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 m 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 shows 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 currents 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 ocean, both by sound and pressure, 
had been made, but in " blue water" every trial was only a failure 
