46 
CRUISE OF H.M.S. CHALLENGER. 
mg and resting on the bottom, the “ ketch ” drops 
over a conical end, and thus releases the weights, 
which remain at the bottom. The tube being larger 
than that of the “ Hydra,” it brings up a greater 
quantity of sample from the bottom. 
These rods are only employed when the depths 
are considered to be over 1500 fathoms ; 
for less depths a conical lead weight (Fig. 4) 
is used, which has fitted to its bottom an 
iron cylinder, 3 inches in diameter, with 
butterfly valves at its base for securing 
samples of the ocean bed. 
The line used for sounding is 1 inch in 
circumference, and is specially prepared for 
this service (having a breaking strain of 
14 cwt.) ; it is marked at every 25 fathoms, 
the 25- and 75-fathom marks being white, 
the 50-fathom marks red, and the 100- 
fathom marks blue. Worsted is used to 
mark the line, and the number of hundreds 
are distinguished by tucking the worsted 
under and over the strands of the line, one tuck for 
each hundred fathoms. This leaves the line per- 
fectly smooth ; no additional friction is caused in 
the water, nor is there any danger of the marks of 
the line fouling in the blocks through which it 
passes. The line is kept on reels (3000 fathoms on 
each) conveniently situated near the sounding-plat- 
form, from which it is led through a block to the 
Fig. 4. 
