THE LOCALISATION OF BREAKS AND FAULTW. 



475 



difference in the two throws to minimiae any error in reading 

 a few divisiona out. The approximate values of x and the 

 fault will in all probability be kaown from shore tests taken 

 before ship cuts in, but in any case the first rough test will 

 show if R is too large or too little for getting convenient 

 throws. The throws taken at the terminals of the resistance 

 R are compared with the throw given by a standard cell on the 

 same condenser, and the value of P and jj in volts are then 

 found by direct proportion. The E.M.F. of the standard cells 

 used must be corrected for temperature, but no correction is 

 required for any difference in the E.M.F. of the standard cells 

 used on the ship and on shore, provided readings at both ends 

 are converted to volts. In the ordinary course the shore 



Cable 



H'I'l' 



Slides 



Fid. 201. — Measiiremcut of Potentials at Shore Station by Slides iu 

 Clark's Test. 



informs the ship of the added resistance in ohms and the two 

 potentials in volts, and the ship works out the distance of the 

 fault from the shore by the formula given above. 

 For example, shore's figures are 



E = 350 ohms. 

 P-:17-4 volts. 



Then distanca of fault is 



a;—BA~-^=350 X ,— — ~ =^ 500 units from shore. 

 P-p 17-4— 12-5 



And the resistance of the fault is 



5-5 



350 X — 



= 391 units. 



17-4-125 



This method has been applied with uniform success on high 

 resistance variable faults of 5,000 to 30,000 ohm3, the localiaa- 



