magnet 

 itself. A similar result occurs if the ring is made to move in 

 the arc of a circle between the poles of a horse-shoe magnet, as 

 shown in Fig. 6. In the next diagram (Fig. 7), the horizontal 

 lines between the poles of a horse-shoe magnet are supposed to 

 represent the " lines of force" ; it will be observed that when 

 the ring is perpendicular to these lines, it encircles the largest 

 number ; but when angled, the number decreases, thus pro- 

 ducing a fall in the potential of the current. 



It is possible to obtain all the effects of a magnet, although 

 no iron or steel may be present. If, for instance, a wire is coiled 

 into a ring or helix, and a current is caused to traverse it, the 

 air space in the centre becomes filled with magnetic lines of 

 force. Some electrical machines are constructed in this manner, 

 so that lightness of the moving parts and ventilation may be 

 obtained, besides avoiding what are termed Foucault or wasteful 

 currents, which sometimes arise if iron is employed without due 

 precaution having been taken in the construction. In the 

 earlier machines, these wasteful currents in the iron itself proved 

 highly objectionable, causing much power to be absorbed use- 

 lessly ; but in good machines of the present day, iron is em- 

 ployed with great advantage, and without any wasteful currents 

 being generated to signify. 



Machines may be divided into two classes — direct current and 

 alternating— and these may be subdivided into magneto and 

 dynamo generators. In direct current machines, the electricity 

 always flows along the conductor in one direction, but with 

 alternating dynamos, the current flows in one direction, and 

 then in the reverse, but the changes in direction amount to an 

 immense number per minute, up to ten or twenty thousand. 



