6 THE FLOOR OF THE OCEAN 



This difference explains why there is dry land, why human life 

 is possible. 



Dimensions of the Ocean 



Man has inherited the earth and he has made good progress 

 in picturing his inheritance. The nineteenth century began 

 adequate charting of ocean depths, and here again the initial 

 stimulus was commercial, practical. The dangers of the deep 

 led national governments, particularly the British, to spend 

 millions in sounding the sea with lead and line. Within the 

 last twenty years instruments ensuring greater accuracy and 

 incomparably greater economy in operation have come into 

 use. Now the true shape of the sea bottom is being disclosed at 

 a rate undreamed of as late as the year 1920. 



The improved way of measuring depth is by echo-sounding 

 or sonic sounding. 1 A resonant blow is struck on the hull of a 

 ship at an accurately determined moment of time. The result- 

 ing sound wave speeds to the sea bottom, is there reflected back 

 to the ship. The times of departure and arrival are registered 

 to the hundredth of a second. Knowing the velocity of sound 

 in the water, it is an easy matter to calculate the length of the 

 double journey and ultimately the depth of water. The sonic 

 sounder can be used in a properly equipped steamship, even 

 while plowing its way from port to port. Thus thousands of 

 good readings of depth at as many different points are possible 

 during a single voyage. 



No less essential is the fixing of latitude and longitude for 

 each echo-sounding. In deep water, far from land, the older 

 methods of the navigator — observation of sun or star and dead- 

 reckoning by log or revolutions of propeller — are still neces- 

 sary. In shallower water and to distances up to 200 miles from 

 shore, location of the sounding ship is now being determined 

 by one or more of three methods, bearing the respective names, 



