May 31, 1901.] 
5. The trawl. A large bag-like net, use- 
ful on soft bottoms, over which it will 
pass without digging into the soil. It has 
a larger mouth and greater capacity than 
the dredge. 
6. The tangle-bar, to sweep over rocky 
bottoms on which the other instruments 
would foul and often be lost. It is in effect 
a series of long swabs that will entangle in 
its hempen fibers almost anything from 
coral rock to fishes. It is probably the 
most effective all-around instrument for 
general work, and the least likely to fail or 
be lost. We found it invaluable in West 
Indian waters of moderate depths. 
With these six instruments, then, the 
sea bottom has been sounded, its tempera- 
ture taken, samples of both water and 
bottom secured and specimens of its ani- 
mal life brought to light, both figuratively 
and literally. As yet this vast territory 
has been but seratched here and there. 
We can speak with confidence, however, 
concerning the general physical conditions, 
and we are acquainted with thousands of 
the strange and bizarre creatures that con- 
stitute its fauna. 
Regarding the physical features of this 
under world, the following points are worth 
consideration : 
The temperature is uniformly low, prob- 
ably below 40°, except in enclosed seas in 
tropical regions such as the Red Sea. In 
many places the temperature is actually be- 
low the freezing point of fresh water. I 
well remember the surprise felt by the 
members of a dredging party one exces- 
sively hot day off Havana, indeed within 
sight of the now famous Morro Castle, when 
they plunged their hands in a mass of mud 
brought up in the dredge and found it so 
cold as to make them fairly ache. Of 
course the cold water reaches the surface in 
high latitudes, but it covers the entire floor 
of the ocean at depths over 150 fathoms. 
This practical uniformity of temperature 
SCIENCE. 
843 
over the entire submarine surface of the 
globe plays an important part in the well- 
known wide distribution of deep-sea spe- 
cies. 
The general impression that high tem- 
perature is more favorable than a low one 
for the best development of animal life is 
certainly not true of marine animals in 
general, whatever may be the facts con- 
cerning some special groups. If other con- 
ditions are favorable, a luxuriant fauna will 
be developed in any temperature short of 
the freezing point of salt water. But a 
‘change of temperature, if a sudden one, is 
sometimes the cause of oceanic tragedies of 
frightful extent, a fact illustrated by the 
following example : 
The tile-fish is a deep-water species, liv- 
ing upon the bottom on what is known as 
the Gulf Stream slope, off the New England 
coast. Here the water is normally com- 
paratively warm, coming as it does from 
the superheated region of the Gulf of Mex- 
ico. 
During a series of unusually severe gales 
in the summer of 1882 this mass of water 
was pushed aside, as it were, and replaced 
by the colder water. As a result, mil- 
lions and millions of these fish were killed, 
and their dead bodies literally covered the 
surface of the sea for hundreds of square 
miles. So great was the slaughter that 
for years it was feared that the tile-fish 
were exterminated. Fortunately, however, 
the region has been recolonized, probably 
from the south, and numerous tile-fish have 
been taken during the past two seasons. « 
Probably the most remarkable of the 
conditions of deep-sea life is the enormous 
pressure, which varies of course with the 
depth. At the average depth (2,000 fath- 
oms) the pressure is about two tons to the 
square inch of surface, and at 4,000 fathoms 
each square inch of surface is subject to a 
pressure of about four tons. ‘This fact led 
the earlier physicists to maintain that or- 
