196 



THE WORLD'S ADVANCE 



be chafed through in short order. Ac- 

 cordingly, the bottom of the sea is care- 

 fully surveyed beforehand, and the 

 smoothest route selected. 



These soundings not only reveal the 

 contour of the ocean floor, but they also 

 determine the chemical quality and the 

 temperature, both of which have a de- 

 cided influence upon the life and the be- 

 havior of a cable. If the examinations 

 should prove that the ocean floor con- 

 tains chemicals injurious to the protec- 

 tive covering, a wide detour is made. 

 The matter of volcanic heat is -as inter- 

 esting as it is troublesome. Heat lowers 

 the electrical conductivity of a wire as 

 well as the insulative ability of the gutta 

 percha ; moreover, it shortens the life of 

 that insulation to a serious extent. An 

 ingenious sounding machine, invented by 

 Lord Kelvin, is used for making the 

 surveys. 



Landing the Shore Cable 



As I have explained, the laying of a 

 cable between two continents does not 

 consist merely of tying one end to a post 

 on one shore, and paying it out while the 

 vessel steams at top speed to the oppo- 

 site side. The numerous steps of the 

 process are based on long scientific expe- 

 rience, and they are carried out with 

 painstaking attention to the smallest de- 

 tails. 



The shore end of the cable is usually 

 landed by means of rafts and india rubber 

 buoys, which are anchored to the bottom. 

 A trench running from low-water mark 

 to the cabll hut is dug and the cable 

 laid in it and covered. 



When the ship is finally under way, the 

 deck presents a scene of lively interest. 

 The cable is dragged into the water from 

 the storage tanks, like thread from the 

 paunch of a spider. Between the drum 

 and the sheaves at the stern, over which 

 the cable slips into the water, stands the 

 dynamometer. This instrument registers 

 the strain to which the cable is sub- 

 jected; it is, so to speak, the finger on 

 the pulse of the entire enterprise. 



As deeper water is reached the weight 

 of the cable increases, and brakes must 

 be applied to the drum. In 2,900 fa- 

 thoms, with the ship progressing at the 



usual rate of eight knots, more than 

 twenty-five miles of cable are in suspen- 



sion. 



// the Cable Should Break! 



Near the drum from which the black, 

 snake-like reel is uncoiling, the testing 

 room is situated. Here, an expert elec- 

 trician bends over a table littered with 

 gleaming instruments. An electrical con- 

 nection is made between the cable and 

 a delicate receiving instrument the 

 mirror galvanometer. Every fifth min- 

 ute an electrical impulse is sent out from 

 ashore, and the spot of light of the gal- 

 vanometer flutters back and forth. As 

 the cable sinks into the freezing-cold 

 water at the ocean bottom, the insula- 

 tion steadily improves, and the spasms 

 of the point of light weaken until it 

 finally sinks almost to the zero point. A 

 defect in the insulation is indicated by 

 a sudden violence of the light spot, and 

 the repair is quickly made. 



When the first drum is uncoiled tl^e 

 vessel is brought to a stop, and the deli- 

 cate task of splicing the two cable ends 

 is performed. To the observer, an ex- 

 aggerated amount of pains seems to be 

 taken in splicing a deep sea cable, but 

 every precaution is absolutely necessary. 

 Air holes in the insulation,' no matter 

 how tiny, when they are subjected to the 

 enormous pressure of the sea will burst, 

 water will rush in and the cable will 

 be useless. 



When a storm comes, the odds are 

 heavily in favor of losing a cable. To 

 avert such a mishap, buoys are slung in 

 the rigging ready to be lowered and at- 

 tached to the broken line at a moment's 

 notice. In spite of this precaution, the 

 cable may snap, as the ship pitches and 

 rears, and slip overboard. Its recovery 

 then resolves itself into a search of long, 

 anxious days often weeks and occa- 

 sionally months. The ocean bottom must 

 be dragged with grappling hooks a 

 blind, groping, discouraging task. For 

 that reason, very naturally, the shallow- 

 est possible route is selected. 



During the preliminary surveys for 

 one of the trans-Pacific cable routes, a 

 "valley" nearly six miles deep was 

 sounded, off the island of Guam. The 



