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angled lever, to the short horizontal limb of which is fixed 
an armature placed over the poles of the electro-magnet. 
When the movable and fixed carbon holders are brought 
into juxtaposition, and the carbons inserted in them, the 
upper parts of the two carbons are always in contact when 
no current is transmitted through them, as shown by the 
dotted lines in the engraving. 
The contact between the carbons is maintained by means 
of an antagonistic spring inserted in a recess in one of the 
poles of the electro-magnet, and reacting on the under side 
of the armature. One extremity of the coil of the electro- 
magnet is in metallic connection with the base of the carbon 
holder, while the other extremity of the coil is in connec- 
tion with the terminal screw at the base of the instrument, 
