2 THREE CRUISES OF THE '• BLAKE, 



fathoms and " no bottom," or to find, as was found by the 

 " Blake " in the Old Bahama Channel, where the current was 

 runnino' at the rate of four knots an hour, a depth of only four 

 hundred and fifty fathoms when sounding with wire, on the very 

 spot where previous rope soundings indicated eight hundred 

 fathoms and " no bottom." 



This problem of dee23-sea sounding was attacked from many 

 sides by American, English, and French naval officers, and the 

 most successfid results were obtained by increasing the weight 

 of the sinker in proportion to the size of the line. The line was 

 thus gradually diminished in size in order to reduce both its 

 weight and the friction, and comparatively accurate soundings 

 were made with a stout cod-line and a heavy sinker (one hun- 

 dred pounds). This method of sounding had, however, its own 

 objections, for it involved the loss of the line, which was not 

 strong enough to bring back the sinker, and thus also no speci- 

 men of the bottom could be obtained. 



Unsuccessful attempts to sound with wire as a substitute for 

 rope were made as far back as 1849, both by English and Amer- 

 ican naval officers. Their failures led to ever-renewed efforts to 

 improve the methods of sounding with line, and all the recent 

 more accurarte deep-sea soundings taken with rope or line have 

 been made with comparatively small lines weighted with heavy 

 sinkers, which caused the line to run out with great velocity. 

 This velocity, of course, decreased as the depth increased, and 

 the time of reaching the bottom was indicated theoretically by 

 an abrupt change, — one practically, however, very difficult to 

 observe with great accuracy. Consequently, a good deal of line 

 would run out before the certainty of having reached bottom 

 became apparent. 



It is to the need of submarine cables that Thalassography ^ 

 owes its great development. While a knowledge of the depth 

 of the sea is one of tlie first requisites for the laying of cables, 

 the character of the bottom is also an important element, and 

 an instrument which would bring up a good sample of the bot- 

 tom became therefore an absolute necessity. Professor John 



^ The need of some single word to ex- basins has led to the construction of this 

 press the science which treats of oceanic term. 



