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Transactions of the American Institute, 



possible, to the one it is required to test. These wires must then be 

 connected together in a loop at the nearest available station beyond 

 the fault, without ground connection. The resistance of the faulty 

 wire, when perfect, must be ascertained. This may be taken from 

 previous records, or it may be found by a test taken as follows'. 



33. Connect the apparatus as in the diagram (Fig. 2, also frontis- 

 piece), putting the loop in place of the resistance, to be measured as 

 shown in the diagram ; that is, connect the good wire of the loop to 

 III, and the bad wire to IV, and ascertain the resistance as directed 

 (19-21). 



34. Having ascertained the resistance of the loop, arrange the con- 

 nections, as shown in the following diagram (Fig. 3). 



Fig. 3. 



Kow turn the switch A to the right, and note the deflection ; then 

 turn it to the left, and unplug resistance until the same deflection is 

 obtained ; the resistance unplugged, deducted from the total resistance 

 of the loop, and divided by 2, is the resistance of the bad wire between 

 the apparatus and the fault. 



For example, suppose the resistance of the loop to be 1,000 ohms, 

 and 1,000 ohms have been unplugged to balance the needle ; the fault 

 is 450 ohms from IV. Suppose the loop of 1,000 ohms is fifty miles 

 in length, then by proportion 



1,000 ohms : 50 miles : : 450 ohms : 22.5 miles. 



35. "When there is a fault on a line, and there is but one wire, it 

 may be located by the following method : Ascertain, from former 

 record, the normal resistance of the line ; call this r. 



Also the resistance of the defective line, when grounded at the dis- 

 tant end, as before directed (23) ; call this s. 



Also the resistance when open at the distant end, and call this t ; 

 and call the resistance of the wire between the fault and the testing 

 station %; then 



x =s — -\/ ($* + tr) — (ts -^ rs) 



