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that by these means a more powerful currentis produced. 
This was discovered by Faraday, and he also discovered that the 
induced current of Electricity is increased or decreased according 
to the number of lines of force that were cut. In this diagram the 
parallel lines represent lines of force. A coil of wite is made to 
move through the magnetic field without cutting any lines of force ; 
no current whatever is generated in the wire. Neither will there 
be any if the coil be so moved in the field as to cut the same num- 
ber of lines of force. But if it be so moved ‘as to alter the number 
of these lines which it cuts as in these two diagrams, a current of 
Electricity will be started, and the greater the difference between 
the number which it cuts, the greater will be the current. This 
principle is of great importance in the construction of the Dynamo. 
In this diagram we have a bobbin of wire moving round in a 
circle from the North pole to the South pole. The dotted lines 
represent lines of force. It is very evident that all the time the 
coil is moving round ina circle, it isnot at any two moments 
cutting the same number of lines of force; consequently all the 
time it is moving, a succession of momentary currents rapidly 
follow each other round the wire, and can be collected. 
fe these preliminary remarks we now come to the Dynamo 
itself. 
These upright blocks of iron, carefully joined at the top, and 
thickly covered with wire are called the Field Magnets, one being 
south the other north. They are also shewn plainly in these 
diagrams. When the Dynamo was in its infancy, the fields were 
made of permanent steel magnets. It has been found however, 
that if temporary soft iron magnets be used instead, the efficiency 
of the machine is greatly increased, chiefly from the fact than an 
electro-magnet can be made’ much more powerful than a per- 
manent one of the same size. The ends of the wires which are 
wound round the fields are not always connected up in the same 
manner. In what is known as the series-wound Dynamo, the wire 
is first connected with one of the brushes, wound round the fields, and 
connected with one of the binding screws; the other binding screw 
is connected with the other brush. From these binding screws the 
Electricity is led through wires to wherever it is required. This 
kind of winding is the best adapted for lighting lamps arranged in 
parallel arc where the resistance is not very great. 
In the shunt-wound as shewn in the diagram, the wire is first 
' connected with one brush, wound round the fields, and then instead 
of being taken’ to the binding screw, connected to the other brush. 
The Electricity is obtained in the main circuit by connecting each 
of the brushes with one of the binding screws. This kind is best 
adapted for lamps arranged in series, where there is a much 
