THREE CRUISES OF THE “ BLAKE.” 
н 
І. 
EQUIPMENT OF THE “BLAKE.” 
Tux principal object of the hydrographer is to ascertain the 
depth of the sea at any given point, and this seems at first 
glance a very simple process. Sounding in a few fathoms with 
an ordinary lead-line and a heavy sinker presents no difficulties, 
and even in one hundred fathoms the hand lead-line can be used 
with a moderate degree of accuracy. Beyond this, the problem 
is very different. I well remember my own first experience of 
sounding, in Lake Titicaca, in not more than one hundred and 
fifty-four fathoms, — when more than five hundred fathoms of 
line were payed out and “no bottom” reported. This unsatis- 
factory result was due simply to the insufficiency of weight of 
the sinker. The experience of those who with the ordinary ap- 
paratus have attempted to sound at still greater depths in the 
oceanic basins has been the same. As the sinker descends, the 
weight of the rope to which it is attached becomes, of course, 
greater and greater; the friction also increases to an alarming 
extent ; and the action of the currents, where there are any, on 
the immense surface presented to them by say one thousand or 
fifteen hundred fathoms of two-inch rope, is sufficient not only 
to counteract the very moderate weights used as sinkers, but to 
exert a lateral force so strong in many cases that the depth 
seems to increase in proportion to the amount of line payed out, 
as if it were indeed fathomless. 
It is not astonishing, therefore, to find recorded such extraor- 
dinary depths in some parts of the Atlantic as eight thousand 
