342 SUBMARINE CABLE LAYING AND REPAIRING. 



resistance about 7^ ohms per knot; while the cores have a 

 capacity of 0*3045 microfarad, and 2,000 megohms per knot 

 at 75° F. 



The testing room on the "Alert" is remarkable for the 

 very few instruments used. Instead of a couple of reflecting 

 galvanometers and a mirror, there are only one Morse instru- 

 ment and a simple compass card galvanometer. The latter 

 stands on a small table mounted on gimbals, and is found 

 quite sensitive enough for all the tests required, as every- 

 thing is done by null methods on the bridge. The loop test 

 is frequently in use, so many of the cables being multiple with 

 spare insulated conductors to use as returns from the metallic 

 circuit. In localising faults in single cables, and breaks in 

 multiple and single-core cables, when no insulated return con- 

 ductor is available, it is found that the well-known "polar" 

 tests of Mr. Lumsden (chief electrician to the " Monarch ") are 

 more to be relied upon than any other methods. These tests 

 are fully described in " Kempe's Testing " and " CuUey's 

 Telegraphy." The Mance test is seldom used except as a 

 check, and faults of high resistance are rare except in multiple 

 cables, in which case they are readily localised by the loop. 

 Insulation of cables after repair is proved on the bridge. On 

 the wall is fixed a terminal board with six insulated terminals 

 leading to cable in tank and six to bows, so as to be prepared 

 for multiple cables. Battery commutators are also fixed for 

 changing battery power, the cells used being Leclanche. As 

 far as testing is concerned this completes the entire kit ; while 

 for speaking to shore, the distance being comparatively short, 

 the Morse instrument is all that is required. A smart repair 

 was eflfected on one of the Channel cables by this vessel on 

 November 25, 1891. Leaving Dover Harbour at 4.45 a.m. for 

 South Foreland, she proceeded to the position of break, 12 

 miles out, grappled for the two ends, and had the circuits 

 through at 6.45 p.m., arriving back at Dover at 9.30 p.m. 

 same day. The distance steamed was 32 miles in all, and the 

 time from leaving to her return to harbour 16f hours, and 

 this with four large joints to make. 



While referring above to the cables to Belgium and France 

 kept in repair by this vessel, it may be of interest to note 

 that two very old cables are amongst their number, and 



