the water to pass freely through the cylinder so that it experiences 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 relieving 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 causing a jerking strain upon the sounding line, the stress is communicated to the guide pulley, which moves downward under the additional load and extends the accumulator springs; and, likewise, 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 register 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