166 PHYSICS. 
the alternate attraction and repulsion of bar electro-magnets. The machine 
consists of a wooden frame; the posts, b, b, b, b, carry two rings, cc and hh, 
to whose inner circumference twelve electro-magnets, d, d, d, are fastened 
at equal distances apart. T'welve other electro-magnets, g, g, g, are 
attached to the wheel of the axle,e. All the electro-magnets have projecting 
pieces of iron at their extremities, so that the inner moving system passes 
very close to the outer fixed one. An arrangement, 1, is fastened to the 
axle above the electro-magnets ; it is shown from above in fig. 38. This 
commutator is intended to reverse the direction of the current traversing the 
wires of the electro-magnets twelve times in each revolution; by this means 
the polarity of the electro-magnets is reversed the same number of times. 
The current from the battery enters the machine through one of the. 
conducting wires, s, into the turns of the first fixed electro-magnet, and 
these being connected with each other, the current passes through all the 
coils. From the last bar, a communication at & leads into an arrangement 
shown in fig. 37, which carries the current through the commutator to 
the movable bars. After these coils have been traversed, the fluid passes 
through the second wire of the same arrangement, ¢ ( fig. 37), and through 
the second conducting wire, s, back again to the battery. 
On the introduction of the electric current all the bars become magnetic, 
the fixed system attracting the movable until the two are opposite to each 
other. At this moment the poles of the movable magnets are reversed, and 
the previous attraction becomes a repulsion. The momentum of the 
rotating mass has carried it, however, a little beyond the point where the 
two systems are diametrically opposite; this repulsion then acts to impel 
the movable system in the same direction as before. At the same time the 
magnet thus repelled by one fixed magnet, is attracted by the next fixed one, 
since the windings of the coils are so adjusted as to cause the north and 
south poles of the latter system to alternate at their upper extremities. This 
alternate attraction and repulsion existing between each fixed and movable 
magnet, soon imparts to the axle a rapid and uniform rotation. This 
is communicated to the horizontal axle, p, by means of the bevelled wheels, 
n, m, unless these should be thrown out of gear by the lever arrangement at 
o. The anterior extremity of the horizontal axle carries a pulley, p, with 
rope and hook, q, for raising weights. At the lower end of the vertical axle 
there is a horizontal wheel, rr, with an endless rope passing round it, by 
which means a rotary motion may be communicated to any object, a turning 
lathe for instance. Indeed, the machine was actually used for this purpose 
by its inventor. 
The commutator (pl. 22, fig. 38) consists of a plate of wood with metal 
strips let into its surface. These strips are all connected internally in sucha 
manner that all those lying in the same circle are in metallic communication 
with each other. -Of the four metal rings, the first and second, and the 
third and fourth, are likewise in metallic communication. The two 
extremities of the wire of the movable magnet pass each to one of these 
two combinations. 
The arrangement (fig. 37) is set into the wooden frame (fig. 36) at k, 
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