CHAPTER YI. 
POSITION OP FAULTS, 
Derangements — Faults—The Mirror Galvanometer — Resistance Boxes — 
Methods of finding the position of Faults. 
The derangements of the apparatus that occur in tele¬ 
graphic offices are easily and certainly detected by experienced 
employes. Their intimate knowledge of the connections, paths 
of the currents, etc., soon teaches them the seat and cause of 
the derangement. The receiving and transmitting apparatus 
are moreover also always accompanied by a magnetic needle or 
galvanometer for indicating the passage of the currents, and 
this at once shows whether the fault is in the office or in the 
line. When this magnetic needle is not deflected while the 
currents should be passing in into the line, the defect is in the 
galvanometer itself, in the battery, or in the wires within the 
office. It rarely happens that the apparatus in a well-kept 
office gets out of order. 
The adjustment of the complicated apparatus is usually 
made by the superintendent of the line, and the subordinate 
official seldom assumes the responsibility of a possible stoppage 
of communication. 
Whenever the communications are interrupted outside, the 
cause is a fault in the line. These faults are due to (1) bad 
insulation; (2) to excessive resistance caused by a bad joint, 
or a solution of continuity in the conductor; or (3) finally to 
two wires coming into contact and thus confusing the several 
signals. 
Bad insulation in overhead lines is generally caused by 
broken or soiled insulators, or by the wire touching a tree or 
other object, by which a ground connection is made. When 
bad insulators are used, the defect may extend over a con¬ 
siderable length of the line, whilst contacts of the wire can 
scarcely occur except at a few detached points. In each case 
