HOW THE SEA IS SOUNDED. 339 



the water to pass freely through the cylinder so that it expe- 

 riences a minimum of resistance. On striking the bottom, the 

 slackening of the sounding line, which is secured to the ring 

 shown at the upper end in the accompanying illustration, causes 

 the trigger to spring back and release the sling that supports the 

 detachable weight. As the lower end of the sounding cylinder 

 sinks into the bottom a specimen of the soil forces itself through 

 the lower valve and lodges in the interior of the cylinder. When 

 the cylinder is hauled up the valves at the top and bottom are 

 closed by their own weight and the pressure of the water, and 

 the specimen is sealed until its arrival at the surface, when it is 

 removed for examination by unscrewing the upper and lower 

 halves of the cylinder. 



In 1872 Sir William Thomson (Lord Kelvin) succeeded in 

 adapting piano-forte wire to successful use as a sounding line in 

 his navigational sounding machine, and a few years afterward 

 Commander Sigsbee, besides contributing by his inventive genius 

 most of the smaller instruments and implements used in modern 

 deep-sea research, achieved the crowning triumph of the art in 

 his elaborate deep-sea sounding machine, by which, while reliev- 

 ing the delicate sounding wire from the sudden strains to which 

 it would otherwise be exposed by the pitching of the ship while 

 lying to for the purpose of sounding, the profoundest depths are 

 measured with celerity and exactness. 



In this machine the wire passes outboard from, the reeling 

 drum over a guide pulley mounted on a crosshead that works 

 between two upright guide frames. Each of the guide frames 

 incloses a spiral spring called an accumulator, which is connected 

 with the guide pulley by means of a, rope that passes over a pulley 

 at the top of the guide frame. If the ship is suddenly borne upon 

 the top of a wave while the sinker is going down, instead of caus- 

 ing a jerking strain upon the sounding line, the stress is com- 

 municated to the guide pulley, which moves downward under the 

 additional load and extends the accumulator springs ; and, like- 

 wise, when the ship suddenly sinks into the trough of a wave, the 

 tendency to slack the sounding line is counteracted by a rise in 

 the guide pulley brought about by the normal tendency of the 

 accumulator springs to contract. 



A ship regularly engaged in deep-sea sounding usually has the 

 sounding machine mounted at the after end, and when about to 

 sound is brought to a standstill with the stern to the sea. The 

 stray line with the sounding rod and sinker attached is over the 

 guide pulley and carefully lowered to the water's edge, the regis- 

 ter is set to zero, and the deep-sea thermometer is clamped to the 

 sounding line ; a seaman is stationed at the friction line which 

 controls the velocity with which the wire is unreeled, another at 



