166 SUBMABINE CABLE LAYING AND EEPAIRING. 



the deadbeatness makes the instrument suitable for fault 

 localisation tests. 



Mr. Herbert Taylor (of Messrs. Clark, Forde and Taylor) 

 has devised the following method by which, without alteration 

 to the usual ship and shore connections during submersion, 

 the fall of potential test can be immediately applied in the 

 event of a fault appearing in the submerged portion. The 

 usual ship and shore connections are on Willoughby Smith's 

 system, the apparatus, so far as affects the present test, being 

 arranged as shown in Fig. 82. The slides are connected as 

 in the bridge test, the current from the testing battery divid- 

 ing between the fixed resistance R and cable on one side 



_ Cable. SHORE. 



V. 



000 



r'W\/\AyvVwv\A7 1 a 



Slides 



M 



High Resistance. 

 (Selenium Bar.) 



h|i|i|i|i|iH- 



Fig. 82. — Willoughby Smith's Test, while laying. 



and the slides on the other. The galvanometer is connected 

 as shown with one contact movable on the slides. The zero 

 end of the slides is connected to the testing battery end, so 

 that when balance is obtained the insulation resistance of 

 the submerged portion is indicated continuously and is equal to 



R [ — '- 1 j ohms, 



where s is the slide reading. The ratio — '- can be found at 



° s 



once by a table of reciprocals — that is, by finding the reciprocal 

 of s and moving the decimal point four places to the right. 



Mr. Taylor adds a standard cell to each end and a megohm 

 to the end on shore, with suitable commutators to plug them 



