392 



THE ELECTRIC TELEGEAPH. 



that, in order to lay a cable successfully the speed of the 

 ship should be precisely that of the outlying cable. Unfor- 

 tunately for the telegraph engineer, this physicist's ideas of 

 the sea bottom do not correspond with the reality ; instead of 

 being level like a street, it is found that as great irregularities 

 occur in the earth under the water as in the earth above it. 

 The sea has its mountains, its valleys, its precipices, as well 

 as the dry land, and over these mountains, and across these 

 valleys, and up and down these precipices, the cable must be 

 laid, and not hung from peak to peak like a tight rope. 

 It must everywhere rest upon the bottom ; if not, it must 

 sooner or later, break by its own weight between the points 

 of suspension, or abrade against the rocks until it is cut 

 through. 



96. The shape of the bottom is ascertained approximately 

 by soundings made with the lead and line. Such soundings 



GREENLAND 



About 670 -niilcs 



Jltml S1U -miles 



LABRADOR 



GREENLAND 



Fig. 179. 



have been made in almost all seas, and diagrams of the 

 bottom, from these data, are constructed before the operation 

 of paying out the cable is commenced. Such, for instance, 

 are the sections (Fig. 179) of the bottom of the sea between 

 Iceland and Greenland and Greenland and Labrador, con- 

 structed from soundings made for the proposed and highly 

 promising North- Atlantic route. The localities where some 



