Submarine Telegraph Cables during Paying -out, 201 



The observer on shore would very soon observe, by the deflec- 

 tion on his galvanometer becoming gradually but very regu- 

 larly lessened, that the conductor had parted, and the end on the 

 shore side was enclosed in the insulator. If, on the other hand, 

 the deflections suddenly ceased, he would further know that the 

 conductor had parted and was exposed. 



In practice it is found preferable, instead of automatically 

 connecting the condenser with the cable and galvanometer, to 

 use an ordinary charging and discharging key, and to perform 

 this test at intervals of every five minutes. According to Mr. 

 Latimer Clark (Electrical Measurement, &c.) this was carried 

 out on the Atlantic cables in 1866, although it was perfectly 

 unknown to the author at the time this article appeared. 



In the present method it is proposed to obtain " continuity "- 

 indications on the shore, and at the same time to measure the 

 tensions of the end at the shore by means of Sir William Thom- 

 son's quadrant-electrometer. 



Now, since the conductor of a cable may be parted with insu- 

 lation still perfect, the electrometer should be capable of show- 

 ing the fall of tension in 20 or 30 seconds on the highest degree 

 of insulation ; but an electrometer with this degree of sensi- 

 bility could not be used in the ordinary way, when the cable is 

 connected on the ship with 100, or any number of cells usually 

 employed; for the tension of the cable at the shore end would 

 repel the needle in one direction completely beyond the range 

 of being read. 



In order to obviate this, the end of the cable is to be connected 

 to one pair of quadrants, and to the other pair a battery in all 

 respects similar to the testing battery on the ship. If the tension 

 of the ship's battery, as found at the shore end of the cable, be 

 such as to balance the opposing battery on the shore, the electro- 

 meter will maintain its zero position ; and if we could be sure of 

 setting up any ordinary testing battery in two places and at 

 different times alike, we should be able at once to obtain a most 

 accurate comparison of the tensions at the two ends of the cable. 

 The shore-electrometer being used in this way, the slightest 

 flaw which could not be possibly recognized on the ship's galva- 

 nometer would be easily detected, and in deep water a long time 

 before it could possibly reach the bottom. 



In this way, by one single observation, the shore obtains a 

 continuity test, an insulation test, and at the same time, should 

 any thing go wrong, the adjustment required to bring the elec- 

 trometer-needle to its zero position supplies the data for locali- 

 zing any defect which might arise. Should the ship wish to open 

 communication with the shore, the same instrument is at once 

 ready to receive a "call" signal, or a complete but simple message. 



