30 G PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



of experience show that, as a e^oncral rule, the under currents of 

 the deep sea have force enough to take the line out long after the 

 plummet has ceased to do so. Consequently, there is but little 

 reliance to be placed upon deep-sea soundings of former methods, 

 when the depths reported exceeded eight or ten thousand feet. 



563. Various methods tried or inoposed. — Attempts to fathom the 

 ocean, both b}- sound and pressure, had been made, but out in 

 " blue water " every trial vras only "a failure repeated. The most 

 ingenious and beautiful contrivances for deep-sea soundings were 

 resorted to. By exploding petards, or ringing bells in the deep 

 sea, when the winds were hushed, and all was still, the echo or 

 reverberation from the bottom might, it was held, be heard, and 

 the depth detennined from the rate at which sound travels 

 through water. But, though the concussion took place many 

 feet below the surface, echo was silent, and no answer was re- 

 ceived from the bottom. Ericsson and others constructed deep- 

 sea leads having a column of air in them, which, b}^ compression, 

 would show the aqueous pressure to which they might be sub- 

 jected. This was found to answer well for ordinary purposes, 

 but in the depths of the sea, where the pressure would be equal 

 to several hundred atmospheres, the trial was more than this 

 instrument could stand. Mr. Baur, an ingenious mechanician of 

 New York, constructed, according to a plan which I furnished 

 him, a deep-sea sounding apparatus. To the lead was attached, 

 upon the principle of the screw propeller, a small piece of clock- 

 work for registering the number of revolutions made by the little 

 screw during the descent, and it having been ascertained by 

 experiment in shoal water that the apparatus, in descending, 

 would cause the propeller to make one revolution for every 

 fathom of perpendicular descent, hands provided with the power 

 of self-registration were attached to a dial, and the instrument 

 was complete. It worked beautifully in moderate depths, but 

 failed in blue water, from the difficulty of hauling it up if the 

 line used were small, and from the difficulty of getting it down if 

 the line used were large enough to give the requisite strength for 

 hauling it up. An old sea-captain proposed a torpedo, such as is 

 sometimes used in the whale fishery for blowing up the monsters 

 of the deep, only this one was intended to explode on touching 

 the bottom. It was proposed first to ascertain by actual experi- 

 ment the rate at which the torpedo would sink, and the rate at 

 which the sound or the gas would ascend, and so, by timing the 



