1869.] on the Scientific Exploration of the Deep Sea. 



405 



2. An ample supply of Sounding-line was provided, specially manu- 

 factured for the purpose ; this line, made of the best Italian hemp, although 

 no more than 0'8 inch in circumference, bears a strain of 12 cwt. For 

 Soundings within 1000 fathoms' depth, it was found most convenient to 

 employ an ordinary cylindrical Deep-sea Lead weighing 1 cwt., having at its 

 base a conical cup for bringing up mud or sand from the bottom, which 

 is furnished with a circular lid that falls down and closes it in when the lead 

 strikes. — Above the Lead a Water-bottle (§ 19) was attached to the line, by 

 whicha sample of sea-watercould be broughtup from the bottom or from any 

 intermediate depth. And above this again there were attached two or more 

 Thermometers, enclosed in cylindrical copper cases having holes at the top 

 and bottom through which the sea-water streams upwards as the lead de- 

 scends. 



3. The Sounding-lead with its appurtenances is allowed to descend as 

 rapidly as it can carry out the line ; but instead of descending at a con- 

 stantly accelerating rate, it requires more time for every additional 100 

 fathoms ; this retardation being due, not, as is popularly supposed, to an 

 increase in the density of the water*, but to the friction of the sounding- 

 line in its descent, which of course increases with every additional fathom 

 that runs out. It is this friction that produces the chief strain upon the 

 line when the Lead is being drawn up, and renders great caution requisite 

 in regulating the rate of the reeling-in which is effected by the donkey- 

 engine. 



4. For the deeper Soundings, the ' Hydra' Apparatus was employed. 

 The essential principle of this is the same with that of all the other forms 

 of Deep-sea Sounding apparatus now in use ; the weights or sinkers being 

 so attached as to be let go by a mechanical contrivance when it touches the 

 bottom, so that the line is relieved from the duty of raising them to the 

 surface, — the rod or tube alone, with the water-bottle and thermometers, 

 being brought up by it. For Soundings at depths of from 1000 to 

 1500 fathoms, two sinkers, each of 112 lbs., were employed; and for 

 yet deeper soundings three were used. The peculiarity of the 'Hydra' 

 apparatus consists partly in the mechanical contrivance for the detach- 

 ment of the sinkers ; and partly in the construction of the rod which 

 carries them, this being a strong tube furnished with valves that open 

 upwards, so as to allow the water to stream through it freely in its de- 

 scent, whilst they enclose the mud or sand into which the tube is forced 

 on striking the bottom before the sinker is detached f. 



a vessel, however slowly it might be moving through the water, would cause the dredge- 

 line to part, if the strain were sudden instead of gradual. 



* This is so trifling, even at 2\ miles depth, as not to equal the difference in density 

 between fresh and salt water; being estimated by Dr. Miller at certainly not more than 

 1-4 7th cf its volume, whilst sea-water of sp. gr. 1*027 is l-37th heavier than fresh water. 



f A detailed account of this Apparatus will be found in the " Sounding Voyage of 

 II. M.S. 1 Hydra,' " already referred to. 



