METHODS OF OCEANOGRAPHIÇAL RESEARCH 267
are obtained—by means of a pump and rubber hose let down
,
_to the desired depth, or, better, in the water bottle
mentioned above for the collection of water for chemical
examination.
The water is then placed in small glass
"
tubes, which taper to a blunt point at the bottom end, .
and centrifuged for twoor three'minutes.
The surface
water is then poured out of the tubes and the little drop
that remains at the bottom contains the minute plankton
_organisms.
This drop of water is sucked o with aglass
pipette andspread evenly over a glass slide with squares
ruled on it which can then be examined under a microscope
and the organisms present in a given number of squares
counted.
Much interesting work on the geographical distribution
of plankton can also be done on ocean liners.
If small
Silk lters be hung under the salt-water tap in the bathroom
many of the surface—living animals and plants can be
obtained… ï
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of the most important items in the equipment for
oceanographical research is naturally a research ship;
On
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big expeditions a vessel of large size is necessary if the
object is to study the physical and biological conditions
over
extensive arjeas’ and at all depths,
There must be
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plenty of spàceto stow the many
instruments
and
netsÿ
A
winch
capable of holding
several thousand fathoms of strong wire cable has.to_ be
used for working the nets at great depths, andpr'obably
one‘ or two_smaller ones for working small plankton nets,
sounding, and collecting water samples. '
Space Should be
available on board for a working laboratory inwhich the
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Collections can be sorted. and preserved, and*accommodation
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should be provided f0r a
small libraryof the most necessary
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works of reference for the identication of animals and
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