THE EXPLORATION OF THE SEA 



[part I 



but when the line has to be hauled again its weight, plus that of 

 the sinker, may conceivably be great enough to break the line. 

 A further necessity of the line is that it should not offer much 

 resistance to the water on descending or hauling. Again, the 

 sounding machine must be so constructed as to stop automatically 

 when the bottom is reached, and there must be a means of record- 

 ing the length of line run out — that is the depth of the sea in the 

 place sounded. 



In the Lucas, as in all other modern sounding machines, the 

 line is a pianoforte wire which is usually less than one millimetre 

 in diameter. This is polished so as to offer little resistance to the 



Fig. 1. The smaller Lucas sounding machine. By kind permission of the 

 Telegraph Construction and Maintenance Company. 



water in descending or hauling. The line is wound on a reel 

 from which it runs out over a wheel which has a counter recording 

 the number of revolutions, and therefore the number of fathoms, 

 since the diameter of the wheel is known. This arrangement is 

 shewn in Fig. 1, which represents the smaller Lucas machine. 



