DEEP-SEA SOUNDING. GSV 



and New York, and in 1888, between Lisbon and the Azores; the> 

 Albatross, in 1886 and 1887, off the American coasts, and in the Caribbean/ 

 Sea and Guli of Mexico; the Essex, in 1886, between the United States 

 and Lisbon ; the Juniata, in 1886, in mid-Atlantic, towards St. Paul's 

 Eock ; and the Dolphin, in 1889, between Lisbon and the United States. 



Having thus enumerated the principal explorations made in the deep 

 sea, we now proceed to give a short description of the apparatus used. 



A special feature in the history of deep-sea sounding machines is the 

 improvement in handiness and compactness resulting from the use of fine 

 steel wire of high tenacity, instead of the hempen rope with its heavy 

 sinkers of 4 to 6 cwt. The apparatus used in ascertaining the depth, 

 and obtaining specimens of the bottom, has also been gradually modified 

 to obviate the difficulties encountered. These chiefly refer to the means 

 of detaching the sounding weights, and to the form of the apparatus 

 which secures a portion of the bottom when it is attained. 



In the Dolphin, 1851 — 1852, the soundings were taken with line 

 •07 inch in diameter, and one or two 32-lb. shot, but it has been ques- 

 tioned, and it certainly seems with reason, whether the evidence upon 

 which the deeper soundings rest is quite valid, as before alluded to. It 

 was considered that an approximation to the true depth obtained could 

 be found by the rate of descent of the line, carefully estimated from 

 numerous experiments, but this, of course, is liable to the vitiating in- 

 fluence of under-currents. In sounding with a line of -07 inch in diameter, 

 the velocity of the descent diminishes, with one 32-lb. shot, from 8-83 feet 

 per second at 50 fathoms, to 2-84 feet at 1,000, and 2-09 feet at 2,000 

 fathoms; and with two 32-lb. shot, from 12-5 feet per second at 50 

 fathoms, to 3*48 feet at 1,000, and 2-99 feet at 2,000 fathoms ; but these 

 figures have been much modified by later experience, as referred to in the 

 description of the wire sounding apparatus. 



Another very important consideration is — ^what effect would under- 

 currents have on the line in passing through it? It is certain that a 

 current must act upon the bight of the sounding-line after the weight has 

 passed through it, and it may operate in swerving the weight itself from 

 its perpendicular descent at great depths. Again, the force exerted by a 

 current against the bight of the sounding-line will have the effect of taking 

 the twine off the reel at nearly double its own velocity. 



From these considerations it was supposed that the depths stated, even 

 when it was certain that the bottom had been reached, were in excess, 

 and this, too, in an uncertain degree. But this source of error was much 

 over-estimated. At that time, there was no experience by which a know- 

 ledge could be acquired as to the movements of the water at any con- 

 siderable depth. But it is now well ascertained, that any movement 

 which would greatly affect the registered depth ceases, as a rule, at a 

 comparatively small depth, and that although the lower strata of ocean 

 waters must have some circulatory movement, this motion is so slow as 

 to be inappreciable by any means hitherto applied to estimate it on the 

 open ocean. In laying a telegraph cable, the strain it exerts is most care- 

 fully and continuously watched by its action on the dynamometer, and 



