1879.] 
The Electric Light for India. 
305 
primary current varies, are equal, and therefore, as they are 
invariably opposite to each other, they neutralise one 
another entirely, which will have the desired effect of a 
quicker regulation of the lamp for any variation of current. 
The iron used in the shunt should have double the weight of 
the iron in the electro-magnet. The sedtion of the wire for 
filling the shunt should be double the sedtion of the wire 
filling the eledtro-magnet. Coil on so many convolutions on 
to the shunt until its resistance becomes equal to the resist- 
ance of the eledtro-magnet. 
For adjusting the quality of the extra currents the fol- 
lowing method should be adopted : — 
Form a Wheatstone bridge two sides of which are formed 
by a mercury rheostat, each side offering about 0*02 S.U. 
resistance. The third side of the bridge is formed by the 
eledtro-magnet of the lamp, the fourth side by the shunt. 
In one diagonal place a dynamo-eledtric machine and about 
one unit resistance, together with a convenient make-and- 
break contadt, best done by a mercury cup. In the other 
diagonal place a Bell telephone of lowest possible resistance. 
One end of this diagonal can be moved along the mercury 
rheostat. Start the dynamo-eledtric machine, listen to the 
telephone, and alter the ratio of the mercury branches of 
the bridge, by shifting along the contadt until the telephone 
is perfedtly silent. Then if, at commencing and stopping 
the current, a strong click is heard, we know it is due to the 
two extra currents not being equal, and as we further know 
that the shunt produces the greatest extra current we make 
this extra current smaller, by shifting along the two poles of 
the shunt an iron wedge, until the telephone is quiet when 
starting and stopping the current. The iron wedge is then 
fixed in its position. This shunt is also to be inside the 
metal cover of the lamp. 
7. The two terminals of the lamp are to be of exadtly the 
same pattern and size as those used in the dynamo-eledtric 
machine. They must not be terminals with hand-screws, 
but strong hexagonal-headed screws with lock-nuts. 
The division of the electric light — i.e., the production by 
the same electro-motor of a number of lights at different points 
of a given space — Mr. Schwendler considers to be imprac- 
ticable from an engineering point of view. Such divisions 
of the electric light can, he argues, only be effected by a 
large sacrifice of total and external light, and moreover this 
loss increases rapidly with the number of lights burned in 
the same circuit. He succeeded in working three Serrin 
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