200 THE PHYSICAL GEOGRAPHY OF THE SEA. 



CHAPTER XL 



THE DEPTHS OF THE OCEAN. 



The Depth of blue Water unknown, ^ 421. — Results of former Methods of Deep-sea 

 Soundings not entitled to Confidence, 422. — Attempts by Sound and Pressure, 423. 

 — The Myths of the Sea, 424. — Common Opinion as to its Depths, 425. — Interest- 

 ing Subject, 427. — The deepest Soundings reported, 428. — Plan adopted in the 

 American Navy, 429. — Soundings to be made from a Boat, 431. — Why the Sound- 

 ing-twine will not stop running out when the Plummet reaches Bottom, 432. — In- 

 dications of under Currents, 433. — Rate of Descent, 434. — Brooke's Deep-sea 

 Sounding Apparatus, 437. — The greatest Depths at which Bottom has been found, 

 438. 



421. Until the commencement of the plan of deep-sea sound- 

 ings, as now conducted in the American Navy, the bottom of what 

 the sailors call " blue water" was as unknown to us as is the inte- 

 rior of any of the planets of our system. Ross and Dupetit Then- 

 ars, with other officers of the English, French, and Dutch navies, 

 had attempted to fathom the deep sea, some with silk threads, 

 some with spun-yarn (coarse hemp threads twisted together), and 

 some with the common lead and line of navigation. All of these 

 attempts were made upon the supposition' that when the lead 

 reached the bottom, either a shock would be felt, or the line, be- 

 coming slack, would cease to run out. 



422. The series of systematic experiments recently made upon 

 this subject s^ows that there is no reliance to be placed on such a 

 supposition, for the shock caused by striking bottom can not be 

 communicated through very great depths, and therefore it does not 

 follow that the line will become slack and cease to run out when 

 the plummet reaches the bottom. Furthermore, the lights of ex- 

 perience show that, as a general rule, the under .jcurrents of the 

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

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

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

 when the depths reported exceeded eight or ten thousand feet. 



423. Attempts to fathom the oces^n, both by sound and pressure, 

 had been made, but in " blue water" every trial was only a failure 



