ON DEEP-SEA SOUNDING. 377 



APPENDIX D. 



[Extracts from paper read, and illustrated by apparatus 

 exhibited, before United Service Institution, February 4, 

 1878.] 



THE machine before you is designed for the 

 purpose of obtaining soundings from a ship running 

 at full speed in water of any depth not exceeding 

 100 or 150 fathoms. The difficulties to be over- 

 come are twofold ; first, to get the lead or sinker 

 to the bottom ; and, secondly, to get sure evidence 

 as to the depth to which it has gone down. For 

 practical navigation a third difficulty must also be 

 met, and that is to bring the sinker up again, for, 

 although in deep-sea surveys in water of more than 

 3,000 fathoms depth it is advisable, even when 

 pianoforte wire is used, to leave the thirty or forty 

 pound sinker at the bottom, and bring back only 

 the wire with attached instruments, it would never 

 do in practical navigation to throw away a sinker 

 every time a cast is taken, and the loss of a sinker, 

 whether with or without any portion of the line, 

 ought to be a rare occurrence in many casts. The 

 first and third of these difficulties seem insuperable, 

 at all events, they have not hitherto been over- 

 come, with hemp rope for the sounding line, except 

 for very moderate depths, and for speeds much 



