Submarine Cables. 155 



some kind of armor. In 1851 another cable 

 was laid between these two points, containing 

 four conductors insulated with gutta-percha, 

 and over all was an armor of iron wire. 

 Twenty-one years later this cable was still 

 working, and for all we know is working now. 

 After this successful demonstration other 

 cables were laid for longer distances. 



These short-line cables served to demon- 

 strate the relative value of different material 

 for insulating purposes under water, and it 

 has been found that gutta-percha possesses 

 qualities superior to almost every other mate- 

 rial as an insulator for submarine cables, al- 

 though there are many better materials for 

 air-line insulation. Gutta-percha when ex- 

 posed to air becomes hardened and will crack, 

 but under water it seems to be practically in- 

 destructible. 



Ocean telegraphy really dates from the lay- 

 ing of the first successful Atlantic cable. 

 There were many problems that had to be 

 solved, which could be done only by the very 

 expensive experiment of laying a cable across 

 the Atlantic Ocean. In the first place a sur- 

 vey had to be made of the bottom of the ocean 

 between the shores of America and Great 

 Britain. The most available route was dis- 

 'd by Lieutenant Maury of the United 

 e Navy, who made a series of deep-sea 

 iings, and di.-roven.-d that, from New- 



